CN117650414A - Optical parametric oscillator with partially unstable cavity structure and method - Google Patents
Optical parametric oscillator with partially unstable cavity structure and method Download PDFInfo
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Abstract
The invention belongs to the technical field of unstable cavity lasers, and particularly discloses an optical parametric oscillator with a partial unstable cavity structure and a construction method thereof. The optical fiber comprises a first cavity mirror, a first cylindrical mirror, a thin strip nonlinear optical crystal, a second cylindrical mirror and a second cavity mirror which are sequentially arranged along an optical path; the first cavity mirror and the second cavity mirror are plane mirrors. The invention is based on the partial unstable cavity technology, and creatively provides the thought of adding the partial unstable cavity structure aiming at the problems of low conversion efficiency, poor beam quality and the like of the double-pass pump optical parametric oscillator, adopts the thin plate strip nonlinear optical crystal, the cylindrical mirror I and the cylindrical mirror II to form the partial unstable cavity, utilizes the multi-pass reflection folded optical path to improve the optical path, the thermal lens effect of the nonlinear optical crystal and the mode limiting effect of the partial unstable cavity in the horizontal and vertical directions, realizes the double-pass pump optical parametric oscillator with high efficiency and high beam quality, and expands the application scene of the optical parametric oscillator with the partial unstable cavity structure.
Description
Technical Field
The invention belongs to the technical field of unstable cavity lasers, and particularly relates to an optical parametric oscillator with a partial unstable cavity structure and a method thereof.
Background
Along with the development of science and technology and the increase of economy, the laser technology is widely applied to the fields of industry, scientific research, biology, medical treatment and the like, the laser wave band expansion is realized based on the nonlinear frequency conversion technology, and the wavelength is tunable, the conversion efficiency is high, and the high-beam quality output becomes a research hot spot. In nonlinear frequency conversion, as the resonant cavity of the optical parametric oscillator is shorter, the acting length of the injected pump light in the resonant cavity is shorter, the conversion efficiency is limited, and meanwhile, the shorter resonant cavity length is also unfavorable for the suppression of the resonant cavity on the high-order transverse mode; the nonlinear crystal has certain absorption to parametric light (pumping, signals and idler frequencies), so that a thermal lens effect exists, the utilization rate of the pumping light is low, and the quality of the light beam is seriously degraded. In order to obtain higher conversion efficiency, the pump light needs to be focused and injected into the optical parametric oscillator, and the pump light rapidly diverges after being focused, so that higher requirements are also put forward on the control of the beam quality.
Currently, the beam quality can be described using the pulse pump single resonance threshold and Shan Gongzhen optical parametric oscillator conversion efficiency:
1. the single resonance threshold is pulsed. Currently, most of the operation of optical parametric oscillators is performed under the pumping of pulsed light, because pulsed pump light has a sufficiently high peak power density to easily reach the threshold required for successful operation of the optical parametric oscillator. While theoretical derivation of this threshold has been done by bayer and Brosman et al as early as 1979, which consider the walk-off effect, a gaussian distribution simplification was applied to both the temporal and spatial distribution of the pump light, resulting in an analytical expression of the threshold pump energy flux for single resonance under single-pass pulsed pumping conditions:
wherein F is th For threshold pump flux, the unit is J/cm 2 The method comprises the steps of carrying out a first treatment on the surface of the τ is the pump pulse width; c is the speed of light in vacuum; l is the physical length of the crystal; l is the optical length of the resonant cavity; alpha is the absorption coefficient of the signal light in the crystal; r is the reflectivity of the resonant cavity output mirror to the signal wavelength;
ζ is the effective parametric gain length, expressed as:
wherein l w The walk-off length can be written as:
in formula (3), w p And w s Spot radii of the pump light and the signal light, respectively, are generally w p ＝w s The method comprises the steps of carrying out a first treatment on the surface of the ρ is the walk-off angle; k and g s Respectively nonlinear coupling constants and signal light mode coupling constants, and their expressions are as follows:
in the formulas (4) - (5), ε 0 Is vacuum dielectric constant;
d eff is the effective nonlinear coefficient of the nonlinear crystal; lambda (lambda) s And lambda (lambda) i Signal light wavelength and idler light wavelength respectively; n is n p 、n s And n i Refractive indexes of pump light, signal light and idler light in the nonlinear crystal respectively;
2. shan Gongzhen optical parametric oscillator conversion efficiency. For the convenience of theoretical calculation, it is assumed that three wavelengths involved in nonlinear conversion realize accurate phase matching, and under the assumption, a conversion efficiency expression of the single-resonance optical parametric oscillator can be obtained:
in equation (6), f (x) is solved by the following equation:
based on the above-mentioned drawbacks and shortcomings, there is a need in the art to propose an optical parametric oscillator with a partially unstable cavity structure, so as to solve the problems of low pump light utilization rate and serious degradation of beam quality in the prior art.
