CN212721990U

CN212721990U - Laser crystal thermal focus measuring device

Info

Publication number: CN212721990U
Application number: CN202021629869.XU
Authority: CN
Inventors: 陈政; 张吉生; 罗薇; 傅立斌
Original assignee: Acculasers Co ltd
Current assignee: Acculasers Co ltd
Priority date: 2020-08-07
Filing date: 2020-08-07
Publication date: 2021-03-16
Anticipated expiration: 2030-08-07

Abstract

The utility model discloses a measuring device of laser crystal thermal focus, aiming at the problem of low precision of the existing measuring method of laser crystal thermal focus, a pumping source, a laser crystal, an output mirror and a facula detector are coaxially arranged in sequence; the dichroic mirror is arranged between the pumping source and the laser crystal and is obliquely arranged at an angle of 45 degrees relative to the coaxial axis; arranging a total reflection mirror below the dichroic mirror and parallel to the coaxial axis; the total reflection mirror and the output mirror are plane mirrors, the total reflection mirror and the output mirror form a critical resonant cavity, and the laser crystal is located in the critical resonant cavity. Two plane mirrors are adopted to form a critical resonant cavity, and a laser crystal is arranged at the central position of the critical resonant cavity, so that the influence of a high-level mode on the measurement result of the thermal focus of the laser crystal is effectively eliminated, and the measurement precision is improved.

Description

Laser crystal thermal focus measuring device

Technical Field

The utility model belongs to the technical field of laser detection, especially, relate to a measuring device of laser crystal thermal focus.

Background

Solid-state laser technology has gained popularity in the sixties of the last century, and with the development of resonant cavity technology and laser materials, solid-state lasers have been used in a variety of ways in various fields.

In a solid laser, the laser crystal and the resonator are the main considerations, especially the laser crystal is the main one, and the thermal focus generated by the crystal directly affects the stability and other properties of the resonator. Therefore, accurately measuring the thermal focal length of the laser crystal is a critical step in the design of solid state lasers.

However, the current measurement mode mainly includes a stable cavity method or a direct measurement method, and the method causes more factors caused by errors, obtains a larger range of results, and is not suitable for accurate measurement.

SUMMERY OF THE UTILITY MODEL

The utility model aims at providing a measuring device of laser crystal heat focus can effectively eliminate the influence of senior mode to laser crystal heat focus measuring result, improves measurement accuracy.

In order to solve the above problem, the technical scheme of the utility model is that:

a device for measuring the thermal focal length of a laser crystal comprises: the device comprises a pumping source, a dichroic mirror, a total reflection mirror, a laser crystal, an output mirror and a light spot detector;

the pumping source, the laser crystal, the output mirror and the light spot detector are coaxially arranged in sequence;

the dichroic mirror is arranged between the pumping source and the laser crystal and is obliquely arranged at an angle of 45 degrees relative to the coaxial axis;

the total reflection mirror is arranged below the dichroic mirror and is parallel to the coaxial axis;

the total reflection mirror and the output mirror are plane mirrors, the total reflection mirror and the output mirror form a critical resonant cavity, and the laser crystal is located in the critical resonant cavity.

According to an embodiment of the present invention, the laser crystal is disposed at a central position of the critical resonant cavity.

According to an embodiment of the present invention, the measuring device for the thermal focus of the laser crystal further comprises an attenuating mirror;

the attenuation mirror is arranged between the output mirror and the light spot detector and is coaxial with the output mirror.

According to an embodiment of the present invention, the device for measuring the thermal focus of the laser crystal further comprises a focusing lens;

the focusing lens is arranged between the attenuating mirror and the light spot detector and is used for measuring the quality of the laser beam by adopting a lens conversion method.

According to the utility model discloses an embodiment, the attenuator is NDfilter, the facula detector is the CCD detector.

