CN2560132Y - Solid laser resonator - Google Patents

Abstract

The utility model relates to the manufacturing technology of a resonant cavity of a solid laser resonator, which comprises an end face mirror, a laser medium in the cavity, a folding mirror and an outputting mirror. Using the resonant cavity transforming circle theory, an M #-[1] mirror with short radius curvature is used for replacing an M #-[1] flat mirror of the general V-shaped cavity; a concave mirror with the corresponding rate radius is used for replacing the folding mirror and a flat reflecting mirror in the general V-shaped cavity, and the cavity structure is greatly simplified and shortened; frequency doubling crystals of KTP, etc. are arranged on an 'image' point from a thermal lens to the concave mirror to ensure the spot size of the frequency doubling crystals to have little influence with the change of the thermal lens size. A flat mirror is used as the folding outputting mirror between the laser medium and the frequency doubling crystals to high transmit for frequency doubling light, high reflect for base frequency light, prevent the green light from returning the laser medium, bring the laser medium to be additionally absorbed, and accelerate the heat effect. The utility model has the advantage of compact structure and compresses the laser volume, and no astigmatism element is arranged in the cavity, which ensures light beams to be provided with better quality and great economic benefits.

Description

A kind of resonant cavity of solid state laser

Affiliated technical field

The utility model is to belong to semiconductor laser diode pumping all-solid-state laser technical field, relates to the improvement of resonant cavity of solid state laser and laser diode-pumped solid state laser manufacturing technology.

Background technology

The microminiaturization of laser diode-pumped solid state laser is one of interest emphasis of people always.In recent years, the diode laser end-pumped solid-state laser is studied [L.Y.Liu, M.Oka, W.Wiechmann andKolota, Opt.Lett., 19,189 (1994) widely; W.A.Clarkson and D.C.Hanna, Opt.Lett., 21,737 (1996); W.A.Clarkson and D.C.Hanna, Opt.Lett., 21,869 (1996); M.Tsunekane, N.Taguchi and H.Inaba, Opt.Lett., 21,1912 (1996)].In the v-shaped cavity structure that adopts mostly in this laser shown in Fig. 1 (a).This cavity configuration is used to [H.Kogelnik, E.P.Ippen, A.Dienes and C.V.Shank, IEEE J.Quantum Electron., QE-8,373 (1972)] in the dye laser at first.In this v-shaped cavity structure, two end mirrors adopt plane mirror M ₁, M ₂, middle refrative mirror M is the concave mirror than short-radius.For avoiding the astigmatism function influence of refrative mirror, adopt usually to be less than 7 ° angle folding.Because refrative mirror is made high reflectivity mirror easily, is beneficial to reduce cavity loss; Use the refrative cavity structure, can shorten the length of laser to a certain extent.Simultaneously, be easy at the M that folds galianconism ₂Mirror one end produces little girdling the waist, and in order to placing frequency-doubling crystal herein, realizes frequency-doubled conversion effectively.This is the main cause that people are ready to adopt V-type.But mainly only considered the compensation problem of the astigmatism that refrative mirror wherein causes in the document, and do not considered the influence problem of the thermal lens that comprises in the chamber.But in solid state laser, thermal lensing effect is a significant effects factor.Pass through dynamic analysis [Song Feng, Zhang Guangyin, Xu Jingjun to the V-type Solid State Laser chamber that comprises thermal lens, Zhang Chaobo, Chin.Phys.Lett., 17,303 (2000)] have practical meaning, can design a kind of new laser cavity resonator structure.