Disclosure of Invention
Aiming at the defects or improvement demands of the prior art, the invention provides a partial unstable cavity structure optical parametric oscillator and a method thereof, wherein partial unstable cavities are introduced into the optical parametric oscillator, the thermal lens effect of nonlinear optical crystals and the mode limiting effect of partial unstable cavities in the horizontal and vertical directions are utilized, the optical parametric oscillator has an important effect on improving the beam quality of output signal light, and the multi-pass amplification increases the nonlinear acting distance and is beneficial to improving the conversion efficiency.
In order to achieve the above object, according to one aspect of the present invention, there is provided a partially unstable cavity optical parametric oscillator comprising a first cavity mirror, a first cylindrical mirror, a thin plate strip nonlinear optical crystal, a second cylindrical mirror and a second cavity mirror sequentially arranged along an optical path, wherein,
the pump light is injected into the optical parametric oscillator through the cavity mirror I, the pump light passes through the thin plate strip nonlinear optical crystal in the process of being reflected by the cylindrical mirror I and the cylindrical mirror II for multiple times, in the process, the pump light generates signal light and idler frequency light, the idler frequency light is projected out of the cavity by plating the coating design idler frequency light on the surfaces of the cylindrical mirror I, the cylindrical mirror II, the cavity mirror I and the cavity mirror II, the residual light spots of the pump light and the signal light are amplified according to the geometric amplification rate M in the horizontal direction, the size of the light spots is kept unchanged in the vertical direction, the reflected pump light and the amplified signal light are reflected by the cavity mirror II and returned along an original light path, the cavity mirror II is highly reflected by the pump light, the coupling output rate T is achieved after the reflected pump light and the signal light pass through the thin plate strip nonlinear optical crystal between the cylindrical mirror II and the cylindrical mirror I for multiple times, the light spots of the pump light and the signal light are reduced according to the geometric reduction rate 1/M in the horizontal direction, the light spots of the residual pump light and the signal light are not limited in the vertical direction, the light spots are not limited by the size of the cavity mirror I and the cavity II, the resonant light is high in the cavity and the quality is increased, and the quality of the cavity is increased between the cavity I and the cavity resonator light is increased, and the cavity light is high.
As a further preferred aspect, the slab nonlinear optical crystal has a size satisfying: the length is more than or equal to the width and is thicker than the thickness;
and the long x wide face of the slab nonlinear optical crystal is used as a horizontal plane.
As a further preferred aspect, the slab nonlinear optical crystal is KTP crystal or KTA crystal having non-critical phase matching.
As a further preferable mode, the first cylindrical mirror is a plano-concave cylindrical mirror, the bus of which is perpendicular to the horizontal plane, and the second cylindrical mirror is a plano-convex cylindrical mirror, and the bus of which is perpendicular to the horizontal plane.
As a further preferable mode, the curvatures of the first cylindrical mirror and the second cylindrical mirror are respectively R1 and R2, and the distances between the first cylindrical mirror and the second cylindrical mirror are respectively (R1+R2)/2.
As a further preferred aspect, the geometrical magnification of the beam by the unstable cavity formed by the first and second cylindrical mirrors is m= |r1/r2| in the horizontal direction, and the flat critical cavity formed by the first and second cylindrical mirrors in the vertical plane direction forms a stable cavity in the presence of the thermal focal length of the slab nonlinear optical crystal to confine the pump light and the signal light and idler light generated by nonlinear conversion to the thickness direction of the slab nonlinear optical crystal.
As a further preferable aspect, the geometric magnification M is 1.1 to 1.3 to limit the beam divergence of the pump light and the signal light in the horizontal direction.
According to another aspect of the present invention, there is also provided a method for outputting laser light by a partially unstable cavity structure optical parametric oscillator, comprising the steps of:
step one, building an optical path system: in the horizontal direction, a first cavity mirror, a first cylindrical mirror, a thin strip-shaped nonlinear optical crystal, a second cylindrical mirror and a second cavity mirror are sequentially arranged along an optical path, wherein the thin strip-shaped nonlinear optical crystal is arranged between the first cylindrical mirror and the second cylindrical mirror;
and secondly, pumping light is injected into an optical parametric oscillator through a cavity mirror I, the pumping light passes through the thin plate strip-shaped nonlinear optical crystal in the process of being reflected by the cylindrical mirror I and the cylindrical mirror II for multiple times, in the process, the pumping light generates signal light and idler frequency light, the idler frequency light is cast out of the cavity by plating the coating design idler frequency light on the surfaces of the cylindrical mirror I, the cylindrical mirror II, the cavity mirror I and the cavity mirror II, the idle frequency light is lost, the light spots of the rest pumping light and the signal light are amplified in the horizontal direction according to the geometric amplification rate M, the light spots are limited in the vertical direction and are kept unchanged by the stable cavity light spot size, the reflected pumping light and amplified signal light returns along an original light path by the cavity mirror II, the cavity mirror II is highly reflected by the pumping light, the coupling output rate is T, the reflected pumping light and signal light pass through the thin plate strip-shaped nonlinear optical crystal between the cylindrical mirror II and the cavity mirror I for multiple times, the light spots of the pumping light and the signal light are reduced in the horizontal direction according to the geometric reduction rate 1/M, the light spots of the laser beam is not limited in the vertical direction and the stable cavity size is not limited by the cavity mirror I, the resonant cavity is high, the quality is enhanced by the resonant cavity is enhanced, and the quality is increased by the cavity I and the resonant cavity is high, and the resonant cavity is formed by the resonant cavity is high.
