Raman beam combination laser amplifier

Abstract

The invention discloses a Raman beam combination laser amplifier, relates to the technical field of laser, and aims to solve the problem of low conversion efficiency of an existing beam combination laser amplifier. A first bowl-shaped reflecting mirror and a second bowl-shaped reflecting mirror are coaxially arranged at the two ends of a columnar reflecting mirror assembly, the concave surfaces face the columnar reflecting mirror assembly, and a Raman laser crystal is arranged in the columnar reflecting mirror assembly; seed light output by the seed light module enters the Raman laser crystal through the center of the first bowl-shaped reflector; and a plurality of beams of fundamental frequency light output by the plurality of fundamental frequency light modules are obliquely incident to the Raman laser crystal from the side surface of the columnar reflector assembly. Each beam of fundamental frequency light of the Raman beam combination laser amplifier can be reflected for multiple times in the amplifier and interacts with the seed light for multiple times, the conversion efficiency of the single beam of fundamental frequency light is improved, the adjustment difficulty of the fundamental frequency light module is low, and the Raman beam combination laser amplifier is suitable for integrated use.

Description

Technical Field

[0001] This invention relates to the field of laser technology, and more specifically to solid-state laser amplifiers. Background Technology

[0002] Since their invention, lasers have been widely used in various fields. The output power of a laser is a crucial performance parameter in laser applications, and researchers have conducted comprehensive studies to achieve higher laser output. The most direct approach is to increase the laser's input power. However, as the input power increases, the laser generates severe thermal effects. When this damage threshold is exceeded, the laser device will be damaged. Furthermore, the conversion efficiency of a single laser crystal has a saturation upper limit. To further achieve higher laser output, laser amplifiers have been developed.

[0003] A laser amplifier works by directing the seed light to be amplified onto a laser crystal, converting the incident fundamental frequency light into seed light to achieve laser power amplification. Since the seed light needs to pass through, the amplifier does not have a resonator. Therefore, multi-pass laser amplification technology has been developed. This involves utilizing the characteristics of polarized light to allow the laser to pass through the laser crystal multiple times for gain conversion and amplification; or passing the laser through multiple laser crystals, with each pass involving a gain conversion from fundamental frequency to seed light, achieving amplification; or by directing the seed light onto the laser crystal at a specific angle and reflecting it through a mirror, allowing it to pass through the crystal multiple times to increase laser gain and amplify the seed light. While coaxial multi-pass amplification offers high conversion efficiency, it increases local power density and thermal effects, potentially damaging the equipment if the crystal's damage threshold is exceeded. Furthermore, directing the light at a specific angle requires precise control of the resonant cavity, making its implementation quite challenging.

[0004] Unlike multi-beam laser amplifiers, which couple and amplify multiple fundamental frequency beams into a single seed beam, multiplying the fundamental frequency beams by increasing the number of fundamental frequency beams rather than the number of times the seed beam passes through, thus improving gain and conversion efficiency. Currently, there are two main types of solid-state laser beam amplifiers: one couples multiple fundamental frequency beams through a specific matrix arrangement and incident angle into a laser crystal for single-path passage; the other increases the optical path of the fundamental frequency beam within the crystal by altering its shape, or by using complex resonator designs to achieve the same effect. The former places high demands on optical device adjustment and crystal growth dimensions and processing technology, while the latter increases the complexity and adjustment difficulty of the resonator as the fundamental frequency beam passes through the crystal more times, resulting in a limited number of fundamental frequency beam passes and relatively low conversion efficiency. Summary of the Invention

[0005] The purpose of this invention is to solve the problems of complex structure and low conversion efficiency of existing beam laser amplifiers, and to provide a Raman beam laser amplifier with simple structure, low adjustment difficulty and high conversion efficiency.

[0006] A Raman beam laser amplifier according to the present invention includes a first bowl-shaped reflector, a second bowl-shaped reflector, a cylindrical reflector assembly, a Raman laser crystal, a seed light module, and a plurality of fundamental frequency light modules. The first bowl-shaped reflector, the second bowl-shaped reflector, and the cylindrical reflector assembly are arranged coaxially. The first bowl-shaped reflector and the second bowl-shaped reflector are respectively located at both ends of the cylindrical reflector assembly, and the concave surfaces of the first bowl-shaped reflector and the second bowl-shaped reflector face the cylindrical reflector assembly. The Raman laser crystal is disposed inside the cylindrical reflector assembly. The seed light output from the seed light module is incident on the Raman laser crystal through the center of the first bowl-shaped reflector. A plurality of fundamental frequency light beams output from the plurality of fundamental frequency light modules are obliquely incident on the Raman laser crystal from the side of the cylindrical reflector assembly.

[0007] Optionally, the plurality of baseband optical modules are distributed circumferentially.

[0008] Optionally, the plurality of fundamental frequency beams are incident on the Raman laser crystal from one end of the cylindrical mirror assembly.

[0009] Optionally, the cylindrical mirror assembly includes two cylindrical mirrors, one end face of which has a groove, and the two ends of the Raman laser crystal are respectively embedded in the grooves of the two cylindrical mirrors.

[0010] Optionally, the incident angle of the fundamental frequency light entering the cylindrical reflector assembly is around 30 degrees or around 45 degrees.

[0011] Optionally, the incident angle of the fundamental frequency light entering the cylindrical mirror assembly is determined by the following method: according to the formula Calculate the total Raman gain The angle of incidence of the fundamental frequency light at its maximum ,in, The value is the Raman gain coefficient of the Raman laser crystal. For fundamental frequency optical power, The height of Raman laser crystal 3. It is half the length of the cylindrical mirror assembly. Let be the radius of curvature of the first bowl-shaped reflector and the second bowl-shaped reflector. As a consumption factor, Let be the cross-sectional area of ​​the fundamental frequency light beam.

[0012] