CN109560450A - Second_harmonic generation - Google Patents
Second_harmonic generation Download PDFInfo
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- CN109560450A CN109560450A CN201811113227.1A CN201811113227A CN109560450A CN 109560450 A CN109560450 A CN 109560450A CN 201811113227 A CN201811113227 A CN 201811113227A CN 109560450 A CN109560450 A CN 109560450A
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- harmonic
- elementary beam
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
- H01S3/106—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity
- H01S3/108—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity using non-linear optical devices, e.g. exhibiting Brillouin or Raman scattering
- H01S3/109—Frequency multiplication, e.g. harmonic generation
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/35—Non-linear optics
- G02F1/37—Non-linear optics for second-harmonic generation
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- Nonlinear Science (AREA)
- Optics & Photonics (AREA)
- Electromagnetism (AREA)
- General Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Plasma & Fusion (AREA)
- Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)
Abstract
A kind of secondary harmonic generator may include combiner, combine elementary beam with remaining elementary beam.Secondary harmonic generator may include the second harmonic crystal for being coupled to combiner, to generate second harmonic light beam from elementary beam and remaining elementary beam.When generating second harmonic light beam, remaining elementary beam may exit off second harmonic crystal.
Description
Technical field
The present invention relates to second_harmonic generations, and more particularly relate to carry out second_harmonic generation using loop structure
Method.
Background technique
Light overtone generation can be used for by laser from wavelength convert be shorter wavelength (i.e. higher frequency).For example, again
Frequency or second_harmonic generation (second harmonic generation:SHG) can be used for obtaining visible light near infrared light.
Frequency doubled light can be subsequently used for generating frequency tripling light, be used for spectroscopy, be used for material processing, for optical pumping (optical
Pumping) and/or the like.
In general, the optical frequency of laser is doubled using nonlinear optical crystal, it is used for using single input light beam with providing
Be converted to a pair of of photon needed for second harmonic.Fig. 1 is showing the schematic diagram of the secondary harmonic generator 10 of the prior art.Such as
Shown in Fig. 1, prior art secondary harmonic generator 10 includes second harmonic crystal 14.At work, the basic light of optical frequency ω
Beam 11 is incident on second harmonic crystal 14.Because the nonlinear conversion efficiency of second harmonic crystal 14 is less than 100%, only
In second harmonic crystal 14 frequency multiplication occurs for a part of elementary beam 11, so that the second harmonic light beam of 2 ω of second harmonic frequency
12 leave second harmonic crystal 14 together with the non-conversion portion 11A of the optical frequency ω of elementary beam 11.Two kinds of light beams leave as a result,
Second harmonic crystal 14: the non-conversion portion 11A and second harmonic light beam 12 of elementary beam 11.In some applications, secondary humorous
Glistening light of waves beam 12 and non-conversion portion 11A can be incident on third overtone crystal (not shown), and a part of these light beams is turned
It is changed to the triple-frequency harmonics light beam of third harmonic frequencies.Alternatively, in some cases, for another purpose, second harmonic light beam
12 can be transmitted.For example, the secondary harmonic generator 10 of the prior art may include dichroscope (or optical filter), again
It guides non-conversion portion 11A and transmits second harmonic light beam 12 as output.
Summary of the invention
According to some feasible embodiments, a kind of secondary harmonic generator may include combiner, by elementary beam
It is combined with remaining elementary beam；With second harmonic crystal, it is coupled to combiner, to generate from elementary beam and remaining elementary beam
Second harmonic light beam, wherein when generating second harmonic light beam, remaining elementary beam leaves second harmonic crystal.
According to some feasible embodiments, method may include: to be propagated elementary beam by secondary harmonic generator
By second harmonic crystal, to generate second harmonic light beam from elementary beam and remaining elementary beam, wherein secondary humorous generating
When glistening light of waves beam, remaining elementary beam may exit off second harmonic crystal；Remaining light substantially is propagated with by secondary harmonic generator
Beam, so that remaining elementary beam enters second harmonic crystal with elementary beam, to generate second harmonic light beam.
According to some feasible embodiments, laser may include: combiner, by elementary beam and remaining light substantially
Shu Zuhe；Second harmonic crystal generates second harmonic light beam from elementary beam and remaining elementary beam, wherein secondary generating
When harmonic optcial beam, remaining elementary beam may exit off second harmonic crystal；With one or more optical components, by remaining light substantially
Beam is directed to combiner.
Detailed description of the invention
Fig. 1 shows the schematic block diagrams of prior art secondary harmonic generator；
Fig. 2A -2D is showing the exemplary of the secondary harmonic generator with the loop structure for second_harmonic generation
The schematic diagram of embodiment；
Fig. 3 is showing the another exemplary of the secondary harmonic generator with the loop structure for second_harmonic generation
The schematic diagram of embodiment
Fig. 4 is the related example of non-colinear phase matched example by the loop structure realization for second_harmonic generation
Property diagrammatic illustration.
Fig. 5 is the flow chart for using the example process of loop structure progress second harmonic optics generation, such as at this
Described in text.
Specific embodiment
Although describing the present invention for various embodiments and example, purpose is not to limit the invention to this reality
Apply example.On the contrary, the present invention covers various changes and equivalents, this is that those skilled in the art should be understood that.
Typical prior art second_harmonic generation scheme (such as shown in the prior art secondary harmonic generator 10 of Fig. 1
) use the conllinear second_harmonic generation of I type.Here, basic photon to be combined is in single incident beam (such as elementary beam
11) the identical photon in.In II type second_harmonic generation, the orthogonal linear polarization of each second harmonic photon
The basic photon of a pair of (linear polarization) state is formed.Input light beam for example can be single circular polarization as a result,
Light beam or single linear polarized beam, relative to two linear conditions to be combined in secondary harmonic generator it is at 45 ° (
The photon of equal amount is provided under either case in each cross-polarization).
In addition to being I type (Type-I) phase matched or II (Type-II) type phase matched, phase matched can be it is crucial or
Non-key.Non-key phase matched (non-critical phasematching) has quick with escaping (walk-off) and angle
The related known advantage of sensitivity.However, non-key phase matched can be difficult to the prior art second_harmonic generation construction (such as
It is shown in FIG. 1) in realize because non-key phase matched depend on and the associated accurate refractive index weight of nonlinear crystalline material
It closes (coincidences of refractive indices), need to usually be assisted by temperature adjustment.Further, existing
Have technology second_harmonic generation construct in, non-colinear phase matched be it is impossible (such as because amount incident photon be same
In elementary beam).Due to these restrictive conditions, for given nonlinear crystal, pass through selection crystal almost without chance
Orientation, polarization orientation (polarization orientation) or phase matched type are non-linear strong to improve and/or optimize
Conversion ratio is spent, or improves and/or optimizes output beam quality by using non-key phase matched, allow bandwidth
(acceptance bandwidth), angular acceptance (angular acceptance) and/or the like.
