RU2304332C2 - Micro-laser - Google Patents

Abstract

FIELD: laser engineering, in particular, solid lasers, possible use in medicine, image output devices, analytical and other equipment.

SUBSTANCE: micro-laser contains pumping source in form of laser diode, collimator and/or focusing optics, resonator. Focusing optics is made in form of cylindrical or spherical or gradient lens. Resonator consists of input and output mirrors and an active element positioned between them. Between mirrors and the active element, two plates are mounted additionally made of heat-conductive material which does not absorb laser radiation, with apertures in the center. Plates, active element and mirrors are made flat-parallel. Resonator elements are in tight contact with each other. Input mirror may be applied directly to the surface of active element. Between active element and output mirror, a plate is mounted. Second plate is positioned behind the active element.

EFFECT: creation of compact micro-laser structure, in which adjustment of resonator by method of correction of thermal lens oriented in active element is realized by passive elements.

8 cl, 14 dwg, 3 graphs

Description

The invention relates to the field of laser technology, in particular to solid-state lasers, and may be applicable in medicine, image output devices, analytical and other equipment.

It is known that during thermal expansion of an active laser element, due to the heat generated in it during laser operation, its surfaces bend, which work like lenses called thermal, and if optical mirror coatings are applied to the surface of the active laser element, they are curved mirrors .

When certain conditions are created that allow thermal lenses to be corrected, it is possible to obtain a gain in the output power and ensure the mode selectivity of laser radiation.

A laser is known in which a laser deformable mirror is used as an active correction of a thermal lens of a solid-state laser (G.V. Vdovin et al. Active correction of a thermal lens of a solid-state laser and the use of a cavity of controlled configuration. “Quantum Electronics”, 20, No. 2, 1993) .

The disadvantages of the known laser are the complexity of manufacturing a deformable mirror and controlling its curvature pressure.

The closest in technical essence to the proposed design is a microchip laser in which the resonator consists of an input and output mirrors and an amplifying medium (active element) located between them, as well as at least one nonlinear crystal (see US patent No. 5402437, C. H01S 003/094, 1995).

As an amplifying medium (active element) in a known design using a laser crystal

In the known construction, the cavity length is chosen such that the gain bandwidth of the amplifying medium is less than or nearly equal to the frequency spacing of the resonator and such that the frequency of the resonator mode falls within the gain bandwidth.

A microchip laser may contain a nonlinear optical material for generating new laser wavelengths, which are installed inside or outside the resonator.

Alternatively, the microchip laser can be tuned, for example, thermally or by applying longitudinal or transverse voltage to the resonator frequency.

A microchip laser is optically pumped with a semiconductor laser or a laser matrix.

The disadvantages of the design of the known microchip laser are:

- the need for bench tuning of the length of the resonator in the operating mode by additional alignment of the input and output mirrors of the resonator spaced apart by the required distance;

- the complexity of the design when using the method of creating a longitudinal or transverse stress in the active element, because this method requires the use of additional precision mechanical or piezoelectric devices;

- the complexity of manufacturing a compact heat-insulating device in the design of the temperature adjustment of the microlaser due to the need to maintain the temperature with high accuracy, which in real conditions of microlaser operation at various ambient temperatures is difficult to carry out without reliable and cumbersome thermal insulation.

The technical task of the invention is the creation of a compact microlaser design in which the substring of the resonator by the correction of the thermal lens induced in the active element is carried out by passive elements located outside and / or inside the resonator.

For this, it is necessary to introduce additional passive elements into the resonator of the proposed microlaser design, which will allow forming a radially symmetric temperature gradient on a limited surface of the active element, in which a certain volume of the active element is localized and in which a thermal lens is formed due to the heat released in the active element and the so-called thermal waveguide that helps stabilize the transverse TEM ₀₀ mode.

