JP2981671B2 - Laser diode pumped solid state laser - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a laser diode-pumped solid-state laser in which a solid-state laser rod is pumped by a semiconductor laser (laser diode), and more particularly, to the solid-state laser rod itself. The present invention relates to a laser-diode-pumped solid-state laser that has a wavelength conversion function and converts the wavelength of a fixed laser oscillation beam and another laser beam into a sum frequency.

(Prior Art) As described in, for example, SPIE Vol. 1104 p100 March 1989, a solid-state laser rod doped with a rare earth such as Nd (neodymium) and having a light wavelength conversion function is formed of Nd: COANP, Nd: PNP and the like are known. As such solid-state laser rod, as described in the magazine _{p132, Nd: Li Nb O 3} , NYAB (Nd x Y 1-x Al 3 (BO
_{3) 4} x = _0.04~0.08), etc. are also known, which are, Self
-Frequency-Doubling Crystal.

As laser diode pumped solid-state lasers using these, SPIE Vol. 1104 p132 March 1989,
As shown in Laser Research Vol. 17 No. 12 p48 (1989), it is known to use a NYAB crystal and obtain the second harmonic of the oscillated laser beam by laser diode pumping. Also, J.Opt.Soc.Am Vol.3 p140 (1986)
Discloses that Nd: Mg O: Li Nb O ₃ is excited by a dye laser having a wavelength of 0.60 μm to obtain a second harmonic of an oscillation laser beam.

Furthermore, for example, in SPIE Vol.1104 p13 March (1989), an Nd-doped YAG laser solid rod and a KTP single crystal that converts the wavelength of the solid laser oscillation beam are arranged in its resonator, and the solid laser oscillation beam It is shown that a sum frequency of the light and the pumping light is obtained.

(Problems to be Solved by the Invention) However, in a conventional solid-state laser having such a wavelength conversion function, a nonlinear optical crystal, a solid-state laser rod, an output mirror, and an oscillating laser beam are longitudinally singulated into a single wavelength-converted wave. An optical element such as an etalon plate or a wavelength plate having a function of stabilizing the power of the laser is fixedly arranged and separately processed, polished, and coated as a laser component. For this reason, scattering of the oscillating laser beam and absorption, scattering, reflection, etc. by the respective coating films occur on the processing surface, and furthermore, the internal loss in the resonator is very large, several% or more due to the absorption inside each component. Had become something. These internal losses increase as the number of parts increases. Therefore, there is a problem that the oscillation laser power in the resonator is reduced, and as a result, the wavelength conversion efficiency is reduced.

In addition, since the above-mentioned internal loss is conventionally as high as several percent, a high-output array laser is generally used as a pump light source of a solid-state laser. That is, the loss in the resonator is thereby covered, and a high output internal power of the resonator is obtained, thereby improving the wavelength conversion efficiency. However, in the conventional array laser, the oscillation efficiency of the solid-state laser is low because its spectral line width is several nanometers, and this has led to a decrease in energy use efficiency.

In particular, the etalon plate and wave plate inserted into the resonator to stabilize the power of the wavelength-converted wave must use a high-output array laser or broad-area laser to greatly increase the internal loss. I didn't get it. Also, if these wavelength plates and etalon plates are removed to eliminate the insertion loss, if the second harmonic of the oscillating laser beam is obtained, the mode between the longitudinal modes of the oscillating laser beam by the nonlinear optical element will be required. There was a problem that power became unstable due to competition.

The present invention has been made in view of the above circumstances, and has as its object to provide a laser diode-pumped solid-state laser having high wavelength conversion efficiency, high energy use efficiency, and stable wavelength-switched wave power. It is assumed that.

(Means and Actions for Solving the Problems) The first laser diode-pumped solid-state laser of the present invention comprises a solid-state laser rod doped with a rare-earth element such as Nd and having an optical wavelength conversion function as described above. In the solid-state laser pumped by a laser diode, both ends of the solid-state laser rod are used as resonator mirrors, and the sum frequency of the oscillating laser beam and the semiconductor laser beam is extracted.

Further, the second laser diode-pumped solid-state laser of the present invention is a laser diode-pumped solid-state laser in which a solid-state laser rod doped with a rare earth such as Nd and having a light wavelength conversion function is pumped by a semiconductor laser as described above. An optical element such as an etalon or a wavelength plate having a function of stabilizing the power of the wavelength-converted wave is attached to one end surface of the solid-state laser rod and integrated, and one side of the optical element is connected to a resonator mirror of the solid-state laser. On the other hand, a resonator is constituted by using the other end face of the solid-state laser rod as another resonator mirror, and a sum frequency of an oscillation laser beam and a semiconductor laser beam is extracted.