Equivalent light path at v-shaped cavity shown in Fig. 1 (b).For analyzing for simplicity, ignored the effect of astigmatism here.Thereby the lens F of available single focal length value equivalence refrative mirror M, (majority is Nd:YAG or the Nd:YVO of thickness 1～8mm with laser medium ₄Wafer) equivalence is one and is close to level crossing M ₁Thin thermal lens F _t, its focal length value f _tWith the increase of optical pumping power, can be changed to tens centimetres from ∞.Thermodynamic parameter 1/f _tThe amplitude variation is an important feature in this V-type Solid State Laser chamber greatly.Its conversion circle diagram of optical mode characteristic shown in Figure 2 is separated analysis.Can derive at situation (1) f by conversion circle theory _t＞l ₁During-f (f is the focal length value of equivalent lens F herein), F-M ₂Side focal position in the arm of chamber is (at σ ₂On the circle) and parameter with a tight waist: $b_2=\frac{{\mathrm{<figure-callout\; id="2"\; label="f"\; filenames="Y0223834300102.png"\; state="\{\{state\}\}">f</figure-callout>}}_2}{2(l_1-f)}\sqrt{\frac{-{\mathrm{<figure-callout\; id="1"\; label="l"\; filenames="Y0223834300102.png,Y0223834300121.png"\; state="\{\{state\}\}">l</figure-callout>}}_1+f-f_t}{l_1-f-f_t}}---\left(1\right)$ ${\mathrm{<figure-callout\; id="2"\; label="w"\; filenames="Y0223834300102.png"\; state="\{\{state\}\}">w</figure-callout>}}_2=\sqrt{\frac{b_2\mathrm{\&lambda;}}{\mathrm{\&pi;}}}={\left[\frac{{\mathrm{<figure-callout\; id="2"\; label="f"\; filenames="Y0223834300102.png"\; state="\{\{state\}\}">f</figure-callout>}}^2\mathrm{\&lambda;}}{2\mathrm{\&pi;}(l_1-f)}\sqrt{\frac{{-\mathrm{<figure-callout\; id="1"\; label="l"\; filenames="Y0223834300102.png,Y0223834300121.png"\; state="\{\{state\}\}">l</figure-callout>}}_1+f-f_t}{l_1-f-f_t}}\right]}^{\frac{1}{2}}---\left(2\right)$ W shown in Fig. 3 ₂～1/f _tRelation curve.

As situation (2) f _t＞l ₁During-f, M ₂The basic mode spot size of ' Jing Chu is ${\mathrm{<figure-callout\; id="2"\; label="w"\; filenames="Y0223834300102.png"\; state="\{\{state\}\}">w</figure-callout>}}_2^{\&prime;}={\left[\frac{{\mathrm{<figure-callout\; id="2"\; label="f"\; filenames="Y0223834300102.png"\; state="\{\{state\}\}">f</figure-callout>}}^2\mathrm{\&lambda;}}{2\mathrm{\&pi;}(l_1-f)}\sqrt{\frac{{-\mathrm{<figure-callout\; id="1"\; label="l"\; filenames="Y0223834300102.png,Y0223834300121.png"\; state="\{\{state\}\}">l</figure-callout>}}_1+f+{3f}_t}{l_1-f-f_t}}\right]}^{\frac{1}{2}}---\left(3\right)$ W shown in Figure 3 ₂'～1/f _tRelation curve.Following formula only exists $\frac{l}{l_1-f}<\frac{1}{f_t}<\frac{3}{l_1-f}$ Shi Youshi separates.

At F _tIn the arm of-F chamber, M ₂The σ of mirror ₂Picture σ behind the flexible F lens transformation excessively ₂' circle also has two kinds of situations, can try to achieve F under the situation (1) equally _tThe basic mode light beam parameters and the F at place _tThe basic mode spot size at place: $b_t=\frac{(l_1-f)f_t}{\sqrt{f_t^2-{(l_1-f)}^2}}---\left(4\right)$ $w_t={\left[\frac{\mathrm{\&lambda;}(l_1-f)f_t}{\mathrm{\&pi;}\sqrt{f_t^2-{(l_1-f)}^2}}\right]}^{\frac{1}{2}}---\left(5\right)$ F under another kind of situation (2) _tThe basic mode spot size at place: $w_t^{\&prime;}={\left[\frac{\mathrm{\&lambda;}(l_1-f)f_t}{\mathrm{\&pi;}\sqrt{4(l_1-f)f_t-{(l_1-f)}^2-3f_t^2}}\right]}^{\frac{1}{2}}---\left(6\right)$ Fig. 4 illustrates w _t～1/f _tWith w _tThe relation curve of '～1/ft.As can be seen from the figure, in situation (1), laser cavity can only be in half pairing dynamical stability district of " U " deltoid, promptly $0<\frac{1}{f_t}<\frac{1}{l_1-f}$ In, stable operation; Under situation (2), laser cavity can be in the pairing dynamical stability of whole " U " deltoid district, promptly $\frac{1}{l_1-f}<\frac{1}{f_t}<\frac{3}{l_1-f}$ In, stable operation.This and w ₂, w ₂' to have the real dynamical stability district that separates be consistent (see figure 3).Therefore, in situation (2), than situation (1), the dynamical stability district that can have the reality of twice broad to move.But when actual motion, note working as 1/f _tBe worth approaching

The time, w ₂' become very little, make M ₂' mirror bears the laser action of bigger power density, causes M easily ₂The light injury of ' mirror.But because the aperture of the active region of laser medium is limited, this extreme that can limit the practical laser power density increases, and above-mentioned situation generally is avoidable.