Prior art secondary harmonic generator further disadvantage is that, it usually needs into the elementary beam of second harmonic crystal
Deep focus to obtain reasonable transfer efficiency.This deep focusing causes the small light spot diameter of elementary beam, this can damage light beam
Quality (such as due to light beam walk-off effect).Further, the deep of elementary beam focuses the table that will cause second harmonic crystal 14
The deterioration (such as after tens of or hundreds of hours exposure) in face.
Some embodiments as described herein are provided loop structure (looped configuration) for secondary humorous
The secondary harmonic generator that wave generates.In some embodiments, loop structure is provided is taken by selection crystal orientation, polarization
Improve and/or optimize the chance of nonlinear strength conversion ratio to, phase matched type and/or the like.Further, ring
Road construction is provided for being improved by using non-key phase matched and/or being optimized output beam quality, allow bandwidth, angular spectrum
The chance (such as compared with prior art secondary harmonic generator) of width and/or the like.Further, for secondary humorous
Wave generate loop structure improve secondary harmonic generator transfer efficiency (such as with prior art secondary harmonic generator ratio
Compared with).
Fig. 2A -2D is showing the example of the secondary harmonic generator 20 with the loop structure for second_harmonic generation
The schematic diagram of property embodiment.
As shown in Figure 2 A, secondary harmonic generator 20 may include second harmonic crystal 24, polarizing filter 25A, polarization
Optical filter 25B, frequency filter 26, reflecting mirror 27 and polarization rotator 28.The component of secondary harmonic generator 20 is described below,
The then exemplary operation of description secondary harmonic generator 20.
Second harmonic crystal 24 includes the component for generating second harmonic light beam.For example, second harmonic crystal can wrap
Crystal is included, crystal includes lithium niobate or another type of nonlinear crystal.It should be noted that in secondary harmonic generator 20, it is secondary
Overtone crystal 24 can execute II type conversion, thus second harmonic crystal 24 in cross-polarization using photon be used for execution to
The conversion of second harmonic.However, in some embodiments, as follows for described in Fig. 3, the second harmonic of loop (looped) is produced
Raw device may include executing the second harmonic crystal of I type conversion (such as thus second harmonic crystal using light in same polarization
Son is for executing the conversion to second harmonic).In some embodiments, second harmonic crystal 24 may include different materials
Material depends on wavelength, power level and/or one or more other parameters.
Polarizing filter 25 (such as polarizing filter 25A, polarizing filter 25B) include for first polarization (such as
Be parallel to the polarization of the page plane of Fig. 2A, be expressed as | | polarization) in basic optical frequency ω transmit (T) light beam and second polarization
With the component of basic optical frequency ω reflection (R) light beam in (such as polarization orthogonal with Fig. 2A page plane, be expressed as ⊥ polarization).By
This is as shown in Figure 2 A, and polarizing filter 25 is properly termed as and/or is expressed as ⊥ R | | T optical filter.By | | base is transmitted in polarization
This light beam and elementary beam is reflected in ⊥ polarization, polarizing filter 25A may be used as polarization combiner (such as by different polarization
In light beam combination combiner).It should be noted that | | polarization and ⊥ polarization are as the cross-polarization with execution II type transfer correlation
Example provides, and other cross-polarizations (such as plane not parallel or perpendicular to Fig. 2) can be used in some embodiments.
Frequency filter 26 includes for basic (1) optical frequency ω reflection (R) light beam and with 2 ω of frequency multiplication (2) optical frequency transmitting
(T) component of light beam.As a result, as shown in Figure 2 A, frequency filter 26 is properly termed as and/or is expressed as 1R2T optical filter.
Reflecting mirror 27 include in any polarization (such as ⊥ polarization in, | | in polarization, and/or the like)
With the component of basic optical frequency ω reflection (R) light beam.As a result, as shown in Figure 2 A, reflecting mirror 27 is properly termed as and/or to be expressed as 1R anti-
Penetrate mirror.
Polarization rotator 28 includes the component (such as being rotated by 90 °) for allowing the polarization of light beam to rotate.For example, polarization rotation
Device 28 can allow elementary beam from | | polarization rotate to ⊥ polarization, and can allow elementary beam from ⊥ polarization rotate to | | polarization,
It is detailed further below.
In the operation of secondary harmonic generator 20, elementary beam 21 (such as with basic optical frequency ω and be in | | polarization)
It is issued towards polarizing filter 25A.As shown, polarizing filter 25A is by elementary beam 21 and remaining elementary beam 21A (example
Such as there is basic optical frequency ω and polarized in ⊥) combination, and elementary beam 21 and remnants elementary beam 21A travel to second harmonic
Crystal 24.Second harmonic crystal 24 may be coupled to polarizing filter 25A and is used for from elementary beam 21 and remaining elementary beam 21A
Second harmonic light beam 22 is generated with 2 ω of frequency multiplication optical frequency.Second harmonic light beam 22 generated in second harmonic crystal 24 (such as using
Elementary beam 21 and remnants elementary beam 21A), and it is directed into the output section of secondary harmonic generator 20.
When generating second harmonic light beam 22, remaining elementary beam 21A (such as with basic optical frequency ω and be in | | polarization
Elementary beam 21 non-conversion portion) may exit off second harmonic crystal 24, and drawn by frequency filter 26 and reflecting mirror 27
Polarization rotator 28 was connected, so that remnants elementary beam 21A rotates to ⊥ polarization.As shown, the remnants through polarization rotation
Elementary beam 21A can be directed to polarizing filter 25A by polarizing filter 25B, for combining with elementary beam 21.
Further, when generating second harmonic light beam 22, remaining elementary beam 21B (such as with basic optical frequency ω and
The non-conversion portion of remaining elementary beam 21A in ⊥ polarization) it may exit off second harmonic crystal 24, and by frequency filter
26 and the guidance of reflecting mirror 27 by polarization rotator 28 so that remnants elementary beam 21B is rotated to | | polarize.As shown, warp
The remaining elementary beam 21B of polarization rotation is conducted through polarizing filter 25B, wherein the remaining elementary beam through polarization rotation
21B can be absorbed by optional beam trap (optical beam dump) (not shown).