The utility model discloses owing to adopt above technical scheme, make it compare with prior art and have following advantage and positive effect:

1) the utility model discloses a measuring device of laser crystal thermal focus in an embodiment to the problem that current laser crystal thermal focus measuring method precision is low, adopts two level crossings to constitute critical resonant cavity, locates laser crystal the central point of this critical resonant cavity puts, effectively eliminates advanced mode to laser crystal thermal focus measuring result's influence, improves measurement accuracy.

2) The utility model relates to an embodiment's measuring device of laser crystal focus sets up the attenuator between output mirror and facula detector, can reduce the laser strength who sees through the output mirror, prevents that laser strength from excessively surpassing the saturation light intensity of facula detector and influencing the measuring result.

3) The utility model discloses a measuring device of laser crystal heat focus in the embodiment sets up focusing lens between attenuator and facula detector, can realize the quality that lens transform method measured laser beam, further eliminates the influence of senior mode to laser crystal heat focus measuring result, measures laser heat focus more accurately.

Drawings

Fig. 1 is a schematic structural diagram of a device for measuring a thermal focus of a laser crystal according to an embodiment of the present invention;

fig. 2 is an equivalent schematic diagram of a critical resonant cavity according to an embodiment of the present invention;

fig. 3 is a schematic diagram of an embodiment of the invention using a focusing lens.

Description of reference numerals:

1: a total reflection mirror; 1.1: fully-reflecting the film; 2: a dichroic mirror; 3: a laser crystal; 4: an output mirror; 4.1: a partially permeable membrane; 5: a pump source; 6: an attenuating mirror; 7: a light spot detector; 8: a focusing lens.

Detailed Description

The following describes the measurement apparatus for the thermal focus of a laser crystal according to the present invention in further detail with reference to the accompanying drawings and specific embodiments. The advantages and features of the present invention will become more fully apparent from the following description and appended claims.

Example one

The utility model discloses to the problem that current laser crystal hot focal length measuring method precision is low, provide one kind and can effectively eliminate the influence of high order mode to laser crystal hot focal length measuring result, improve measuring accuracy's laser crystal hot focal length's measuring device.

Referring to fig. 1, the device for measuring the thermal focal length of the laser crystal includes a pump source 5, a dichroic mirror 2, a total reflection mirror 1, a laser crystal 3, an output mirror 4, an attenuating mirror 6, and a spot detector 7. Wherein, the pumping source 5, the laser crystal 3, the output mirror 4, the attenuator 6 and the light spot detector 7 are coaxially arranged in sequence; the dichroic mirror 2 is arranged between the pumping source 5 and the laser crystal 3 and is obliquely arranged at an angle of 45 degrees relative to the coaxial axis; the holophote 1 is arranged below the dichroic mirror 2 and is parallel to the coaxial axis.

In order to improve the measurement accuracy of the laser thermal focal length, a critical cavity is designed for the laser crystal. Because the oscillation starting condition of the critical cavity is more rigorous than that of a stable cavity (such as a confocal cavity) consisting of concave mirrors, the loss of a high-order mode in the cavity is increased and oscillation cannot be started, so that the critical resonant cavity only outputs a basic mode, the quality of light spots is improved, and the precision of measuring the focal length of the laser crystal thermal lens is improved.

Specifically, as shown in fig. 2, in this embodiment, a critical resonant cavity is formed by two plane mirrors, that is, a critical resonant cavity is formed by a total reflection mirror 1 and an output mirror 4, and both the total reflection mirror 1 and the output mirror 4 are plane mirrors. In practical applications, the holophote 1 may be a mirror with a reflectivity of 99% or more for a specific wavelength, and 1064nmHR 99%, 0 ° may be used. And the output mirror 4 is a partially transmissive mirror with a reflectivity of 90%.

In the critical cavity, the laser crystal 3 is located at the center of the critical cavity, so that stable output of the basement membrane can be obtained. The laser crystal 3 may be Nd: YVO4 or Nd: YAG, etc.