The basic mode spot size at thermal lens place can be moved M by axle ₂The position of mirror and being adjusted.By the resonant cavity of situation (1) setting, if we are with M ₂Mirror moves to left to the right focus O ' of F lens and locates, at this moment, and σ ₂' circle is the straight line of left focus O by the F lens.In this case, w _tMinimum value will appear at $\frac{1}{f_t}=\frac{1}{2(l_1-f)}$ The place, its value is for afore-mentioned Doubly (seeing Fig. 5 (a)).

By the resonant cavity of situation (2) setting, if we are with M ₂Mirror further moves to right to M ₂" locate, from S ₁₁" distance be 2 Δs ⁺, at this moment, thermal lens F _tThe minimum basic mode spot size at place can also enlarge.In Fig. 5 (b), provide its graphic representation.At this moment, at thermal lens F _tThe minimum basic mode light beam parameters b at place " _MinBe M ₂' from S ₁₁" distance be Δ ⁺The time minimum basic mode light beam parameters b " _MinTwo times, also be that minimum basic mode spot size can enlarge again

Doubly.

In the above two kinds of cases, can correspondingly increase the cross section of the active region of end pumping illumination in laser medium, thereby thermal lensing effect is correspondingly weakened.

Resonant cavity by situation (2) configuration though above-mentioned advantage is arranged, has its shortcoming.This mainly is that it has to operate at $\frac{1}{f_t}>\frac{1}{l_1-f}$ Dynamic regime.At this moment, the optical pumping input power is bigger, causes tangible thermal stress and double focusing effect easily in laser medium, and relevant optical loss, and the efficient of laser is reduced.

From the dynamic analysis of top optical mode characteristic to general-purpose V-type Solid State Laser chamber as can be seen, the basic mode spot size w at laser bar place _t(see figure 4) or M ₂The basic mode spot size w of Jing Chu ₂(see figure 3) exists $\frac{1}{f_t}\&ap;\frac{1}{l_1-f}$ Near all be tending towards the ∞ value, cause chamber mould running wastage to heighten, and laser can't be moved.This is the fatal shortcoming in general-purpose V-type Solid State Laser chamber.

Recently, people such as Liu Jun-hai has proposed improved v-shaped cavity structure.In resonant cavity, if be R with a radius of curvature by situation (2) configuration ₁The concave mirror of=15cm replaces level crossing M ₁, promptly approximate with the resonant cavity of work in [Liu J H, Wang C Q, L ü J H, Li G M, Shao Z S, Wang J Y, Liu Y G, Jiang M H 1999 Chin.Phys.Lett.16 508].In the v-shaped cavity after so improving, the dynamical stability district can be moved to low value 1/f _tDynamic regime.Therefore, when extremely low optical pumping power input, can make laser cavity stable operation; Simultaneously, because the cavity loss that this moment, thermal stress caused can be ignored, the operational efficiency of laser is higher.

Summary of the invention

The purpose of this utility model is to provide a kind of resonant cavity of solid state laser, removes folding concave mirror and speculum in the v-shaped cavity on the above-mentioned improved basis, the substitute is the concave output mirror of corresponding radius of curvature, simplifies and shortened cavity configuration greatly.The utility model compact conformation has greatly compressed the laser volume, and no astigmatism element in the chamber can guarantee that light beam has better quality.

The utility model comprises that V-type resonant cavity, laser medium, refrative mirror, outgoing mirror and end mirror constitute, and it is characterized in that: described end mirror is concave mirror M ₁, described outgoing mirror is concave mirror M ₂', also comprise flat-folded mirror M ₃, constitute resonant cavity of solid state laser.

Described outgoing mirror is high anti-to fundamental frequency light under the frequency multiplication situation; Described outgoing mirror M ₂' and refrative mirror M ₃Between place frequency-doubling crystal; Described refrative mirror M ₃High saturating to frequency doubled light, high anti-to fundamental frequency light.

Described frequency-doubling crystal places thermal lens to described concave mirror M ₂' ' as ' on the point; Described frequency-doubling crystal is a ktp crystal.