Elementary beam 21, remaining elementary beam 21A, remnants elementary beam 21B and second harmonic light beam 22 optical path into one
Step passes through shown in Fig. 2 B-2D.As shown in Figure 2 B, elementary beam 21 (such as with basic optical frequency ω and be in | | polarization) sequence passes
It broadcasts through second harmonic crystal 24, consequently as remaining elementary beam 21A by polarization rotator 28, and is then routed to partially
Polarised filter 25A (such as being polarized with basic optical frequency ω and in ⊥).
As shown in Figure 2 C, remaining elementary beam 21A then propagates through second harmonic crystal 24, consequently as remaining basic
Light beam 21B by polarization rotator 28, and be then routed away from secondary harmonic generator 20 (such as with basic optical frequency ω and
It is in | | polarization), such as reach optional beam trap.
As shown in Figure 2 D, second harmonic light beam 22 is generated in second harmonic crystal 24 (such as using 21 He of elementary beam
Remaining elementary beam 21A), and it is directed into the output section of secondary harmonic generator 20.
The quantity and arrangement of component shown in Fig. 2A -2D provide as an example.In practice, and shown in Fig. 2A -2D
It compares, there may be additional components, less component, different components or the components being arranged differently.For example, although shown in Fig. 2A
Second_harmonic generation scheme use collinear phase matching technology, but in some embodiments, it is one or more additionally and/
Or out of phase matching technique can be implemented in secondary harmonic generator 20, such as key signal phase matching, non-key phase
Match, non-colinear phase matched, quasi-phase matched (such as service life polarization material), and/or the like.In some embodiment party
In formula, due to the loop structure of secondary harmonic generator 20 realize this technology (such as because given photon centering photon (from
It generates second harmonic light beam 22) be from different light beams), as described above.
Further, in some embodiments, one or more types component (such as reflecting mirror, optical filter and/or
It is such) those of (such as in addition to or replace shown in Fig. 2A) can be used, with the light allowed in secondary harmonic generator 20
Beam separation combines, such as dichroic or three-dimensional color thin film filter, polarizing filter, absorbability optical filter, prism, grating
And/or other types optical filter and/or reflecting mirror.Additionally or alternatively, the various sequences of component and/or combination (such as filter
Device, crystal, reflecting mirror and/or the like) it can be used in secondary harmonic generator 20.
In addition, although being not shown in fig. 2 a-2d, in some embodiments, one or more components (such as except
Those of or replace shown in Fig. 2A), such as one or more wave plates, non-planar beam path, lens and/or the like,
It can be included in the appropriate position in secondary harmonic generator 20, in order to provide desired polarization state or expectation beam sizes
And/or profile, this depends on the details of conversion configurations.
In turn, two or more components shown in Fig. 2A -2D can implement in single component or Fig. 2A -2D shown in
Single component may be embodied as multiple distributed elements.Additionally or alternatively, secondary harmonic generator 20 a group parts (such as
One or more components) one or more functions for being described as being executed by another group of secondary harmonic generator 20 can be executed.
Fig. 3 is showing another example of the secondary harmonic generator 30 with the loop structure for second_harmonic generation
The schematic diagram of property embodiment.
As shown in figure 3, secondary harmonic generator 30 may include second harmonic crystal 34 and one group of reflecting mirror 37A to 37D.
The component of secondary harmonic generator 30 is described below, then describes the exemplary operation of secondary harmonic generator 30.
Second harmonic crystal 34 includes for using photon to generate second harmonic in same polarization or in vertical polarization
The component (i.e. the crystal for executing the conversion of I type or the crystal for executing the conversion of II type) of light beam.In some embodiments,
Second harmonic crystal 34 may include lithium niobate or another type of nonlinear crystal.
As shown in figure 3, in some embodiments, second harmonic crystal 34 may include relative to elementary beam 21, residual
Remaining elementary beam 21A, remnants elementary beam 21B and/or the inclined input optical surface 34I of second harmonic light beam 22 and output optics
Face 34O.For example, in some embodiments, inputting optical surface 34I and/or output optical surface 34O can be relative to elementary beam
21, remaining elementary beam 21A, remaining elementary beam 21B, and/or second harmonic light beam 23 are with Brewster angle (Brewster
Angle it) tilts.
Reflecting mirror 37 (such as reflecting mirror 37A, reflecting mirror 37B, reflecting mirror 37C or reflecting mirror 37D) includes for basic
Optical frequency ω reflects the component of (R) light beam (such as in any polarization).As a result, reflecting mirror 37 as shown in Figure 3 be properly termed as and/or
It is identified as 1R reflecting mirror.In some embodiments, reflecting mirror 37 can be regular reflection mirror (not being dichroscope), because
Light beam combination and splitting function pass through the spatial multiplexing (spatial multiplexing) in secondary harmonic generator 30
(such as thus give light beam and be reflected by a reflector and another light beam bypasses reflecting mirror in space) is provided.In some embodiments
In, by allowing remaining elementary beam 21A to turn to towards second harmonic crystal 34, reflecting mirror 37D may be used as angle combiner, so that
Remaining elementary beam 21A combines (such as described below) with elementary beam 21.In some embodiments, reflecting mirror 37D can be with
Including reflecting mirror, as it appears from the above, or another optical element, allow remaining elementary beam 21A and/or elementary beam 21 to turn to, make
It obtains remaining elementary beam 21A and elementary beam 21 is overlapped at second harmonic crystal 34 and (combines).For example, in some embodiment party
Formula, reflecting mirror 37D may include prism, grating, lens, optical fiber, and/or such, be arranged as allowing remaining elementary beam
21A and/or elementary beam 21 turn to.
In operation, the input coupling of elementary beam 21 (such as with basic optical frequency ω) is to second harmonic crystal 34.Such as
Further shown in, second harmonic crystal 34 is coupled to reflecting mirror 37D, so that remaining elementary beam 21A (such as with light substantially
Frequency ω and ω ' is represented as in Fig. 3) second harmonic crystal 34 be in elementary beam 21 combine.Second harmonic crystal 34 from
Elementary beam 21 and remnants elementary beam 21A generates second harmonic light beam 22, and 22 quilt of second harmonic light beam with 2 ω of frequency multiplication optical frequency
The output section of the secondary harmonic generator 30 of guidance.