The technical result in the present invention is achieved by creating a microlaser containing a pump source in the form of a laser diode, a collimator and / or focusing optics, made in the form of at least one or a cylindrical, or spherical, or gradient lens, a resonator, consisting of input and output mirrors, and an active element located between them, in which, according to the invention, two plates of non-absorbing laser radiation are additionally installed between the mirrors and the active element in this case, the plates, the active element and the mirrors are made plane-parallel, and all of the listed resonator elements are in close contact with each other.

The input mirror in the form of an optical coating can be located directly on one of the plane-parallel sides of the active element, then one of the heat-conducting plates is installed between the output mirror and the active element, and the second heat-conducting plate is installed behind the active element, while the heat-conducting plates, the active element, and the output mirror are in close contact.

For pulsed operation of the microlaser, a passive shutter made in the form of a plane-parallel plate with optical coatings can be installed in the resonator.

To obtain the second and higher harmonics of the laser radiation, a nonlinear element made in the form of a plane-parallel plate having optical coatings can be installed in the microlaser resonator.

For the pulsed operation of the microlaser at the second and higher harmonics of the laser radiation, a passive shutter and a nonlinear element made in the form of plane-parallel plates having optical coatings can be installed in the microlaser resonator.

The heat-conducting plates with holes provide an effective heat sink from the surface of the active element, since they are in close contact with it, while simultaneously providing the possibility of forming a thermal lens only in the aperture of the holes, the correction of the thermal lens is carried out by selecting the length of the heat-conducting plates and the diameter of the holes in them.

Changing the length of the plates / plate changes the length of the resonator and the pulse duration of the microlaser operating in the mode of Q-switching.

Tight connection with each other of plane-parallel active element, heat-conducting plates and mirrors ensures the manufacture of a resonator that does not require additional alignment, since the listed elements assembled in close contact form a plane-parallel resonator.

The choice of non-absorbing laser radiation material for the manufacture of wafers is due to the fact that when aligning the resonator with a pump diode in the operating mode, it eliminates the evaporation of this material when laser radiation hits the edge of the wafer, which leads to damage to the optical coatings in the resonator, and eliminates the possibility of marriage in serial production.

The invention is also characterized in that the pump source and the resonator can be installed on at least one thermoelectric refrigerator, which allows you to maintain the necessary temperature for the pump source and stable operation of the resonator.

Conducted patent studies have shown that technical solutions with the indicated set of essential features in similar designs of microlasers are not known, i.e. the proposed technical solution meets the criterion of "novelty."

In the analysis of well-known analogues and prototype, no proposal was found with a combination of essential features set forth in the claims, which implies that for specialists involved in microlasers, they do not explicitly follow from the prior art and, therefore, meet the criteria of the invention of "inventive step".

We believe that the information set forth in the application materials is sufficient for the practical implementation of the invention.

The invention is illustrated by the following description of the microlaser and drawings with a reflection of the relative position of the elements of the resonator, where:

- figure 1 shows the General scheme of the microlaser;

- figure 2 shows the General scheme of the microlaser, in the cavity of which the input mirror is deposited directly on the surface of the active element, one of the plates of non-absorbing laser radiation heat-conducting material is installed between the output mirror and the active element, and the second plate behind the active element;

- figure 3 shows a resonator circuit of a microlaser in which a passive shutter is installed between a non-absorbing laser radiation heat-conducting plate and an output mirror;

- figure 4 shows a diagram of the resonator microlaser, in which the output mirror is applied directly to the polished surface of the passive shutter;

- figure 5 shows a resonator circuit of a microlaser in which a plane-parallel nonlinear element is installed between a non-absorbing laser radiation heat-conducting plate and an output mirror;

- figure 6 shows the resonator circuit of the microlaser, in which the output mirror is applied directly to the nonlinear element;

- Fig.7 shows a resonator circuit of a microlaser in which a passive shutter and a nonlinear optical crystal are installed between a non-absorbing laser radiation heat-conducting plate and an output mirror;

- Fig. 8 shows a resonator circuit of a microlaser, in which, in contrast to Fig. 7, the output mirror is applied directly to the non-linear element;