As a further preferable aspect, in the second step, the geometric magnification M is 1.1 to 1.3 to limit the beam divergence of the pump light and the signal light in the horizontal direction.
In general, compared with the prior art, the above technical solution conceived by the present invention mainly has the following technical advantages:
1. the invention improves the beam quality of the laser output by the optical parametric oscillator by utilizing the strong constraint capability of part of unstable cavity light spots. Meanwhile, part of the unstable cavity can realize multi-path folded light path transmission, the nonlinear acting distance is increased, and the nonlinear conversion efficiency can be improved.
2. The invention adds partial unstable cavity structure in the original optical parametric oscillator to increase the restraint of the light beam in the horizontal and vertical directions, thereby being beneficial to the improvement of the light beam quality.
3. In the unstable cavity structure, the effective acting distance of the light beam is increased by repeatedly reciprocating the light beam, so that the conversion efficiency is improved.
4. The pump light is injected into an optical parametric oscillator through a cavity mirror I, the pump light passes through the thin plate strip nonlinear optical crystal in the process of being reflected by the cylindrical mirror I and the cylindrical mirror II for multiple times, in the process, the pump light generates signal light and idler frequency light, the idler frequency is projected out of a cavity by plating the coating design idler frequency light on the surfaces of the cylindrical mirror I, the cylindrical mirror II, the cavity mirror I and the cavity mirror II, the idle frequency light is lost, the light spots of the rest pump light and the signal light are amplified in the horizontal direction according to the geometric amplification rate M, the light spots are limited in the vertical direction and kept unchanged by the stable cavity light spot size, the reflected pump light and the amplified signal light are reflected by the cavity mirror II and returned along an original light path, the cavity mirror II is highly reflected by the pump light, the coupling output rate is T, the reflected pump light and the signal light pass through the thin plate strip nonlinear optical crystal between the cylindrical mirror II and the cylindrical mirror I for multiple times, the light spots of the pump light and the signal light are reduced in the horizontal direction according to the geometric reduction rate 1/M, the light spots of the laser light is not limited in the vertical direction and the cavity size is not limited by the cavity mirror I and the cavity light spot size, the resonant light is high in the cavity and the cavity is high in quality, and the cavity quality is enhanced.
5. The invention specifically designs the geometric magnification of the partial unstable cavity mirror, and ensures the stability and the beam quality of the pumping light spot in the process of multiple reflection.
Drawings
FIG. 1 is a schematic diagram of a partially unstable cavity optical parametric oscillator in a horizontal direction according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a partially unstable cavity optical parametric oscillator in a vertical direction according to an embodiment of the present invention;
fig. 3 is a schematic diagram showing the threshold power and the conversion efficiency of a partially unstable resonator optical parametric oscillator in a single resonance mode in embodiment 2 of the present invention.
Like reference numerals denote like technical features throughout the drawings, in particular: 1-cavity mirror I, 2-cylindrical mirror I, 3-thin strip nonlinear optical crystal, 4-cylindrical mirror II, 5-cavity mirror II, 6-pump light, 7-signal light and 8-idler light.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention. In addition, the technical features of the embodiments of the present invention described below may be combined with each other as long as they do not collide with each other.