Because the intensity of the laser penetrating through the output mirror 4 is relatively large, the attenuation mirror 6 is arranged between the output mirror 4 and the light spot detector 7, the intensity of the laser penetrating through the output mirror is reduced, and the situation that the intensity of the laser exceeds the saturated light intensity of the light spot detector to influence the measurement result is prevented. The attenuator 6 may be an NDfilter and the spot detector 7 is an instrument for observing the size and mass of the spot, such as a CCD detector. The dichroic mirror 2 reflects 1064nm and transmits 878nm (or 808nm), and the pumping source 5 is an LD laser.

The working process of the device for measuring the thermal focal length of the laser crystal in the present embodiment is briefly described as follows:

the pumping source 5 is started, pumping light is emitted to the laser crystal 3 through the dichroic mirror 2, the crystal 3 is excited by the pumping light, particle number inversion is generated to generate laser, and meanwhile, a thermal lens effect is generated due to the pumping light. The laser oscillates in a critical cavity consisting of the all-mirror 1 and the output mirror 4, which can eliminate most of the higher order modes. The output mirror 4 outputs laser light, and the laser light reaches a light spot detector 7 through an attenuation mirror 6.

The following briefly describes the steps of measuring the thermal focus of laser by using the apparatus for measuring the thermal focus of laser crystal in this embodiment:

step one, building a structure as shown in fig. 1, starting a pumping source 5, adjusting to a specified output power, and forming a stable laser crystal thermal lens in the laser crystal 3, wherein the standard is based on the stable laser output for three minutes.

Step two, placing the attenuation mirror 6 and the light spot detector 7 to enable the laser power after attenuation to be smaller than the saturation power of the light spot detector 7, and recording the distance z1 from the target surface position of the light spot detector 7 to the part of the output mirror 4 penetrating through the membrane 4.1 and the laser light spot radius omega₁Then the spot detector 7 is moved to a position where z1 is spaced apart by Δ z, and the magnitude of Δ z and the laser spot radius ω are recorded₂。

And step three, calculating the laser beam waist spot radius on the partially-transmitting film 4.1 according to the following formula. The calculation method is as follows, wherein, lambda is the laser wavelength, omega₀Is the size of the waist of the laser beam partially transmitted through the film 4.1.

Here, it should be noted that, with respect to the laser propagation direction, when the z1+ Δ z position is located on the left side of the z1 position, Δ z takes a negative value.

And step four, after the laser beam waist radius is obtained, the numerical value of the laser wavefront curvature R at the laser crystal 3 can be further obtained. The calculation is as follows, where L is the length of the critical cavity, i.e. the distance from the totally reflecting film 1.1 to the partially transmitting film 4.1.

Since the critical resonant cavity is a symmetric cavity, the focal length f of the laser crystal 3 is calculated as follows,

in performing the above measurement steps, the following points need to be noted:

1. during the measurement, the position of z1 needs to be collected, and the distance from the part of the film 4.1 to the target surface position of the spot detector 7 can be measured by using a ruler, and meanwhile, the thickness of the output mirror 4 is multiplied by the difference between the refractive index of the material and the refractive index of air, so that the measured length is the distance from the laser to actually propagate to z 1.

2. In the above calculation, the critical cavity length L is measured, and the value can be measured by measuring the distance from the total reflection film 1.1 to the partially transparent film 4.1 in the total reflection mirror 1 by using a ruler, and then subtracting (1-n)_c) m, the result is the value of the critical cavity length L shown in fig. 2. Wherein n is_cM is the actual length of the laser crystal 3, which is the refractive index of the laser crystal 3.

Example two

Compared with the first embodiment, the difference of the present embodiment is that a focusing lens 8 is arranged between the attenuation mirror 6 and the spot detector 7 for realizing the measurement of the quality M of the laser beam by the lens conversion method²As shown in fig. 3.