- figure 9 shows a resonator circuit of a microlaser, in which, in contrast to figure 2, between the output mirror and the heat-conducting plate, a passive shutter is installed;

- figure 10 shows a resonator circuit of a microlaser, in which, in contrast to figure 9, the output mirror is applied to a passive shutter;

- figure 11 shows a resonator circuit of a microlaser, in which, in contrast to figure 2, a non-linear element is installed between the output mirror and the heat-conducting plate;

- Fig. 12 shows a resonator circuit of a microlaser, in which, in contrast to Fig. 11, the output mirror is deposited on a nonlinear optical crystal;

- Fig.13 shows a resonator circuit of a microlaser, in which, in contrast to Fig.2, a passive shutter and a nonlinear element are installed between the output mirror and the heat-conducting plate;

- on Fig shows a resonator circuit of a microlaser, in which, in contrast to Fig.13, the output mirror is deposited on a nonlinear optical crystal;

on Fig (graph 1) shows the profile of the laser beam of a microlaser, in the resonator of which there are no heat-conducting plates with holes;

in Fig.16 (graph 2) shows the profile of the laser beam of a microlaser, the resonator of which is assembled according to the design shown in Fig.1 with a hole diameter of 1.5 mm in the heat-conducting plates;

- Fig. 17 (graph 3) shows the laser beam profile of a microlaser, the resonator of which is assembled according to the structure shown in Fig. 1 with a hole diameter of 0.7 mm in the heat-conducting plates.

The microlaser contains a pump source in the form of a laser diode 1, a collimator or focusing optics 2, made in the form of at least one or a cylindrical, or spherical, or gradient lens, and a resonator.

The resonator comprises an input mirror 4, an active element 5, an output mirror 6, two plates 7 and 8 of non-absorbing laser radiation heat-conducting material with holes 9.

The plates 7 and 8, the active element 5 and the input 4 and output 6 of the mirror are plane parallel and are in close contact with each other.

Depending on the selected active element, for example, a laser crystal or activated glass, its generation and thermo-optical characteristics, material is selected for non-absorbing laser radiation heat-conducting plates 7 and 8 (glass, quartz, sapphire, garnet, ceramics, etc.) and hole size 9 in them.

The relative position of the elements of the resonator microlaser may be different:

1. Each of the heat-conducting plane-parallel plates 7 and 8 of non-absorbing laser radiation heat-conducting material is installed between the input 4 or output 6 mirrors and the active element 5.

2. One heat-conducting plane-parallel plate 7 of non-absorbing laser radiation heat-conducting material is installed between the output mirror 6 and the active element 5, the second plate 8 is installed behind the active element 5 with an input mirror 4 deposited on its surface.

The microlaser can be equipped with a passive shutter 10 mounted in the resonator.

A passive shutter 10 can be installed between the non-absorbing laser radiation heat-conducting plate 7 and the output mirror 6, and a second heat-conducting plate 8 is installed between the input mirror 4 and the active element 5.

Perhaps the execution of a microlaser, in which the output mirror 6 is applied directly to the passive shutter 10.

In the proposed design of the microlaser, a nonlinear element 3 can be installed between the plane-parallel heat-conducting plate 7 and the output mirror 6.

The microlaser can be equipped with both a passive shutter 10 and a nonlinear element 3, which are located between the plane-parallel plate 7 of a non-absorbing laser radiation heat-conducting material and an output mirror 6.

In the proposed microlaser, the pump source and the resonator, if necessary, are installed on at least one thermoelectric refrigerator.

In the resonator of the proposed microlaser, the plane-parallel input mirror 4 on one side has an optical coating that is antireflective to the wavelength of the laser diode, and on the other side has a dichroic optical coating that transmits the radiation of the laser diode and a highly reflective coating at the wavelength of the active element generation.