As shown in fig. 1, the optical parametric oscillator with a partially unstable cavity structure provided by the embodiment of the invention comprises a first cavity mirror 1, a first cylindrical mirror 2, a strip-shaped nonlinear optical crystal 3, a second cylindrical mirror 4 and a second cavity mirror 5 which are sequentially arranged along an optical path. The pump light 6 is injected into the optical parametric oscillator through the first cavity mirror 1;
the thin strip nonlinear optical crystal 3 is arranged between the cylindrical mirror 1 and the cylindrical mirror 4, the pump light 6 is injected and passes through the thin strip nonlinear optical crystal 3 in the process of being reflected by the cylindrical mirror 2 and the cylindrical mirror 4 for multiple times, in the process, the pump light 6 generates signal light 7 and idler light 8, the idler light 8 is projected and lost outside the cavity by coating the surfaces of the cylindrical mirror 2, the cylindrical mirror 4, the cavity 1 and the cavity 5 by the idler light 8, the spots of the residual pump light 6 and the signal light 7 are amplified in the horizontal direction according to the geometric magnification M, the size of the stable cavity spot is kept unchanged in the vertical direction, the reflected pump light 6 and the amplified signal light 7 are reflected by the cavity mirror 5 and returned along an original light path, the cavity mirror 5 is high in reflection, the signal light 7 is partially output, the coupling output rate T is achieved, the reflected pump light 6 and the signal light 7 pass through the thin strip nonlinear optical crystal 3 between the cylindrical mirror 4 and the first mirror 2, the spot size of the laser light 6 is reduced in the horizontal direction and the cavity 1 is not changed in the horizontal direction, the laser light 7 is reduced in the horizontal direction, the laser light spot size of the cavity 1 is reduced in the horizontal direction, and the laser light 7 is not reduced in the horizontal direction, and the laser light spot size of the cavity 1 is reduced, and the laser light 7 is reflected in the horizontal direction is reflected, the laser light 7 is reflected by the original light 7, and is reflected by the laser light 7, and is reflected, in the light is reflected, and in the signal light, and is reflected, and is.
More specifically, in an alternative embodiment of the present invention, as shown in fig. 1, in the horizontal direction, i.e., in the X-O-Y plane of the drawing, the pump light 6 is input to the first cavity mirror 1, then is input to the thin plate strip nonlinear optical crystal 3 through the first cavity mirror 1, is input to the first cylindrical mirror 2 through the thin plate strip nonlinear optical crystal 3, then is reflected to the thin plate strip nonlinear optical crystal 3, and then is input to the second cylindrical mirror 4 through the thin plate strip nonlinear optical crystal 3, i.e., the pump light 6 is reflected between the first cylindrical mirror 2 and the second cylindrical mirror 4 for multiple times through the thin plate strip nonlinear optical crystal 3 after passing through the thin plate strip nonlinear optical crystal 3.
More specifically, in an alternative embodiment of the present invention, as shown in fig. 1 and 2, the dimensions of the thin plate strip nonlinear optical crystal satisfy: the length is more than or equal to the width and is thicker than the thickness; and the long multiplied by the wide surface of the thin strip nonlinear optical crystal is used as a horizontal plane, and the thickness direction of the thin strip nonlinear optical crystal is a straight surface or a light passing surface. I.e. long along the X-axis and wide along the Z-axis. In the horizontal plane, the thin plate strip nonlinear optical crystal is arranged between the cylindrical mirror I2 and the cylindrical mirror II 4, and the cylindrical mirror I2 and the cylindrical mirror II 4 are staggered along the X direction, so that the pump light 6 passes through the thin plate strip nonlinear optical crystal and then is reflected between the cylindrical mirror I2 and the cylindrical mirror II 4 for multiple times to pass through the thin plate strip nonlinear optical crystal.
More specifically, in an alternative embodiment of the present invention, the thin plate strip nonlinear optical crystal is a KTP crystal or a KTA crystal with non-critical phase matching, that is, but not limited to, a KTP crystal, a KTA crystal with non-critical phase matching, and the like.
In order to achieve multiple reflections of pump light 6 between the first 2 and second 4 cylindrical mirrors, in an alternative embodiment of the invention, it may be, but is not limited to, plano-convex, plano-concave, plane mirrors, etc. More specifically, in an alternative embodiment of the present invention, the first cylindrical mirror 2 is a plano-concave cylindrical mirror with its generatrix perpendicular to the horizontal plane, and the second cavity mirror is a plano-convex cylindrical mirror with its generatrix perpendicular to the horizontal plane. The curvature of the first cylindrical mirror 2 is R1 (positive number), the curvature of the second cavity mirror 3 is R2 (negative number), and the distance between the first cylindrical mirror 2 and the second cylindrical mirror 4 is (R1+R2)/2.
In the invention, after the pump light 6 passes through the strip nonlinear optical crystal 1, the pump light passes through the thin plate strip nonlinear optical crystal 3 through multiple reflections between the cylindrical mirror I2 and the cylindrical mirror II 4, and in the process, the cylindrical mirror I2 and the cylindrical mirror II 4 are respectively positioned at two sides of the strip nonlinear optical crystal to form partial unstable cavities. In the horizontal direction, the geometric magnification of the unstable cavity formed by the cylindrical mirror I2 and the cylindrical mirror II 4 to the light beam is M= |R1/R2|, in the vertical plane direction, the flat critical cavity formed by the cylindrical mirror I2 and the cylindrical mirror II 4 forms a stable cavity under the condition that the thermal focal length of the thin plate strip nonlinear optical crystal 3 exists, so that the pumping light 6, the signal light 7 and the idler light 8 generated by nonlinear transformation are limited in the thickness direction of the thin plate strip nonlinear optical crystal 3.