When generating second harmonic light beam 22, remaining elementary beam 21A (such as non-conversion portion of elementary beam 21) can
To leave second harmonic crystal 34.As shown, remaining elementary beam 21A can be directed back into via reflecting mirror 37A to 37D
The input optical surface 34I of second harmonic crystal 34, for being combined with elementary beam 21.
Further, when generating second harmonic light beam 22, remaining elementary beam 21B (such as remaining elementary beam 21A
Non- conversion portion has basic optical frequency ω and is represented as ω " in Fig. 3) it may exit off second harmonic crystal 34, and be guided
Secondary harmonic generator 30 is left, such as reaches optional beam trap (not shown).
As described above, second harmonic light beam 22 generates in second harmonic crystal 34 (such as uses elementary beam 21 and residual
Remaining elementary beam 21A), and it is guided the output as secondary harmonic generator 30.
As shown in figure 3, in some embodiments, second harmonic crystal 34 can be oriented to so that elementary beam 21 and residual
Remaining elementary beam 21A is illegally to (acute angle) incident angles to the input optical surface 34I of second harmonic crystal 34.In some realities
It applies in mode, elementary beam 21 and remnants elementary beam 21A can form non-zero (acute angle) angle relative to each other.
As a result, in some embodiments, elementary beam 21 and remaining elementary beam 21A can be still with different angle
Enter second harmonic crystal 34 with close enough parallel angle, it is sufficiently long mutual to ensure to have in second harmonic crystal 34
Dynamic length (such as can be from for short-pulse laser less than 1mm to tens of mm's for continuous wave (CW) laser
Length, wherein the length is usually by the practical manufacture length limitation of second harmonic crystal 34).Here, because of 21 He of elementary beam
Remaining elementary beam 21A is non-colinear, so using non-colinear phase matched, in second harmonic crystal 34 in order to provide height
Imitate non-linear conversion.For example, angle and/or these angles between elementary beam 21 and remaining elementary beam 21A with it is secondary humorous
The relationship of the crystal axis of wave crystal 34 may be selected so that and elementary beam 21, remnants elementary beam 21A and secondary humorous
The associated effective refractive index of glistening light of waves beam 22 allows these light beams to propagate with modified phase relation, for efficiently converting.One
In a little embodiments, for obtaining the adjustability of angle between the elementary beam 21 of phase matched and remaining elementary beam 21A
(such as due to using loop structure) be selected phase matching configuration, second harmonic crystal 34 crystal type and/or it is all so
Class provides greater flexibility, to improve and/or transformation efficiency and/or other one or more characteristics.In some realities
It applies in mode, these technologies can be associated with the adjustment of another technology is used, such as crystal temperature effect adjustment, and beam angle is relative to crystalline substance
The adjustment of body axis, and/or the like.
As specific example, in the prior art two using conventional collinear phase matching (such as secondary harmonic generator 10)
In subharmonic generator, due to dispersion, compared with basic optical frequency, the refractive index along particular crystal orientation is under second harmonic optical frequency
It is always different.Prior art secondary harmonic generator can not must use defeated for the two using single polarization as a result,
Polarization mixing between entering and exporting.However, input light beam can be in some second harmonic crystal by non-colinear phase matched
It is angled, allow phase matched in same polarization by input (such as elementary beam 21 and remnants elementary beam 21A)
It is realized with output (such as second harmonic light beam 22) the two.Here, because the nonlinear factor conversion ratio of second harmonic crystal takes
Certainly in relative to each other and relative to crystal axis polarization orientation, so this flexibility can permit stronger nonlinear system
Number is utilized, and thus increases transfer efficiency.As a result, by realizing non-colinear phase matched, with prior art second_harmonic generation
Device compares, and increased transfer efficiency may be implemented in loop secondary harmonic generator.
As another concrete example utilized for the non-colinear phase matched that second_harmonic generation is realized by loop structure
Son, non-colinear phase matched may be implemented to realize in some second harmonic crystal non-key phase matched (such as in output and
Its polarization is aligned with crystal axis, and when phase matched is to crystal tilting sensitivity unwise there are single order).In some embodiments
In, this non-key phase matched construction for example reduces light beam escaping amount by providing the relatively high angle of divergence for input light beam
And/or the angular-sensitive measurement of reduction.
Fig. 4 is the non-colinear phase realized by the loop structure (such as shown in Fig. 3) for second_harmonic generation
40 are shown with the related example illustration of example.Fig. 4 is showing the second harmonic crystal formed for the lithium niobate of magnesium doping
34, from 0 DEG C to about 180 DEG C within the temperature range of the ordinary index of refraction at 1064 nanometers (nm) (such as IR wavelength)
Extraordinary refractive index when (ordinary refractive index) and 532nm (such as green wavelength)
The figure of (extraordinary refractive index).
As shown in figure 4, these refractive index it is equal and therefore phase matched when temperature be about 110 DEG C of (T0=110 DEG C).?
In the example, this phase-matching temperatures can be reduced by using non-colinear phase matched.For example, due to using loop structure
It makes, a pair of of light beam (such as elementary beam 21 and remnants elementary beam 21A) of IR wavelength can be directed so that these light beams
Second harmonic crystalline substance is incident in the ordinary plane with opening half angle (opening half-angle) φ with a variety of directions
Body.It is ordinary n with the associated refractive index of IR light beamo1And with second harmonic light beam (such as the second harmonic that is generated under green wavelength
Light beam 22) associated refractive index is pure extraordinary ne2.Here, allow green light wave vector equal with two IR wave vectors and thus
ne2=no1Cos φ indicates phase matched.For being lower than T0Temperature, can will be with IR by the non co-linearity that loop structure is realized
The associated ordinary index of refraction of wavelength is reduced to and the associated extraordinary refractive index of green wavelength.For example, between these refractive index
Approximation relation can be indicated by following formula:
ne2=no1[1-3×10-5(T0-T)]
The formula is equal to non-colinear ne2=no1cosφ≈no1(1-φ2/ 2) following formula, is obtained:
φ2=6 × 10-5(T0-T)
Therefore, in order to for example about 30 ° (T=30 °) at a temperature of operate, above formula estimation can produce φ=
0.07radians, this corresponds to 4 ° of half angle or 8 ° of full angle between two IR light beams.By this method, non-colinear phase
Position matching can make non-key phase matched more easily realize, be thus taken into account and implement in loop second_harmonic generation scheme
Extra phase matching configuration (such as compared with prior art secondary harmonic generator).
As described above, Fig. 4 is only provided as an example.Other examples are also possible, and can with for described in Fig. 4
It is different.
Fig. 3 is returned, in some embodiments, elementary beam 21 can polarize (such as | | polarize) in the plane of Fig. 3,
In the plane polarization (such as in ⊥) perpendicular to Fig. 3, polarized with another angle (such as 45° angle degree) of the plane relative to Fig. 3,
And/or the like.As a result, in some embodiments, second harmonic crystal 34 may be selected so that second harmonic crystalline substance
Body 34 executes the conversion of I type or the conversion of II type.In the case where second harmonic crystal 34 executes the conversion of II type, secondary harmonic generator
It may include polarization rotator (not shown), remaining elementary beam 21A allowed (such as to rotate relative to the rotation of elementary beam 21
90°)。
Further, as shown in figure 3, in some embodiments, the loop structure of secondary harmonic generator 30 can not
Need wave plate, dichroic mirror, and/or it is such by remaining elementary beam 21A and/or remnants elementary beam 21B from
Second harmonic light beam 22 separates.(such as reflecting mirror 37A is arrived on the contrary, these light beams can separate in space as shown in Figure 3
Remaining elementary beam 21A is only coupled to second harmonic crystal 34 by 37D).In some embodiments, in elementary beam 21 and residual
Remaining elementary beam 21A is when having different incidence angles on the input optical surface 34I of second harmonic crystal 34, elementary beam 21 and residual
Remaining elementary beam 21A can be substantially non-colinear in second harmonic crystal 34.
The quantity and arrangement of component shown in Fig. 3 provide as an example.In practice, compared with shown in Fig. 3, Ke Yicun
In additional components, less component, different components or the component being arranged differently.For example, although second harmonic shown in Fig. 3 produces
Raw scheme uses the non-colinear phase-matching technique with the conversion of I type, in some embodiments, it is one or more additionally and/
Or out of phase matching technique (such as with the conversion of I type or the conversion of II type) can be implemented, example in secondary harmonic generator 30
Such as key signal phase matching, non-key phase matched, collinear phase matching, quasi-phase matched, and/or such.In some realities
Apply in mode, due to secondary harmonic generator 30 loop structure and realize this technology, as described above.Further, component
Various sequences and/or combination (such as optical filter, crystal, reflecting mirror and/or the like) second_harmonic generation can be used in
In device 20.
In addition, although being not shown in Fig. 3, in some embodiments, one or more components (such as in addition to or
Instead of it is shown in Fig. 3 those), such as one or more wave plate, non-planar beam path, lens and/or the like can be by
Including the appropriate position in secondary harmonic generator 30, in order to provide desired polarization state or expectation beam sizes and/or
Profile, this depends on the details of conversion configurations.
In turn, two or more components shown in Fig. 3 can be implemented or single component shown in Fig. 3 in single component
It may be embodied as multiple distributed elements.Additionally or alternatively, a group parts of secondary harmonic generator 30 (such as one or more
A component) one or more functions for being described as being executed by another group of secondary harmonic generator 30 can be executed.
In some embodiments, loop structure as described above can provide the production of the prior art second harmonic than Fig. 1
The raw higher transfer efficiency of device 10.For example, conversion efficiency of second harmonic depends on the input power density of basic optical frequency ω.Existing
There is technology secondary harmonic generator 10, the general power input of second harmonic crystal 14 is limited to produce prior art second harmonic
The general power of raw device 10 inputs P.It (such as is secondary harmonic generator 20 and second harmonic respectively to second harmonic crystal 24/34
Generator 30) total optical power input be substantially larger than P because at least some power can be used twice at ω (such as due to
Loop structure, wherein remnants elementary beam 21A is used together with elementary beam 21, for generating second harmonic light beam 22).As a result
It is, at loop secondary harmonic generator (such as secondary harmonic generator 20, secondary harmonic generator 30, and/or such)
In power density and transfer efficiency than higher in prior art secondary harmonic generator 10.
Further, in loop secondary harmonic generator, remaining elementary beam 21B is prevented from being again introduced into second harmonic
Crystal 24/34, to avoid potential optical interference effects.In other words, the optical path of elementary beam 21 and remaining elementary beam 21A
It can be not form closed loop under various optical frequencies or do not form optical cavity (optical under independent light with optical arrangement
cavity).Closed loop or optical cavity is avoided to can contribute to the stability of second_harmonic generation process under each optical frequency.
In some embodiments, second harmonic crystal 24/34 can use Brewster angle and enter and/or leave.?
In some embodiments, Brewster angle enter and/or leave can reduce second harmonic crystal 24/34 (such as confrontation
Reflect (AR) coating replacement, have impaired tendency) on surface loss.In some embodiments, Brewster
Surface is only low-loss for specific polarization (such as p-polarization, can correspond to as described above | | polarization).By
This, in angular multiplexed (angle-multiplexed) second_harmonic generation scheme (such as shown in Fig. 3), wherein elementary beam 21,
Remaining elementary beam 21A and second harmonic light beam 22 are in p-polarization, entered using Brewster angle and/or when leaving these
Light beam can have low surface loss, this helps to obtain high conversion efficiency.Although should be noted that these light beams relative to secondary humorous
Wave crystal 34 can have different incidence angles, and surface loss amount is usually at the several years of best Brewster angle (such as 5 ° or smaller)
In the range of be acceptable.Entered using Brewster angle and/or another advantage for leaving is, in output section (such as defeated
Optical surface 34O out) refraction can be used for second harmonic light beam 22 from remaining elementary beam 21A and remaining elementary beam 21B
It separates (such as shown in Fig. 3).
In some embodiments, Brewster angle enters and/or leaves that be also used in not all light beam inclined all in p
In the system of vibration.For example, one outputs and inputs and can thus exist through p-polarization in II type conversion plan (such as shown in Fig. 2A)
There is low surface loss on second harmonic crystal.Other inputs can polarize that (such as it can correspond to ⊥ as described above through s
Polarization), and corresponding loss can receive, or can be applied to second harmonic crystal for the AR coating of s polarization optimization.Some
In embodiment, if the input polarized through s can be remaining elementary beam using the brewster surface without coating
21A (such as not being elementary beam 21), to make only (such as input face in second harmonic crystal) because in second harmonic
The loss of remaining elementary beam 21A at the output face of crystal does not influence transfer efficiency and causes the generation of surface loss.