The device for measuring the thermal focal length of the laser crystal in the embodiment can effectively eliminate the measurement influence of a high-order mode on the quality of a laser beam. Since the structure of the device for measuring the thermal focal length of the laser crystal in this embodiment is similar to that in the first embodiment, further description is omitted here.

The following briefly describes the steps of measuring the laser beam quality by using the device for measuring the thermal focal length of the laser crystal in the present embodiment:

step one, building a structure as shown in fig. 1, starting a pumping source 5, adjusting to a specified output power, and forming a stable laser crystal thermal lens in the laser crystal 3, wherein thermal equilibrium can be achieved in the crystal in about 10 minutes generally.

Step two, after the attenuating mirror 6 is placed, the quality M of the laser beam is measured by using a lens conversion method². When the focusing lens 8 is used, the focal length of the selected lens is not too large. The spot radii omega at the left and right focal points of the focusing lens 8 are measured separately_f1And ω_f2As shown in fig. 3. Note that the spot detector 7 should not be made to appear saturated with spots. The beam mass M is then calculated using the following equation²Value of, wherein_f1Is the radius of the spot at the left focus, omega_f2Is the spot radius at the right focus, and f is the focal length of the focusing lens 8.

Step three, removing the focusing lens 8, placing the light spot detector 7, enabling the laser power passing through the attenuation mirror 6 to be smaller than the saturation power of the light spot detector 7, and recording the distance z1 from the target surface position of the light spot detector 7 to the part of the output mirror 4 penetrating through the film 4.1 and the light spot radius omega of the light spot detector₁Then the spot detector 7 is moved to a position spaced from z1 by Δ z, and the magnitude of Δ z and the laser spot radius ω are recorded₂。

Step four, calculating the laser beam waist radius omega on the partial transmission film 4.1 by using the following formula₀. Wherein λ is the laser wavelength.

Here, it should be noted that, with respect to the laser propagation direction, when the z1+ Δ z position is located on the left side of the z1 position, the value of Δ z is a negative value; since the laser beam contains high order modes, the square of the two beam radii is divided by M²The value is then the fundamental mode spot radius of the actual beam.

And step five, after the laser beam waist radius is obtained, the laser wavefront numerical value at the laser crystal 3 can be further obtained, and the calculation mode is as follows. Wherein, L is the length of the critical resonant cavity, namely the distance from the total reflection film 1.1 to the partial transmission film 4.1.

Since the critical resonant cavity is a symmetric cavity, the numerical calculation of the laser crystal 3 is as follows.

During the measurement, z1 and L are both measured in the same manner as in embodiment 1. In addition, when the high-order mode of the laser beam is not only a circular spot, but also a spot of other patterns, an adjustable small hole needs to be added near the laser crystal 3 in the resonant cavity to suppress the generation of additional high-order mode. However, although the method is adopted to reduce the high-order mode, the method still needs to be executed according to the above measurement steps, and the influence of the residual high-order mode on the measurement result is avoided.

The embodiments of the present invention have been described in detail with reference to the accompanying drawings, but the present invention is not limited to the above embodiments. Even if various changes are made to the present invention, the changes are still within the scope of the present invention if they fall within the scope of the claims and their equivalents.

Claims

1. A device for measuring the thermal focal length of a laser crystal is characterized by comprising: the device comprises a pumping source, a dichroic mirror, a total reflection mirror, a laser crystal, an output mirror and a light spot detector;

2. The apparatus for measuring the thermal focus of a laser crystal as defined in claim 1, wherein said laser crystal is disposed in the center of said critical cavity.

3. The apparatus for measuring the thermal focal length of a laser crystal of claim 1, further comprising an attenuating mirror;

4. The apparatus for measuring the thermal focal length of a laser crystal of claim 3, further comprising a focusing lens;

5. The apparatus for measuring the thermal focus of a laser crystal according to claim 4, wherein the attenuator is an ND filter, and the spot detector is a CCD detector.