Further, the third laser diode pumped solid laser of the present invention is a laser diode pumped solid laser in which a solid laser rod doped with a rare earth such as Nd and having an optical wavelength conversion function is pumped by a semiconductor laser as described above. An optical element such as an etalon or a wave plate having a function of stabilizing the power of the wavelength-converted wave is adhered and integrated between two solid-state laser rods, and the outer end faces of these solid-state laser rods are used as resonator mirrors. It is characterized in that the sum frequency of the oscillation laser beam and the semiconductor laser beam is extracted.

Further, the fourth laser diode pumping solid laser of the present invention is a laser diode pumping solid laser in which a solid laser rod doped with a rare earth such as Nd and having a light wavelength conversion function is pumped by a semiconductor laser as described above. A plurality of optical elements such as an etalon and a wavelength plate having a function of stabilizing the power of the wavelength-converted wave are adhered to one or more solid-state laser rods to be integrated, and one of the end faces of these optical components is A resonator is configured as a resonator mirror, and a sum frequency of an oscillation laser beam and a semiconductor laser beam is extracted by the resonator.

As the solid laser rod, a normal Self-Freque
material called ncy-Doubling Crystal, namely the aforementioned NYAB, Nd: Mg O: Li Nb O 3, Nd: it can be used PNP like. In addition, KTP, β-BBO, Li B ₂
It is also possible to use a nonlinear optical material for wavelength conversion in which a rare earth element such as Nd is doped into O ₃ , KNb O ₃ or chalcopyrite semiconductor. Particularly, KTP has a large nonlinear optical constant and a large allowable temperature range and allowable angle range, so that high wavelength conversion efficiency can be realized.

Furthermore, as represented by Nd: PNP, NPN (N- (4-
Nitrophenyl) -L-prolinol), NPAN (N-
(4-nitrophenyl) N-methylaminoacetonitrile), PRA (3,5-
A material obtained by doping an organic nonlinear optical material such as dimethyl-1- (4-nitrophenyl) pyrazole with a rare earth element can also be used. In particular, the PRA has a larger nonlinear optical constant than the KTP, and has a large allowable temperature range, so that a high wavelength conversion efficiency can be realized.

By using these solid-state laser rods as resonators at both end surfaces, the number of parts is reduced, the number of processed and polished surfaces and the number of coated surfaces are only two, and the number of laser oscillation beam absorption media is also one. Internal loss can be reduced. As a result, the internal power of the oscillating laser beam increases, and the wavelength conversion efficiency is greatly improved. In addition, the number of longitudinal modes is reduced because the resonator length is several mm,
As a result, a single mode can be achieved, longitudinal mode competition via the nonlinear optical crystal is eliminated, and the power of the sum frequency can be stabilized.

In addition, even if the power of the sum frequency is forcibly stabilized by integrating the optical element into the solid-state laser rod, the input mirror and the output mirror are eliminated, so that the oscillation laser due to absorption, scattering, and reflection is removed. The internal loss of the beam is reduced. As a result, the internal power of the oscillating laser beam increases, and the wavelength conversion efficiency is greatly improved. And it is of course possible to stabilize the power.

Further, the efficiency when a sum frequency of the semiconductor laser beam and the solid-state laser oscillation beam is generated is lower than the efficiency of the second harmonic because the power level of the semiconductor laser beam is low, and is not practical. However, in the present invention, the internal power of the oscillating laser beam is reduced by reducing its internal loss, and as a result, it is possible to increase the efficiency even in the case of sum frequency generation.

In the laser diode pumped solid-state laser of the present invention, preferably, a single transverse mode, single longitudinal mode semiconductor laser is used as the semiconductor laser for pumping. In the present invention, since the internal loss can be extremely reduced as described above, sufficient wavelength conversion efficiency can be obtained even when pumping with a small power by using these semiconductor lasers. Furthermore, since these single transverse mode and single longitudinal mode semiconductor laser beams have a spectral line width of 0.1 nm or less, which is narrower than the above-mentioned broad area lasers and array lasers, they are sufficiently absorbed by solid-state lasers, The laser oscillation efficiency can be increased, and thus the energy use efficiency can be improved. Furthermore, unlike the case of using an array laser, the light can be focused to the diffraction limit, so that the mode matching between the pumping light and the oscillating laser light is improved, and from that point, the oscillation efficiency can be improved. In addition, in the case of sum frequency generation, the sum frequency of the array laser light and the oscillation laser beam cannot be focused well because the beam of the array laser light is not a diffraction-limited beam. With a single transverse mode laser, it is possible to obtain a diffraction limited beam, and it is possible to sufficiently focus light.