Loop secondary harmonic generator (such as secondary harmonic generator 20, secondary harmonic generator 30 and/or it is all so
Class) another feature be because elementary beam 21 and remnants elementary beam 21A are emitted to respectively in second harmonic crystal 24,
So can by adjusting loop secondary harmonic generator another component (such as polarizing filter 25A, polarizing filter 25B, instead
Mirror 37C, reflecting mirror 37D are penetrated, and/or the like) and optimize elementary beam 21 for specific transformed structure and remnants are basic
The position of light beam 21A and angle.As a result, for example, being compensated for escaping, it may not be necessary to which birefringent or dispersion goes away plate (walk-
off plate).Similarly, for non-colinear phase matched, it may not be necessary to which prism or other dispersive components form light substantially
Expected angle between beam 21 and remaining elementary beam 21A.
Further, because light is advanced the required time around loop secondary harmonic generator, remaining elementary beam 21A is opposite
Reach second harmonic crystal 24/34 in the delay of elementary beam 21.As a result, in general, the construction is adapted to have input pulse
Operation, Duration Ratio light time needed for loop traveling are longer.The size of this loop for example can be one centimetre
Or bigger (such as 3 centimetres (cm)), the corresponding pulse duration with about 100 picoseconds.Loop as described above is secondary humorous as a result,
Wave switch technology can be well adapted for generating the Optical Maser System of nanosecond or more long pulse, for example, Q-switch solid laser and
CW laser.Can be used millimeter or smaller size of micro-optical device construction compared with minor loop addressing picosecond pulse (such as from
Mode-locked laser (mode-locked lasers).
Loop structure can be used for a variety of pulses, if loop two-way time is selected as being approximately equal to interpulse period
Or the multiple of interpulse period, then each pulse length for having of a variety of pulses is more shorter than loop two-way time.?
Under latter case, the input to second harmonic crystal 24/34 includes new pulse and the pulse generated from pulse earlier.For example,
When CW mode-locked laser can be continuously conveyed about 10 picoseconds or shorter lasting with the repetitive rate of tens of MHz to tens of GHz ranges
Between pulse.For 200MHz mode-locked laser, for example, having for (to correspond to the total optical path length of 150cm 5 loop two-way times nanosecond
Degree) loop secondary harmonic generator allow using the light from previous pulse and by each pulse doubling.The construction provide with
The advantages of single longer pulse situation identical improvement transfer efficiency.Even for the pulse burst (pulse for only including two pulses
Burst), and there are advantage, because two input pulses are effectively combined as a second harmonic pulse, can be directed to
Given peak input power generates bigger output peak power.
In some embodiments, loop secondary harmonic generator (such as secondary harmonic generator 20, second_harmonic generation
Device 30, and/or the like) delay time (herein referred as harmonic generator delay time) can be designed as being approximately equal to laser
The two-way time (herein referred as laser source two-way time) in source or its approximate integral multiple.For example, loop secondary harmonic generator
Delay time can be designed so that delay time be approximately equal to provide elementary beam 21 laser source laser source two-way time
Or its integral multiple.
The delay time of harmonic generator can be limited to the time quantum that light beam is advanced through harmonic generator.Delay time
Also it is considered the optical path length that light beam is advanced in harmonic generator.The optical path length and loop second harmonic advanced
The refractive index for the material that the physical separation and light beam of the component of generator are passed through is related.Two-way time is starting point and end
Point is the more specific situation of the delay time of same point.
As an example using Fig. 2A, light beam can be limited to the time by the two-way time of secondary harmonic generator 20
Amount is from the time of the process of elementary beam 21 polarizing filter 25A to the remaining elementary beam 21A come from elementary beam 21
Reach the time of same polarizing filter 25A.In optical path remaining elementary beam 21A (or 21B) overlapping elementary beam 21 (or
21A) other points being overlapped can be used for limiting the two-way time of light beam in secondary harmonic generator 20.
Use Fig. 3 as another example, light beam can be limited to for the moment by the two-way time of secondary harmonic generator 30
The area of a room, the time quantum are time for being incident on the input optical surface 34I of second harmonic crystal 34 from elementary beam 21 to from base
The time of this light beam 21 and the input optical surface 34I of next remaining elementary beam 21A arrival second harmonic crystal 34.In optical path
Remaining elementary beam 21A (or 21B), which is overlapped other points that elementary beam 21 (or 21A) is overlapped, can be used for limiting second harmonic production
The two-way time of light beam in raw device 30.
Laser source two-way time can be defined as light beam and pass fully through the chamber of laser source to terminate edge and to start phase
The time quantum of equidirectional traveling.For example, in linear cavity, laser source two-way time is light beam from the specified point row in cavity
Into, from the reflection of chamber terminal reflector (cavity end mirror), reflected from another chamber terminal reflector and proceed back to chamber
In same specified point time quantum, in this process also twice pass through one or more laser gain mediums.In typical situation
Under, the fluctuation of laser source is substantially repeated when laser source is associated continuous round-trip.
In some embodiments, the laser source of elementary beam 21 can be with more longitudinal mode (multi-longitudinal
Mode it) operates.In this case, the power of laser source is fluctuated due to mode beating (mode beating).Typically for solid
State laser source, with a picosecond scale fluctuation, and with a picosecond scale, power output can be flat from changing to close to more than zero time for this fluctuation
Equal power output.Because laser source two-way time can be several nanoseconds, in the given round-trip period of laser source, there are thousands of
Fluctuation can introduce noise into the light beam exported by laser source.
Typical standard nonlinear second-harmonic conversion scheme (such as the prior art secondary harmonic generator for Fig. 1
It is described) these fluctuations can be had benefited from, especially under low conversion restrictive condition.For example, the high power of elementary beam 11 fluctuates
Second harmonic light beam 12 is converted to strongly.The nonlinear characteristic of this coupling implies, and converts with mean power by relatively low function
The fluctuation reduction of rate is compared, and mean power conversion increases more by high-power fluctuation.
In loop secondary harmonic generator, second harmonic crystal 24/34 is based on elementary beam 21 and remaining elementary beam
The combination of 21A generates second harmonic light beam 22.Here, because remnants elementary beam 21A enter second harmonic crystal 24/34 it
It is preceding from 21 traveling different light paths of elementary beam, so the fluctuation in fluctuation and remaining elementary beam 21A in elementary beam 21 exists
When into second harmonic crystal 24/34 can asynchronous (can temporarily be misaligned), this prevents power conversion because fluctuation enhances.It changes
Sentence is talked about, and second harmonic crystal 24/34 directly receives elementary beam 21 from laser source, and receives remaining base via the optical path of loop
This light beam 21A.Thus, it can be different with remaining elementary beam 21A by the received elementary beam 21 of secondary harmonic generator 24/34
Step, this can reduce the generation of second harmonic light beam 22.