More specifically, in the invention, the first cavity mirror 1 is a circular plane mirror, and has high transmission to the pump light 6 and the idler light 8 and high reflection to the signal light 7; the second cavity mirror 5 is a circular plane mirror and is highly reflective to the pump light 6. The pump light 6 is injected into the optical parametric oscillator through the first cavity mirror 1, and the thin strip nonlinear optical crystal 3, the first cylindrical mirror 2 and the second cylindrical mirror 4 form a part of unstable cavity structure with the geometric magnification of M in the horizontal direction and the stable cavity in the vertical direction; the injected pump light 6 passes through the thin plate strip nonlinear optical crystal 3 through multiple reflections between the cylindrical mirror I2 and the cylindrical mirror II 4, the horizontal direction of the light spot of the pump light 6 is amplified according to the geometric magnification M, the size of the light spot of the stable cavity is unchanged in the vertical direction, then the pump light 6 is reflected by the cavity mirror II 5 to return along the original light path, after the pump light passes through the thin plate strip nonlinear optical crystal 3 through multiple reflections between the cylindrical mirror I2 and the cylindrical mirror II 4, the horizontal direction of the light spot of the pump light 6 is reduced according to the geometric reduction 1/M, the size of the light spot of the stable cavity is unchanged in the vertical direction, and the pump light is output through the cavity mirror I1; because the thermal lens effect exists in the vertical plane of the thin strip nonlinear optical crystal 3, a stable cavity is formed in the vertical plane by the cavity structure formed by the thin strip nonlinear optical crystal 3, the cylindrical mirror I2 and the cylindrical mirror II 4, and the pump light 6 and the signal light 7 are restrained in the vertical direction; in the horizontal direction, the geometric magnification M of the cylindrical mirror I2 and the cylindrical mirror II 4 in the horizontal direction constrains the pump light 6 and the signal light 7, which is beneficial to improving the quality of the light beam; the signal light 7 is generated in the process that the pump light 6 passes through the thin plate strip nonlinear optical crystal 3 for many times, and is subjected to resonance enhancement in a resonant cavity formed by the first cavity mirror 1 and the second cavity mirror 5, so that high-efficiency high-beam quality output is realized.
In an alternative embodiment of the invention, the cylindrical mirror one 2, the cylindrical mirror two 4, the cavity mirror one 1 and the cavity mirror two 5 are all coated with a layer that is highly transparent to the idler light 8, in such a way that the idler light 8 will be lost out of the cavity after the concomitant generation of the signal light 7.
In addition, in order to limit the beam divergence degree of the pump light, the signal light, and the like in the horizontal direction, the value of the geometric magnification M is between 1.1 and 1.3.
In addition, based on any embodiment or a combination of embodiments, according to another aspect of the present invention, there is further provided a method for outputting laser light by a partially unstable cavity optical parametric oscillator, including the steps of:
step one, building an optical path system: in the horizontal direction, a first cavity mirror 1, a first cylindrical mirror 2, a thin plate strip nonlinear optical crystal 3, a second cylindrical mirror 4 and a second cavity mirror 5 are sequentially arranged along an optical path, wherein the thin plate strip nonlinear optical crystal 3 is arranged between the first cylindrical mirror 2 and the second cylindrical mirror 4;
and secondly, injecting the pump light 6 into the optical parametric oscillator through the cavity mirror 1, wherein the pump light 6 passes through the thin plate strip nonlinear optical crystal 3 in the process of being reflected by the cylindrical mirror 2 and the cylindrical mirror 4 for multiple times, in the process, the pump light 6 generates signal light 7 and idler light 8, coating films plated on the surfaces of the cylindrical mirror 2, the cylindrical mirror 4, the cavity mirror 1 and the cavity mirror 5 are designed to enable the idler light 8 to be projected out of the cavity to be lost, the light spots of the residual pump light 6 and signal light 7 are amplified in the horizontal direction according to the geometric amplification rate M, the reflected pump light 6 and amplified signal light 7 are reflected by the cavity mirror 5 to return along an original light path, the cavity mirror 5 is highly inverted to the pump light 6, the coupling output rate T is the coupling output rate T of the signal light 7, the reflected pump light 6 and the signal light 7 passes through the thin plate nonlinear optical crystal 3 for multiple times between the cylindrical mirror 4 and the cavity mirror 2, the light spots of the residual pump light 6 and the signal light 7 are amplified in the horizontal direction according to the geometric amplification rate M, the light spots of the cavity mirror 1 is reduced in the horizontal direction, the light spots of the cavity 6 and the cavity 7 are reduced in the horizontal direction, the light spots of the cavity is reduced in the horizontal direction of the cavity mirror 1 is not limited, the light spots of the cavity is reduced in the vertical direction of the cavity is reduced, and the cavity light spots of the laser light 7 is reduced in the horizontal direction of the cavity 1 is reduced, and the light spots of the laser light 7 is reflected in the cavity light 7 is reflected in the original light is reflected in the light beam is reflected in the cavity light beam is reflected by the cavity light beam 7, and is output.