As described above, according to the present invention, a compact and highly efficient laser diode pumped solid-state laser is provided.

(Embodiment) Hereinafter, the present invention will be described in detail based on an embodiment shown in the drawings.

FIG. 1 shows a laser-pumped solid-state laser according to a first embodiment of the present invention. In this laser diode pumped solid-state laser,
An LD (phased array laser) 41 that emits a laser beam 40 as pumping light is used. This LD
41 emits a laser beam 40 with a wavelength of 804 nm. A beam splitter 42 is disposed between the collimator lens 23 and the condenser lens 24. The beam splitter 42 is collimated by another collimator lens 44 emitted from another LD (single longitudinal mode laser) 43. Wavelength 830n
m laser beam 45 is incident. The laser beam 45 is multiplexed with the laser beam 40 as pumping light by the beam splitter 42 and is incident on the NYAB rod 13. The LDs 41 and 43 are each a Peltier element 14
The temperature is controlled to a predetermined temperature by a temperature control circuit (not shown).

The laser beam 45 having a wavelength λ ₁ = 830 nm incident on the NYAB rod 13 and the oscillation beam 46 of the NYAB rod 13 having a wavelength λ ₂ = 1062 nm are converted by the NYAB rod 13 into a wavelength λ ₃ =
The wavelength is converted to a sum frequency 47 of 466 nm. NYAB rod 13
Is cut so that TYPEI angular phase matching is established.

The NYAB rod 13 has a wavelength 1062 on both end surfaces 13a and 13b.
The reflective coating is applied to the
The oscillation laser beam 46 of nm is confined and oscillates. In addition, the wavelength 8
AR coating is applied to 04 nm and 830 nm, and an AR coating is applied to the output end face 13b for a wavelength of 466 nm.

In this way, the 1 W semiconductor laser beam 40 and 10
From the semiconductor laser beam 45 of 0 mW, a sum frequency 47 of 1 mW was obtained.

Further, as in the second embodiment shown in FIG. 2, the wavelength λ ₁ =
Pumped by a semiconductor laser beam 40 of 804 nm, the sum frequency 48 of the semiconductor laser beam 40 and the oscillation laser beam 46 of the NYAB rod 13 having a wavelength λ ₂ = 1062 nm
(Wavelength λ ₃ = 459 nm).

As described above, NYA is a Self-Frequency-Doubling Crystal.
While the B crystal has been described as an example, in the present invention, Nd Other crystals: Mg O: Li Nb O ₃ and Nd: KTP, Nd: can be used in the PNP and the like as well. These materials
In some cases, the NYAB crystal has a nonlinear optical constant larger than that of the NYAB crystal. Therefore, the sum frequency can be obtained more efficiently by using them.

In order to stabilize the power of the sum frequency, the third
As shown in the figure, the wavelength plate 2 such as a λ / 4 plate is
5 and the NYAB rod end face 13b as shown in FIG.
The etalon plate 22 may be adhered to the first, and the wavelength plate 25 may be further adhered thereon. Further, as shown in FIG. 5, an etalon plate 22 is attached between the two NYAB rods 13 and 13 to integrate the three elements, or as shown in FIG. Etalon plate between 13
It is also possible to adopt a configuration in which the wavelength plate 25 is adhered to the outer end surfaces of the NYAB rods 13 and 13 and the five elements are integrated.

The resonator in each of the above cases can be configured by applying the same coating to both end faces of the element as in the first embodiment.

Further, in the above embodiments, only the 1 μm band of the Nd oscillation line has been described. However, in the laser diode pumped solid-state laser of the present invention, the internal loss can be reduced. Oscillation in the 1.3 μm band is also possible, and a sum frequency of the oscillation beam and the semiconductor laser beam can be efficiently obtained.

Further, as described in each embodiment, in order to stabilize the power, the temperature of the crystal of the laser medium can be controlled to suppress the longitudinal mode hop, but in the case of the present invention, the cavity length can be extremely short, so that In addition, temperature control becomes easy, and power instability due to a change in ambient temperature can be greatly improved.

(Effect of the Invention) As described in detail above, the laser diode pumped solid-state laser of the present invention uses a solid-state laser rod having a wavelength conversion function as a resonator, or integrates an optical element with the solid-state laser rod to form a resonator. Because
It is possible to increase the internal power by reducing the internal loss, thereby improving the wavelength conversion efficiency, and to obtain an extremely high-intensity and high-efficiency short-wavelength laser light. In particular, sum frequency generation, which was conventionally low in efficiency, can be realized with high efficiency.