However, as described above, the fluctuation of laser source is shown greatly associated continuous round-trip with laser source and is repeated.Here, to the greatest extent
Pipe there may be the gradually changing of perturbation waveform (such as with it is tens of to it is hundreds of this back and forth for time scale), but from a laser
Source round-trip (such as round-trip for the first time) to the time it is upper it is neighbouring it is round-trip (such as second it is round-trip, third time is round-trip or the 4th time past
Return) perturbation waveform change it is smaller, this make waveform almost have periodically.It can be seen that can be by by loop two
Subharmonic generator (such as THG) delay time be designed as being approximately equal to laser source two-way time (such as Tsource) or its approximation
Integral multiple and obtain power conversion enhancing.Here, although elementary beam 21 and remnants elementary beam 21A are entering second harmonic crystalline substance
It will not be correctly aligned when body 24/34, but due to the nearly periodicity of perturbation waveform, fluctuation can be with near-synchronous.
It in some embodiments, can be based on the layout designs loop second_harmonic generation of loop secondary harmonic generator
The delay time of device.For example, loop secondary harmonic generator one or more components (such as second harmonic crystal 24/34, partially
Polarised filter 25A, polarizing filter 25B, frequency filter 26, reflecting mirror 27/37, polarization rotator 28 and/or it is all so
Class) may be arranged such that the nonlinear optical loop because of the part relation with loop secondary harmonic generator caused by when postponing
Between be approximately equal to laser source two-way time or the approximate integral multiple equal to laser source two-way time.Property as a specific example, loop two
One or more components of subharmonic generator can position (such as gluing, soldering, bolt) be so that, one or more components
The distance between make the round-trip optical path length of nonlinear optical loop length matching laser source (be approximately equal therewith or it is close
Like integral multiple) so that the delay time of loop secondary harmonic generator is approximately equal to laser source two-way time or makes its approximation
Integral multiple.In other words, loop two can be designed based on the positioning of one or more components of loop secondary harmonic generator
The delay time of subharmonic generator.
In some embodiments, linear building process can be used in the delay time design of loop secondary harmonic generator
(linear build process) is implemented.Linear building process may include in the component for placing loop secondary harmonic generator
Laser source (such as in the packaging part for installing laser source and loop secondary harmonic generator) is manufactured before.For example, laser source
The mode beating period can be locked (such as in entire service life of laser source) after laser source manufacture, and another laser source
The mode beating period (such as in the manufacture of another moment) can be with the difference of the laser source.In other words, different laser sources
The mode beating period can be slightly different.In this way, a laser source, for another, the round-trip optical path length of laser source can
With difference.
Here, once having manufactured laser source, then linear building process may further include the round-trip light of determining laser source
Road length, determines non-linear optical path length, and non-linear optical path length is matched with the round-trip optical path length of laser source (such as to be considered
When the diffraction efficiency of the component materials of loop secondary harmonic generator), and place and/or manufacture loop secondary harmonic generator
Component, so that the round-trip optical path length of the non-linear optical path length of loop secondary harmonic generator and laser source, so that ring
The delay time of road secondary harmonic generator is approximately equal to the approximate integral multiple of laser source two-way time or laser source two-way time.
In this case, the component of loop secondary harmonic generator be secured in position (such as component can it is in place with gluing, soldering is in place,
Bolt is in place, etc.) make the non-linear optical path of loop secondary harmonic generator and delay time is to cannot be adjusted (i.e. fixed).
Additionally or alternatively, adjustable mechanical part can be used in the delay time design of loop secondary harmonic generator
Implement, such as micrometer, turntable or adjustable mirror unit, allows one or more optical components in non-linear optical path
Movement, such as reflecting mirror or prism, thus allow the delay time of non-linear optical path to be adjusted.It can be with comprising adjustable integeral part
It is able to after allowing non-linear optical path length to be assembled in the packaging part for installing laser source and loop secondary harmonic generator
Change.In this case, laser source and loop secondary harmonic generator can be in the round-trip optical path lengths that laser source has been determined
It assembles before in an enclosure.It here, after assembling, can be true accordingly, it may be determined that the round-trip optical path length of laser source
Fixed and laser source the matched non-linear optical path length of round-trip optical path length, and it is secondary that adjustable integeral part adjustment loop can be used
The non-linear optical path of harmonic generator.
Fig. 5 is the flow chart for using the example process 50 of loop structure progress second harmonic optics generation, is such as existed
It is as described herein.In some embodiments, example process 50 can be (such as secondary humorous by loop secondary harmonic generator
Baud generator 20, secondary harmonic generator 30 and/or the like) it executes.
As shown in figure 5, process 50 may include propagating elementary beam by second harmonic crystal, with from elementary beam and residual
Remaining elementary beam generates second harmonic light beam (segment 51).For example, as above being produced for secondary harmonic generator 20 and second harmonic
Described in raw device 30, the loop secondary harmonic generator can propagate elementary beam by second harmonic crystal, with from basic
Light beam and remaining elementary beam generate second harmonic light beam.
In some embodiments, when generating second harmonic light beam, remaining elementary beam may exit off second harmonic crystalline substance
Body, as above for described in secondary harmonic generator 20 and secondary harmonic generator 30.
Further as shown in figure 5, process 50 may include propagating remaining elementary beam, so that remaining elementary beam is with basic
Light beam enters second harmonic crystal, to generate second harmonic light beam (segment 52).For example, loop secondary harmonic generator can be with
Remaining elementary beam is propagated, so that remaining elementary beam enters second harmonic crystal with elementary beam, to generate second harmonic
Light beam, as above for described in secondary harmonic generator 20 and secondary harmonic generator 30.
Although Fig. 5 shows the exemplary segment of process 50, in some embodiments, with segment shown in fig. 5
It compares, process 50 may include the segment of additional segment, less segment, different segments or different arrangements.In addition it or replaces
Ground is changed, two or more segments in process 50 can execute parallel.