Described fundamental frequency light outgoing mirror (under the frequency multiplication situation, high anti-) M to fundamental frequency light and frequency doubled light ₂', M ₂' radius of curvature and the design of the position of placement can calculate according to resonant cavity conversion circle theoretical formula, Calculation Method is the theoretical formula with the thermal focal length parameter substitution resonant cavity conversion circle of the position of the position of long, the folding concave mirror of laser chamber, KTP frequency-doubling crystal and laser crystal, can obtain the conversion circle σ of flat output mirror by folding concave mirror ₂' circle, M at this moment ₂' radius of curvature equal σ ₂' diameter of a circle, the position is corresponding to σ ₂The right intersection point place of ' circle and optical axis.

Described under the frequency multiplication situation, frequency-doubling crystal KTP is placed thermal lens F _tTo mirror M ₂' ' as ' point on, ' as ' position of point can try to achieve by resonant cavity conversion circle theoretical formula.

Other frequency-doubling crystals such as the also available LBO of the utility model, KDP place on thermal lens ' as ' point to outgoing mirror, can make the spot size at frequency-doubling crystal place not be subjected to the considerable influence of thermal lens size variation.Do refrative mirror with a level crossing between laser medium and frequency-doubling crystal, this mirror is high saturating to frequency doubled light (532nm), and is high anti-to fundamental frequency light (1.064 μ m), can prevent green glow return laser light medium, causes the laser medium additional absorption, the aggravation thermal effect.

The utility model compact conformation has greatly compressed the laser volume, and no astigmatism element in the chamber can guarantee that light beam has better quality, and have great economic benefit.

Description of drawings

Fig. 1 general-purpose V-type Solid State Laser cavity configuration figure (a) and equivalent light path (b) thereof; Conversion graphical analysis (a) situation (1) in Fig. 2 general-purpose V-type chamber, (b) situation (2); W in Fig. 3 general-purpose V-type chamber ₂-1/f _tWith w ₂'-1/f _tRelation curve, when calculating, get l ₁=250mm, f=50mm, λ=1.06 μ m.; W in Fig. 4 general-purpose V-type chamber _t-1/f _tWith w _t'-1/f _tRelation curve, when calculating, get l ₁=250mm, f=50mm, λ=1.06 μ m.; M in Fig. 5 general-purpose V-type chamber ₂Mirror move to (a) O ' locate with (b) from S ₁₁" distance be 2 Δs ⁺Thermal lens F during the place _tLocate the diagram of minimum basic mode spot size situation of change; Fig. 6 has proposed a kind of equivalent structure figure of improved v-shaped cavity structure for people such as Liu Jun-hai; Fig. 7 is the w of Fig. 6 cavity configuration _t'-1/f _tRelation curve; Fig. 8 is an equivalent cavity structure of the present utility model.

Embodiment

Fig. 8 is an equivalent cavity structure of the present utility model.