In the method, a non-critical phase matching mode is adopted for the thin plate strip nonlinear optical crystal; the length, width and thickness of the strip nonlinear crystal are set to be equal to or larger than the width>The long-by-wide surface of the thin plate strip nonlinear optical crystal is a horizontal surface which is used as a large surface for uniform heat dissipation, the wide-by-thick surface of the thin plate strip nonlinear optical crystal is a vertical surface or a light-passing surface, and a film layer with high transmission of pump light, signal light and idler light is plated on the light-passing surface; the first cavity mirror and the second cavity mirror are respectively positioned at two sides of the lath nonlinear optical crystal to form a part of unstable cavity; the first cavity mirror and the second cavity mirror are respectively a plano-concave cylindrical mirror and a plano-convex cylindrical mirror, the bus is vertical to the horizontal plane, the curvatures are respectively R1 (positive) and R2 (negative), and the distance between the first cylindrical mirror 2 and the second cylindrical mirror 4 is (R1+R2)/2; in the horizontal plane direction, the geometric magnification M= |R1/R2| of the light beam, in the vertical plane direction, the cylindrical mirror I2 and the cylindrical mirror II 4 form a flat critical cavity, and the thermal focal length f exists in the thin plate strip nonlinear optical crystal th The stable cavity is formed under the condition that the pump light, the signal light and the idler frequency light generated by nonlinear transformation can be limited in the thickness direction of the thin-plate strip nonlinear optical crystal, so that the improvement of the light beam quality is facilitated; the first cavity mirror and the second cavity mirror are respectively positioned at the incident end and the signal light output end of the pumping light, and signal light single resonance output is realized through selection of the first cavity mirror and the second cavity mirror coating film, wherein the high reflection cavity mirror is coated with a signal light high reflection film and a pumping light and idler frequency light high transmission film, the coupling output rate of the coupling output mirror to the signal light is 5% -10%, the pumping light is coated with the high reflection film, and the idler frequency light is coated with the high transmission film.
Example 1
In this embodiment, the optical parametric oscillator with a partially unstable cavity structure includes a first cavity mirror 1, a first cylindrical mirror 2, a thin strip nonlinear optical crystal 3, a second cylindrical mirror 4, a second cavity mirror 5, pump light 6, signal light 7, and idler light 8. The size of the thin plate strip nonlinear optical crystal 3 is that the length is more than or equal to the width and is thicker, and the length multiplied by the width of the strip nonlinear crystal 1 is used as a horizontal plane; the cylindrical mirror I2 is a plane concave cylindrical reflector, and the bus is vertical to the horizontal plane; the second part of unstable cavity cylindrical mirror 4 is a plano-convex cylindrical mirror, and the bus is vertical to the horizontal plane; the first cavity mirror 1 is a circular plane mirror, is high in transmission of the pump light 6 and the idler light 8 and is high in reflection of the signal light 7; the second cavity mirror 5 is a circular plane mirror and is high in reflection to the pump light 6;
the pump light 6 is injected into the optical parametric oscillator through the first cavity mirror 1, and the thin strip nonlinear optical crystal 3, the first cylindrical mirror 2 and the second cylindrical mirror 4 form a part of unstable cavity structure with the geometric magnification of M in the horizontal direction and the stable cavity in the vertical direction; the injected pump light 6 passes through the thin plate strip nonlinear optical crystal 3 through multiple reflections between the cylindrical mirror I2 and the cylindrical mirror II 4, the horizontal direction of the light spot of the pump light 6 is amplified according to the geometric magnification M, the size of the light spot of the stable cavity is unchanged in the vertical direction, then the pump light 6 is reflected by the cavity mirror II 5 to return along the original light path, after the pump light passes through the thin plate strip nonlinear optical crystal 3 through multiple reflections between the cylindrical mirror I2 and the cylindrical mirror II 4, the horizontal direction of the light spot of the pump light 6 is reduced according to the geometric reduction 1/M, the size of the light spot of the stable cavity is unchanged in the vertical direction, and the pump light is output through the cavity mirror I1; because the thermal lens effect exists on the vertical plane of the thin strip nonlinear optical crystal, a stable cavity is formed on the vertical plane by the cavity structure formed by the thin strip nonlinear optical crystal, the cylindrical mirror I2 and the cylindrical mirror II 4, and the pump light 6 and the signal light 7 are restrained in the vertical direction; in the horizontal direction, the geometric magnification M of the cylindrical mirror I2 and the cylindrical mirror II 4 in the horizontal direction constrains the pump light 6 and the signal light 7, which is beneficial to improving the quality of the light beam; the signal light 7 is generated in the process that the pump light 6 passes through the thin plate strip nonlinear optical crystal 3 for many times, and is subjected to resonance enhancement in a resonant cavity formed by the first cavity mirror 1 and the second cavity mirror 5, so that high-efficiency high-beam quality output is realized; because the first part of the unstable cavity cylindrical lens, the second part of the unstable cavity cylindrical lens, the first cavity lens and the second cavity lens are plated with the film layer which is high in transmission of the idler light 8, the idler light 8 is lost out of the cavity after the generation of the accompanying signal light.