Some embodiments as described herein are provided loop structure (looped configuration) for secondary humorous
The secondary harmonic generator that wave generates.In some embodiments, loop structure is provided is taken by selection crystal orientation, polarization
Improve and/or optimize the chance of nonlinear strength conversion ratio to, phase matched type and/or the like.Further, ring
Road construction provide for by using be easier realize non-key phase matched improve and/or optimization output beam quality,
Allow the chance (such as compared with prior art secondary harmonic generator) of bandwidth, angular acceptance and/or the like.Further
Ground, the transfer efficiency that the loop structure for second_harmonic generation improves secondary harmonic generator are (such as secondary with the prior art
Harmonic generator compares).
Foregoing description provides showing and describsion, but purpose is not meant to embodiment is exhaustive or is limited to disclosed
Exact form.It can make a change and modify in light of the foregoing or from the implementation process of specific embodiment.
Even if the specific combination of feature is recorded in claim and/or discloses in the description, the purpose of these combinations
Nor the possible embodiment that limitation is of the invention.In fact, these many features can be recorded with not specific in claim
And/or not specifically disclosed various modes combine in specification.Although each dependent claims can directly be subordinated to one
A claim, but the disclosure of embodiments possible includes each of with other claim combinations each in claims
Dependent claims.
Element used herein, movement or instruction shall not be construed as be it is crucial or essential, unless otherwise retouching
It states.In addition, as used herein, the purpose of the article " one " be include one or more project, and can be replaced with " one or more "
Change use.In turn, as used herein, term " group " should be include one or more projects (such as associated item, dereferenced item
Mesh, associated item and the combination of dereferenced project etc.), and can be replaced with " one or more ".Referring to only one project
In the case where, use term "one" or similar term.In addition, as used herein, term " having ", "include", "comprise"
Etc. the term that should be opening.Further, phrase " being based on " should be " being based at least partially on ", unless otherwise indicated.
Claims (20)
1. a kind of secondary harmonic generator, comprising:
Combiner combines elementary beam with remaining elementary beam；With
Second harmonic crystal, is coupled to combiner, to generate second harmonic light beam from elementary beam and remaining elementary beam,
Wherein, when generating second harmonic light beam, remaining elementary beam leaves second harmonic crystal.
2. secondary harmonic generator as described in claim 1, wherein elementary beam is in the first polarization and remaining elementary beam
It is polarized in second,
Wherein the second polarization and the first polarized orthogonal, and
Wherein second harmonic crystal executes II type phase matched.
3. secondary harmonic generator as described in claim 1, wherein elementary beam is in the first polarization and remaining elementary beam
It is polarized in second,
Wherein the second polarization and the first polarized orthogonal, and
Wherein combiner is polarization combiner, by elementary beam and remaining elementary beam combination.
4. secondary harmonic generator as described in claim 1, wherein elementary beam is incident on second harmonic crystalline substance with first angle
On the input optical surface of body, and remaining elementary beam is incident on the input optical surface of second harmonic crystal with second angle,
Wherein first angle is different from second angle, and
Wherein second harmonic crystal executes non-colinear phase matched.
5. secondary harmonic generator as claimed in claim 4, wherein second harmonic crystal executes I type phase matched or II type phase
Position matching.
6. secondary harmonic generator as claimed in claim 4, wherein second harmonic crystal executes non-key phase matched.
7. secondary harmonic generator as described in claim 1, wherein elementary beam is incident on second harmonic crystalline substance with first angle
On the input optical surface of body, and remaining elementary beam is incident on the input optical surface of second harmonic crystal with second angle,
Wherein first angle is different from second angle, and
Wherein combiner is angle combiner, at least to allow remaining elementary beam to turn to, so that remaining elementary beam is with second angle
It is incident on the input optical surface of second harmonic crystal.
8. secondary harmonic generator as described in claim 1, wherein elementary beam, remaining elementary beam or second harmonic light
Beam enters with about Brewster angle or leaves second harmonic crystal.
9. secondary harmonic generator as described in claim 1, wherein with secondary harmonic generator associated circuit two-way time
It is approximately equal to the multiple of the either interpulse period of elementary beam laser source interpulse period of elementary beam laser source.
It is wherein more shorter than circuit two-way time with the associated pulse length of laser source.
10. secondary harmonic generator as described in claim 1, wherein with secondary harmonic generator associated circuit two-way time
It is approximately equal to times of the either laser source two-way time of elementary beam laser source laser source two-way time of elementary beam laser source
Number.
Wherein laser source is with more longitudinal modal operations, and
Wherein laser source is continuous-wave laser, or longer than circuit two-way time with the associated pulse length of laser source.
11. a kind of method, comprising:
Elementary beam is propagated through second harmonic crystal by secondary harmonic generator, with from elementary beam and remaining light substantially
Beam generates second harmonic light beam,
Wherein, when generating second harmonic light beam, remaining elementary beam leaves second harmonic crystal；With
Remaining elementary beam is propagated by secondary harmonic generator, so that remaining elementary beam enters second harmonic with elementary beam
Crystal, to generate second harmonic light beam.
12. method as claimed in claim 11, wherein elementary beam is in the first polarization and remaining elementary beam is in second
Polarization,
Wherein the second polarization and the first polarized orthogonal.
13. method as claimed in claim 12 further comprises that remaining elementary beam is allowed to rotate to second partially from the first polarization
Vibration.
14. method as claimed in claim 11, wherein elementary beam is incident on second harmonic crystal with first angle, and residual
Remaining elementary beam is incident on second harmonic crystal with second angle,
Wherein first angle is different from second angle.
15. method as claimed in claim 11, wherein second harmonic crystal executes I type phase matched or II type phase matched.
16. method as claimed in claim 11, wherein second harmonic crystal executes non-key phase matched.
17. method as claimed in claim 11, wherein elementary beam, remaining elementary beam or second harmonic light beam are with about
Brewster angle enters or leaves second harmonic crystal.
18. method as claimed in claim 11, wherein the surface of second harmonic crystal is coated with anti-reflection coating.
19. a kind of laser, comprising:
Combiner combines elementary beam with remaining elementary beam；
Second harmonic crystal generates second harmonic light beam from elementary beam and remaining elementary beam,
Wherein, when generating second harmonic light beam, remaining elementary beam leaves second harmonic crystal；With
Remaining elementary beam is directed to combiner by one or more optical components.
20. laser as claimed in claim 19, wherein second harmonic crystal will execute at least one of the following:
I type phase matched；
II type phase matched；
Non-colinear phase matched；Or
Non-key phase matched.
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| US15/716,159 | 2017-09-26 | ||
| US15/716,159 US10228607B2 (en) | 2014-05-22 | 2017-09-26 | Second harmonic generation |
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