In the laser diode-pumped solid-state laser of the present invention, the wavelength conversion efficiency is increased as described above, so that the single transverse mode, which has a relatively low output at present,
Even if a single longitudinal mode semiconductor laser is used as a pumping source, it is possible to obtain a short-wavelength laser having sufficiently high intensity. Thus, if a single transverse mode or single longitudinal mode semiconductor laser is used as the pumping source, the oscillation efficiency of the solid-state laser is increased, and in this case, the energy use efficiency is particularly increased.

In addition, even if a relatively low-power semiconductor laser is used as a pumping source as described above, a sufficiently high-intensity short-wavelength laser can be obtained. When a sum frequency of the same light intensity is obtained, a semiconductor laser with lower output and lower cost can be used, and the above-mentioned solid-state laser rod can be used as a resonator to reduce the size and the number of parts. Therefore, a low-cost and ultra-compact solid-state laser can be realized.

Furthermore, when a sum frequency is generated by the laser diode-pumped solid-state laser of the present invention, it is possible to focus light to the diffraction limit, which has been difficult in the past.

[Brief description of the drawings]

1 and 2 are schematic side views showing laser diode pumped solid state lasers according to the first and second embodiments of the present invention, respectively. FIGS. 3, 4, 5 and 6 are solid state laser rods and optical elements according to the present invention. It is a schematic side view which shows the example of the combination state of. 13… NYAB rod, 13a, 13b… Rod end face 14… Peltier element, 22… Etalon plate 23, 44… Collimator lens, 24… Condenser lens 25 …… Wave plate, 40, 45… Laser beams 41, 43: Semiconductor laser, 46: Solid laser oscillation beam 42: Beam splitter, 47, 48: Sum frequency

Continuation of the front page (56) References JP-A-64-62621 (JP, A) JP-A-64-28879 (JP, A) JP-A-2-2194 (JP, A) JP-A-3-505948 (JP) , A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01S 3/094 H01S 3/109 H01S 3/08 H01S 3/06

Claims (5)

(57) [Claims] A rare earth element such as neodymium is doped,
In a laser diode pumped solid-state laser in which a solid-state laser rod having an optical wavelength conversion function is pumped by a semiconductor laser, both end faces of the solid-state laser rod are used as resonator mirrors, and the sum frequency of the oscillating laser beam and the semiconductor laser beam is adjusted. Laser diode pumping solid-state laser characterized by taking out. 2. A rare earth element such as neodymium is doped,
In a laser diode pumping solid-state laser that pumps a solid-state laser rod having a light wavelength conversion function with a semiconductor laser, an etalon or a wave plate having a function of stabilizing the power of the wavelength-converted wave is provided on one end surface of the solid-state laser rod. An optical element is adhered and integrated, and one side of the optical element is used as a resonator mirror of a solid-state laser, and the other end of the solid-state laser rod is used as another resonator mirror to form a resonator. A laser-diode-pumped solid-state laser characterized by extracting a sum frequency of a laser beam and a semiconductor laser beam. 3. A rare earth element such as neodymium is doped,
In a laser diode pumped solid-state laser that pumps a solid-state laser rod having an optical wavelength conversion function with a semiconductor laser, an optical element such as an etalon or a wave plate having a function of stabilizing the power of the wavelength-converted wave is used as two solid-state laser rods. A laser diode-pumped solid-state laser characterized in that the solid-state laser rods are integrated by bonding the outer end faces of these solid-state laser rods to resonator mirrors, thereby extracting a sum frequency of an oscillating laser beam and a semiconductor laser beam. 4. A rare earth element such as neodymium is doped,
In a laser diode pumped solid-state laser that pumps a solid-state laser rod having an optical wavelength conversion function with a semiconductor laser, a plurality of optical elements such as an etalon and a wave plate having a function of stabilizing the power of the wavelength-converted wave are provided. Alternatively, affixed to and integrated with a plurality of solid-state laser rods, one end face of these optical components is used as a resonator mirror to form a resonator, and the sum frequency of the oscillation laser beam and the semiconductor laser beam is extracted. Features laser diode pumped solid-state laser. 5. The semiconductor laser according to claim 1, wherein a semiconductor laser for obtaining a sum frequency is different from a semiconductor laser in which a laser beam is incident into a resonator of a solid-state laser. A laser diode-pumped solid-state laser as described in the item.