Example 2
In the embodiment, KTP crystal strip is used as a thin plate strip nonlinear optical crystal, the crystal size is 10mm multiplied by 15mm multiplied by 1mm (length multiplied by width multiplied by thickness), a crystal light-transmitting surface (15 mm multiplied by 1mm, width multiplied by thickness) is plated with 1064nm and 1572nm antireflection films, and a phase matching mode of the KTP strip crystal adopts (90 degrees, 0) non-critical phase matching; the wavelength of the injected pumping light is 1064nm, the pulse width is 10ns, the single pulse energy is 20mJ, the repetition frequency is 1kHz, and the spot size is 2mm multiplied by 0.8mm (width multiplied by height); the cylindrical mirror I and the cylindrical mirror II are respectively a plano-concave cylindrical mirror with the curvature R=550 mm and a plano-convex cylindrical mirror with the curvature R= -500mm to form a part of unstable cavity, the cavity length is 25mm, and the geometric magnification M is 1.1. As shown in fig. 3, the pump light is injected into a part of unstable cavity through a first cavity mirror, after the light passing surface of the KTP lath crystal is subjected to nonlinear frequency conversion of 5-pass, the light spot of the pump light is expanded from 2mm to 2.42mm under the action of the part of unstable cavity, and the light spot height is 0.8mm; under the reflection of the second cavity mirror, the pump light returns along the reverse light path and then is subjected to 5-path nonlinear frequency conversion and then is output to the optical parametric oscillator, in the process, the light spot of the pump light is contracted in a part of unstable cavity, the light spot width is changed from 2.42mm to 2mm, and the light spot height is still 0.8mm. Because the embodiment adopts a 1572nm signal light single resonance mode, the first cavity mirror is plated with a high-transmission film layer of pump light and idler frequency light, the coupling output rate of the second cavity mirror is 10 percent@signal light, and the second cavity mirror is plated with a high-transmission film layer of pump light and idler frequency light.
It will be readily appreciated by those skilled in the art that the foregoing description is merely a preferred embodiment of the invention and is not intended to limit the invention, but any modifications, equivalents, improvements or alternatives falling within the spirit and principles of the invention are intended to be included within the scope of the invention.
Claims (9)
1. An optical parametric oscillator with a partially unstable cavity structure is characterized by comprising a first cavity mirror (1), a first cylindrical mirror (2), a thin strip-shaped nonlinear optical crystal (3), a second cylindrical mirror (4) and a second cavity mirror (5) which are sequentially arranged along an optical path,
the pump light (6) is injected into the optical parametric oscillator through the cavity mirror I (1), the pump light (6) passes through the thin plate strip nonlinear optical crystal (3) in the process of being reflected by the cavity mirror I (2) and the cavity mirror II (4) for multiple times, in the process, the pump light (6) generates signal light (7) and idle frequency light (8), the coating film plated on the surfaces of the cavity mirror I (2), the cavity mirror II (4), the cavity mirror I (1) and the cavity mirror II (5) designs the idle frequency light (8) to throw the idle frequency light (8) out of the cavity for depletion, the light spots of the residual pump light (6) and the signal light (7) are amplified in the horizontal direction according to the geometric amplification rate M, the reflected pump light (6) and the amplified signal light (7) are reflected by the cavity mirror II (5) to return along an original light path, the pump light (6) is highly reflected, the signal light (7) is partially output, the coupling rate T is reduced to the signal light (7) and the light spots pass through the cavity mirror II (4) and the thin plate strip nonlinear optical crystal (3) in the horizontal direction, the light spots of the pump light (7) are reduced in the horizontal direction between the cavity mirror (6) and the thin plate strip nonlinear optical crystal (3), the vertical direction is limited by the stable cavity light spot size, the pumping light (6) is output through the first cavity mirror (1), the signal light (7) is subjected to resonance enhancement among the first cylindrical mirror (2), the sheet nonlinear optical crystal (3) and the second cylindrical mirror (4) in a resonant cavity formed by the first cavity mirror (1) and the second cavity mirror (5), and high-efficiency and high-beam quality output is realized.