Getting l ₁=250mm, f=50mm, R ₁=150mm.Here have only " U " curve, another drops on 1/f _t→ ∞ place.1/f _t=0 ordinate and this " U " curve intersection.1/f _t" U " curve of＞0 just is of practical significance.At this moment, σ ₁' diameter of a circle $R_{}^{}$ ${}_1^{\&prime;}=\frac{f_t{R}_1}{f_t+{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="Y0223834300102.png,Y0223834300121.png"\; state="\{\{state\}\}">R</figure-callout>}}_1},$ Thermal lens F _tThe basic mode light beam parameters at place is $b^{\&prime;}=\frac{(l_1-f){\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="Y0223834300102.png,Y0223834300121.png"\; state="\{\{state\}\}">R</figure-callout>}}_1^{\&prime;}}{\sqrt{4(l_1-f){\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="Y0223834300102.png,Y0223834300121.png"\; state="\{\{state\}\}">R</figure-callout>}}_1^{\&prime;}-{(l_1-f)}^2-3{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="Y0223834300102.png,Y0223834300121.png"\; state="\{\{state\}\}">R</figure-callout>}}_1^{\&prime;2}}}$ Thermal lens F _tThe basic mode spot size at place $w_t^{\&prime;}=\sqrt{\frac{b^{\&prime;}\mathrm{\&lambda;}}{\mathrm{\&pi;}}}.$ When ${\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="Y0223834300102.png,Y0223834300121.png"\; state="\{\{state\}\}">R</figure-callout>}}_1^{\&prime;}=\frac{1}{2}(l_1-f)$ The time, b ' has a minimum value: b ' _Min=l ₁-f correspondingly, has minimum basic mode spot size $w_{\min }^{\&prime;}=\sqrt{\frac{(l_1-f)\mathrm{\&lambda;}}{\mathrm{\&pi;}}}.$ As at document [Zhang G Y, Song F, Feng Y, Xu J J 2000 Acta phys.Sina.491495 (in Chinese) [Zhang Guangyin, Song Feng, Feng Yan, Xu Jing army 2000 Acta Physica Sinicas 49 1495]] in pointed out, the aperture of active region can be extended to 1.2 times of minimum basic mode limiting aperture, all can guarantee basic mode operation in the whole effective power stable region under the restriction in this aperture.At this moment, minimum basic mode light beam parameters b ' in the basic mode light beam parameters of the boundary of effective power stable region operation is distinguished for this _Min1.44 times, b '=1.44 (l are promptly arranged ₁-f), so can get R ₁' two separate into ${\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="Y0223834300102.png,Y0223834300121.png"\; state="\{\{state\}\}">R</figure-callout>}}_{1\&PlusMinus;}^{\&prime;}=\frac{(5.76\&PlusMinus;2.07)(l_1-f)}{10.03}.$ And by l ₁=250mm, f=50mm then has l ₁-f=200mm is so can try to achieve: R ₁₊'=156mm; R _1-'=73.6mm.Here, if adopt concave mirror M ₁Radius of curvature is R ₁=150mm.So, work as f _tWhen ∞ is changed to 150mm, σ ₁' diameter of a circle R ₁' be 75mm.By R ₁The σ that determines ₁The circle and by R ₁' definite σ ₁' circle all drops on by R ₁₊' definite σ ₁₊' circle and by R _1-' definite σ _1-Between ' the circle; And σ ₁Circle next-door neighbour σ ₁₊' circle, σ ₁' circle next-door neighbour σ _1-' circle.This means, at f _tUnder the situation of the big amplitude variation of ∞ to 150mm, portion can satisfy the requirement of basic mode stable operation.Work [Liu J H, Wang C Q, L ü J H, LiGM, Shao Z S, Wang JY, Liu Y G, Jiang M H 1999 Chin.Phys.Lett.16 508] in the cavity resonator structure that adopts and parameter thereof and above-mentioned analysis adopt very close, the result of their experimental result and above-mentioned analysis is also close completely.This shows that above-mentioned analysis is believable.

Above-mentioned v-shaped cavity is used as the inner cavity frequency-doubling laser cavity.Only need frequency-doubling crystals such as KTP or LBO (4～5mm is thick) are positioned over next-door neighbour M in the chamber ₂Mirror one end.Because M ₂The basic mode spot size w with a tight waist of Jing Chu ₂Or w ₂' less (see figure 3), this helps the conversion of fundamental frequency light to frequency doubled light.But also should see w ₂Or w ₂' with 1/f _tVariation comparatively obvious; Particularly, w ₂' with 1/f _tWhen big value changes, the trend of trend zero is arranged, at this moment, be easy to cause the light injury of frequency-doubling crystal.If frequency-doubling crystal is left M slightly ₂Mirror promptly places thermal lens F _tOn the picture point to lens F, at f _tUnder the situation that big amplitude changes, the basic mode spot size at frequency-doubling crystal place can remain unchanged basically.This can be avoided because f _tBig amplitude change the chamber inner light beam that may cause on frequency-doubling crystal focusing and the light injury that causes.This v-shaped cavity shown in Figure 1 just should be noted that in use and prevents.Must point out that also this cavity configuration meets the requirement that two heat are disturbed the thermal insensitive cavity under the situation of center just.

Claims (5)

1, a kind of resonant cavity of solid state laser, described resonant cavity comprise that V-type resonant cavity, laser medium, refrative mirror, outgoing mirror and end mirror constitute, and it is characterized in that: described end mirror is concave mirror M ₁, described outgoing mirror is concave mirror M ₂', also comprise flat-folded mirror M ₃, constitute resonant cavity of solid state laser.

2, resonant cavity of solid state laser according to claim 1 is characterized in that described outgoing mirror M ₂' and refrative mirror M ₃Between place frequency-doubling crystal.

3, resonant cavity of solid state laser according to claim 2 is characterized in that described refrative mirror M ₃High saturating to frequency doubled light, high anti-to fundamental frequency light.

4, resonant cavity of solid state laser according to claim 2 is characterized in that described frequency-doubling crystal places thermal lens to described concave mirror M ₂' ' as ' on the point.

5, resonant cavity of solid state laser according to claim 1 is characterized in that described frequency-doubling crystal is a ktp crystal.

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