In this case, the plane-parallel output mirror 6 on one side has an optical coating that is antireflection on the generation wavelength of the active element, and on the other side has an optical coating, which is an output mirror of the resonator having a certain transmittance at the generation wavelength.

In the resonator of the proposed microlaser, the active element 5 has on both plane-parallel optical coatings.

In the resonator of the proposed microlaser, you can optionally install a passive shutter 10 and / or non-linear element 3, made in the form of plane-parallel plates having optical coatings.

The elements of the resonator are assembled in close contact with each other depending on the circuits disclosed in figures 1-14.

The pump radiation of the laser diode 1 is focused through the optical system 2 into the resonator of the microlaser, in which the generation of laser radiation occurs.

In the proposed microlaser, plane-parallel plates 7 and 8 with holes 9 of non-absorbing laser radiation heat-conducting material provide heat removal from the surface of the active element 5, since they are in close, mechanical contact with it.

The pump radiation is absorbed through the hole 9 in the heat-conducting plate in a very small, localized volume of the active element 5.

The holes 9 of the heat-conducting plates 7 and 8 form a thermal lens (not shown) on the surface of the active element 5 bounded by the holes.

The diameter of the thermal lens and the radius of its curvature depend on the diameter of the holes 9 in the heat-conducting plates and the thermophysical characteristics of the active element and the heat-conducting plates.

For experimental verification of the proposed microlaser design, three microlasers were emitted at 1.064 μm.

As the active element 5, a plane-parallel plate of a Nd: YVO ₄ laser crystal with a length of 1.5 mm and a diameter of 3 mm was used.

Plane-parallel plates 7 and 8 of non-absorbing laser radiation heat-conducting material were made of an inactive YAG crystal. Wafers of two sizes were made: 0.3 mm long, 3 mm in diameter, a hole 9 in the center of the plate with a diameter of 1.5 mm and a length of 0.5 mm, 3 mm in diameter made in the center of the plate a hole 9 with a diameter of 0.8 mm.

The input 4 and output 6 resonator mirrors were made of plane-parallel plates and had the same characteristics as the coatings deposited on the surface of the laser crystal (not shown):

- the input mirror 4, on the one hand, had an antireflective optical coating transmitting the pump radiation of the laser diode 99% @ 808 nm, and on the other hand, a dichroic optical coating transmitting the pump radiation of the laser diode 98% @ 808 nm and reflecting 99.8% @ 1064 nm ;

- the output mirror 6 on the one hand had an optical coating reflecting laser radiation of 97% @ 1064 nm, on the other hand, an antireflection optical coating of 99% @ 1064 nm;

- the input mirror 4, deposited on the surface of the active element 5, was a dichroic coating, transmitting the radiation of a laser diode 98% @ 808 nm and reflecting 99.8% @ 1064 nm, on the other hand, an antireflection optical coating 99% @ 1064 nm.

When using external mirrors, a laser crystal was installed in the cavity with antireflective optical coatings deposited on its plane-parallel sides — 99% @ 1064 nm.

All elements of the resonator were placed in a metal case (not shown), which ensured tight contact of all elements of the resonator and to which the heat released in the active element 5 and transferred by the heat-conducting plates 7 and 8 was discharged.

In all laser experiments, a 2 W OSLAM SPL CG81 laser diode was used as a pump source.

The plane of the laser diode beam perpendicular to the emitting surface (1 × 200 μm) was collimated by a cylindrical lens with a diameter of 200 μm into an elliptical spot with dimensions: in the X directions - 200 μm, in the Y direction - 100 μm.

To assess the quality of the laser beam and the output power of the microlasers, a BeamView Analyzer laser beam profile analyzer and a Coherent Lasermate power meter were used.

In an experiment with a microlaser, without using plane-parallel heat-conducting plates with holes in the design, a laser crystal was placed between the cavity mirrors, the length of which was 3 mm. With a pump power of 1000 mW, the output laser power at 1064 nm was 310 mW.

