CN102280800A - Laser thermal effect compensating system - Google Patents

Abstract

The invention provides a novel solid laser thermal effect compensating method. A thermal effect compensating system is additionally arranged in a laser oscillating cavity; the system is composed of a heat sink (3), a compensating plate (4), an annular transmissivity lens (6), a telescope (7), an optical fiber (8) and an LD (laser diode) (9); the body temperature distribution of the compensating plate can be changed precisely through regulating the cooling temperature of the heat sink, the input power of the LD or the displacement or focal length of the annular transmissivity lens, and the thermal lens effect of a laser working substance (2) can be compensated; through designing different body and surface temperature distributions of the compensating plate, the system provided by the invention can be used for compensating each stage of thermal lens effect of different lasers, such as bar-shaped, lath-shaped and side pumps, end pumps and the like; and the system has the characteristics that an optic medium capable of regulating temperature distributions dynamically and corresponding temperature control systems are inserted into a laser resonant cavity, thus the precise dynamic compensation of the laser thermal effect is realized.

Description

Laser heat effect compensating system

Technical field

The present invention relates to the photoelectron technology field.

Background technology

Laser diode pumping full-solid laser (Diode Pumped Solid-State Laser, DPSSL) be to adopt laser diode (Laser Diode, LD) or diode laser matrix (Laser Diode Array LDA) substitutes the class laser of photoflash lamp as the pumping of solid-state laser source.

The working-laser material of DPSSL is in being subjected to the lasing process of pump light effect, the part pump energy is converted into heat, its main cause has: a) between pumping band and the upper laser level, the energy difference between laser lower level and the ground state is emitted in the parent lattice with the form of heat, causes quantum loss heating; B) the transition process quantum efficiency of fluorescence is less than 1, thereby the cancellation process produces heat; C) the absorption heat of host material.Thereby at one " endogenous pyrogen " of the inner formation of the laser medium of DPSSL.

Generally need external refrigeration during laser works, thereby formed uneven Temperature Distribution.Simultaneously since various working-laser materials all the thermocolour of various degrees loose (thermal dispersion), promptly the temperature coefficient of refractive index is not a constant.

The refractive index of glass material is provided by following formula with variation of temperature:

$\mathrm{\&Delta;}{n}_{\mathrm{abs}}(\mathrm{\&lambda;},T)=\frac{n^2(\mathrm{\&lambda;},T_0)-1}{2\&CenterDot;n(\mathrm{\&lambda;},T_0)}\&CenterDot;(D_0\&CenterDot;\mathrm{\&Delta;T}+{\mathrm{<figure-callout\; id="1"\; label="D"\; filenames="HSA00000151566700011.png"\; state="\{\{state\}\}">D</figure-callout>}}_1\&CenterDot;\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="2"\; label="T"\; filenames="HSA00000151566700011.png"\; state="\{\{state\}\}">T</figure-callout>}}^2+{\mathrm{<figure-callout\; id="2"\; label="D"\; filenames="HSA00000151566700011.png"\; state="\{\{state\}\}">D</figure-callout>}}_2\&CenterDot;\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="3"\; label="T"\; filenames="HSA00000151566700011.png"\; state="\{\{state\}\}">T</figure-callout>}}^3+\frac{E_0\&CenterDot;\mathrm{\&Delta;T}+E_1\&CenterDot;\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="2"\; label="T"\; filenames="HSA00000151566700011.png"\; state="\{\{state\}\}">T</figure-callout>}}^2}{{\mathrm{\&lambda;}}^2-{\mathrm{\&lambda;}}_{\mathrm{TK}}^2})$

Wherein Δ T is relative 20 ℃ temperature change value; λ is the vacuum medium wavelength; D ₀, D ₁, D ₂, E ₀, E ₁, λ _TKTo certain material is constant.

Thereby when laser operation, the refractive index in the working substance plastid will be no longer even, and distribute axisymmetricly.Like this, light produces thermal lensing effect through out-of-date generation deviation.And along with the increase of pump power, refractive index constantly changes, and it is even more serious that thermal lensing effect becomes, and the beam quality of laser output also worsens all the more.

As can be seen, refractive index n and temperature T are not simple linear relationships from formula; Thereby the thermal lensing effect of working-laser material must comprise the high-order amount.Theory analysis shows, has relation of plane down between the radius of refractive index and dielectric rod:

n(r)＝n ₀+C ₂·r ²+C ₄·r ⁴

In the formula, C ₂, C ₄Be respectively two, four aberration coefficients of thermic spherical aberration.

In order to eliminate or reduce the influence of thermal lensing effect, the measure that present researcher has adopted has:

A) single element negative lens is inserted resonant cavity; B) design cavity resonator structure with dielectric rod as thick positive lens.These two kinds of methods can be carried out the one-level correction to thermal lensing effect.

C) utilize movably optical element; D) optical element of controlling by the translation microprocessor.These two kinds of methods can realize the first-stage dynamic compensation to different pump powers.