2. An optical parametric oscillator of partially unstable resonator structure according to claim 1, characterized in that the dimensions of the slab nonlinear optical crystal (3) are such that: the length is more than or equal to the width and is thicker than the thickness;
and the long-by-wide surface of the lath-shaped nonlinear optical crystal (3) is used as a horizontal plane.
3. An optical parametric oscillator with partially unstable resonator structure according to claim 2, characterized in that the slab nonlinear optical crystal (3) is KTP crystal or KTA crystal with non-critical phase matching.
4. The optical parametric oscillator with the partially unstable cavity structure according to claim 1, wherein the first cylindrical mirror (2) is a plano-concave cylindrical mirror, a bus of the first cylindrical mirror is perpendicular to a horizontal plane, and the second cylindrical mirror (4) is a plano-convex cylindrical mirror, and a bus of the second cylindrical mirror is perpendicular to the horizontal plane.
5. The optical parametric oscillator with the partially unstable resonator structure according to claim 4, wherein the curvatures of the first cylindrical mirror (2) and the second cylindrical mirror (4) are respectively R1 and R2, and the distances between the first cylindrical mirror (2) and the second cylindrical mirror (4) are (r1+r2)/2.
6. The partially unstable resonator structured optical parametric oscillator according to claim 5, wherein the geometric amplification ratio of the unstable resonator composed of the first cylindrical mirror (2) and the second cylindrical mirror (4) to the light beam is m= |r1/r2|, and the flat critical resonator composed of the first cylindrical mirror (2) and the second cylindrical mirror (4) is formed in the vertical plane direction in the presence of the thermal focal length of the slab nonlinear optical crystal (3) to limit the pump light (6) and the signal light (7) and idler light (8) generated by nonlinear conversion to the thickness direction of the slab nonlinear optical crystal (3).
7. An optical parametric oscillator with partially unstable resonator structure according to any one of claims 1-6, characterized in that the geometrical amplification M is 1.1-1.3 to limit the beam divergence of the pump light (6) and the signal light (7) in the horizontal direction.
8. The method for outputting laser by the optical parametric oscillator with the partially unstable cavity structure is characterized by comprising the following steps of:
step one, building an optical path system: in the horizontal direction, a first cavity mirror (1), a first cylindrical mirror (2), a thin strip-shaped nonlinear optical crystal (3), a second cylindrical mirror (4) and a second cavity mirror (5) are sequentially arranged along an optical path, wherein the thin strip-shaped nonlinear optical crystal (3) is arranged between the first cylindrical mirror (2) and the second cylindrical mirror (4);
step two, pump light (6) is injected into the optical parametric oscillator through the cavity mirror I (1), the pump light (6) passes through the thin plate strip nonlinear optical crystal (3) in the process of being reflected by the cylindrical mirror I (2) and the cylindrical mirror II (4) for multiple times, in the process, the pump light (6) generates signal light (7) and idler light (8), the idler light (8) is projected out of the cavity by the coating design idler light (8) plated on the surfaces of the cylindrical mirror I (2), the cylindrical mirror II (4), the cavity mirror I (1) and the cavity mirror II (5), the residual pump light (6) and the light spots of the signal light (7) are amplified in the horizontal direction according to the geometric amplification rate M, the vertical direction is limited by the stable cavity light spot size, the reflected pump light (6) and the amplified signal light (7) are reflected by the cavity mirror II (5) to return along the original light path, the cavity mirror II (5) is highly reflective to the pump light (6) and outputs the signal light (7) partially, the coupling output rate is T, the reflected pump light (6) and the signal light (7) are reflected between the cylindrical mirror II (4) and the cylindrical mirror I (2) for multiple times and pass through the thin plate strip nonlinear optical crystal (3), the light spots of the pump light (6) and the signal light (7) are reduced in the horizontal direction according to the geometric reduction rate 1/M, the vertical direction is limited by the stable cavity light spot size, the pumping light (6) is output through the first cavity mirror (1), the signal light (7) is subjected to resonance enhancement among the first cylindrical mirror (2), the sheet nonlinear optical crystal (3) and the second cylindrical mirror (4) in a resonant cavity formed by the first cavity mirror (1) and the second cavity mirror (5), and high-efficiency and high-beam quality output is realized.
9. The method for outputting laser light by an optical parametric oscillator with a partially unstable cavity structure according to claim 8, wherein in the second step, the geometric amplification factor M is 1.1-1.3, so as to limit the beam divergence degree of the pump light (6) and the signal light (7) in the horizontal direction.
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