It should be noted that the laser output at 1064 nm was unstable both in terms of amplitude and divergence, which indicates a strong mode tuning.

As follows from graph 1, component X of the laser beam has much worse quality than component Y. The reason for this is the elliptical focus of the pump. The size of the laser TEM ₀₀ mode is much smaller than the size of the component X of the pump focus; therefore, higher-order modes can also generate.

In the microlaser, the resonator design of which is shown in FIG. 1, where between the active element 5, the input mirror 4 and the output mirror 6, heat-conducting plates 7 and 8 were installed in tight contact 0.3 mm long, 3 mm in diameter, with holes 9 with diameter 1 , 5 mm, the main TEM ₀₀ mode was maintained with increasing pump power to 1000 mW despite the elliptical pump focus.

The cavity length was 2.1 mm. The output power of the laser radiation at 1064 nm was 460 mW.

The microlaser showed significantly more stable and high power output. As follows from graph 2, the laser beam has a Gaussian profile.

This is because the thermal lens formed by the holes 9 of the heat-conducting plates 7 and 8 is smaller than in a microlaser assembled without plates.

The heat-conducting plates 7 and 8 provide good conditions for the cooling of the laser crystal due to direct contact with it and the holes, a radially symmetric gradient is formed, which is confirmed by the symmetry of the laser beam, however, as in the previous experiment, a high divergence of the laser beam of 12 mrad is maintained.

Figure 3 shows the profile of the laser beam and the energy distribution in it, the design of the microlaser resonator was also assembled in figure 1, where between the active element 5, the input mirror 4 and the output mirror 6 heat-conducting plates 7 and 8 were installed in tight contact with a length of 0, 5 mm, diameter 3 mm, with holes 9 with a diameter of 0.8 mm.

The laser beam has a Gaussian profile. The main mode was maintained with increasing pump power up to 1000 mW, the output laser power was 480 mW.

Graphs 2 and 3 differ from each other by the divergence of the laser radiation and the ellipticity of the laser beam. The formed thermal lens with heat-conducting plates with holes with a diameter of 0.8 mm is much smaller than in the previous experiment with plates having holes with a diameter of 1.5 mm. The laser beam divergence in the last experiment was 6 mrad.

The obtained results confirm the effective effect of heat-conducting plates with holes on the formation of a thermal lens, which allows plates to adjust the resonator taking into account the thermal and optical characteristics of the chosen active medium.

Claims (8)

1. A microlaser containing a pump source in the form of a laser diode, a collimator and / or focusing optics, made in the form of at least one or a cylindrical, or spherical, or gradient lens, a resonator consisting of input and output mirrors and located between them active element, characterized in that two plates are additionally installed in the resonator made of non-absorbing laser radiation heat-conducting material with a hole in the center, while the plates are installed either between the mirrors and the active m element, or one plate is installed between the output mirror and the active element, and the second plate is behind the active element, on the surface of which there is an input mirror in the form of an optical coating, moreover, the plates, active element and mirrors are made plane-parallel, and all of the listed resonator elements are in close contact with each other. 2. The microlaser according to claim 1, characterized in that a passive shutter made plane-parallel is installed in the resonator between the heat-conducting plate with the hole and the output mirror. 3. The microlaser according to claim 1, characterized in that the output mirror is made directly on the passive shutter. 4. The microlaser according to claim 1, characterized in that at least one non-linear element that is plane-parallel is installed in the resonator between the heat-conducting plate with the hole and the output mirror. 5. The microlaser according to claim 4, characterized in that the output mirror of the resonator is made directly on a nonlinear element. 6. The microlaser according to claim 1, characterized in that a passive shutter and at least one non-linear element that are plane-parallel are installed in the resonator between the heat-conducting plate with the hole and the output mirror. 7. The microlaser according to claim 6, characterized in that the output mirror of the resonator is made directly on the nonlinear element. 8. The microlaser according to claim 1, characterized in that the laser diode and the resonator are mounted on at least one thermoelectric refrigerator.

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