E) adopt the optical phase conjugation mirror; F) adopt the aspheric surface revision board, comprise diamond turning, crystallite printing and ion etching etc.These two kinds of methods can be revised the higher-order effect of thermal lens.

G) adopt the recombination laser operation material; H) adopt other low cavity structure of thermal effect, such as lasers such as lath or thin slices.These two kinds of methods can reduce or avoid thermal lensing effect.

But these methods or can only revise thermal lensing effect single order item perhaps can only static modification, and perhaps tuning difficulty is big, and perhaps cost is higher, perhaps will change cavity structure.

Summary of the invention

The present invention seeks to high-output power and high light beam quality to be satisfied simultaneously in order to improve thermal effect to the influence that the solid-state laser beam quality causes.

The present invention inserts the variable compensating plate of body refraction index profile in laser resonant cavity, the thermal lensing effect of laser is compensated.

The present invention adopts following technical scheme:

1. the thermal effect compensation system of a laser is made of temperature-compensating medium, thermal source, cooling device, optical system, and wherein, the temperature-compensating medium is used for the hot distortion effect of dynamic compensation laser beam; Thermal source and cooling device are used to generate the required Temperature Distribution of temperature-compensating medium; Optical system is used for thermal source is focused on the temperature-compensating dielectric surface.

2. according to the described thermal effect compensation of item 1 system, used temperature-compensating material is an optical filter in the system, and the luminous wave band of laser working medium is seen through, and the thermal source wave band used to bucking-out system absorbs.

3. but the laser of dynamic adjustments self Temperature Distribution, its resonant cavity comprise 1 a described temperature compensation system, and objects such as laser working medium, chamber mirror.

Compared to conventional compensation approach, the present invention has following advantage:

1. not only compensate the low order item of thermal lensing effect, and can compensate higher order term;

2. along with the increase of pump power, compensation rate can manual adjustment, thereby realizes dynamic compensation;

3. technical easy realization, tuning simple, effect is obvious, and cost is lower.

Description of drawings

Fig. 1 is the example pie graph of laser heat effect compensating of the present invention system;

Fig. 2 is a temperature profile, comprises Temperature Distribution, the distribution of (c) dielectric rod virtual temperature in Temperature Distribution, (b) compensating plate in (a) dielectric rod.

Embodiment

Below in conjunction with attached Fig. 1 and 2 embodiments of the present invention are further described.

Lens ring among Fig. 1 (6) is converted into annular beam with the transmitted light of LD (9) behind optical fiber (8) and telescope (7); Lens ring that can be by changing different focal or regulate it and the relative distance of telescope, compensating plate (4) is adjusted it and is mapped to spot size on the compensating plate;

Speculum (5) is faced the high-reflecting film (High-reflectanceCoating, HR Coating) of the single face plating of resonant cavity to laser beam, and the anti-reflection film (Anti-reflectanceCoating, AR Coating) that LD is sent light beam is all plated on the two sides;

Compensating plate material itself has high-absorbility (such as greater than 90%) to laser beam full impregnated mistake to the LD light beam; And face the anti-reflection film of the single face plating of resonant cavity, be close to the high-reflecting film of the one side plating of heat sink (3) laser beam to laser beam and LD light beam;

Modes such as heat sink employing liquid are cooled off the cryogenic temperature dynamic adjustable; And adopt modes such as pad indium (In) or heat conductive silica gel between the compensating plate so that heat conduction is good;

Outgoing mirror (1), working-laser material (2), speculum, compensating plate constitute the DPSSL of profile pump;

The LD light beam through optical fiber, telescope, lens ring and focusing mirror to the compensating plate surface.

Through analog computation as can be known, the Temperature Distribution in the laser medium barred body is shown in Fig. 2 (a), and the Temperature Distribution in the compensation lamellar body is shown in Fig. 2 (b), and the Temperature Distribution of equivalence is shown in Fig. 2 (c).As can be seen, Fig. 2 (c) is smoothly many more than Fig. 2 (a), and corresponding therewith, the variations in refractive index that is caused by temperature will reduce, and thermal lensing effect is compensated.Above-mentioned analog computation result is confirmed by experiment.

Claims (3)

1. the thermal effect compensation system of a laser is made of temperature-compensating medium, thermal source, cooling device, optical system, and wherein, the temperature-compensating medium is used for the hot distortion effect of dynamic compensation laser beam; Thermal source and cooling device are used to generate the required Temperature Distribution of temperature-compensating medium; Optical system is used for thermal source is focused on the temperature-compensating dielectric surface.

2. thermal effect compensation according to claim 1 system, used temperature-compensating material is an optical filter in the system, and the luminous wave band of laser working medium is seen through, the thermal source wave band used to bucking-out system absorbs.

3. but the laser of dynamic adjustments self Temperature Distribution, its resonant cavity comprises the described temperature compensation system of claim 1, and object such as laser working medium, chamber mirror.

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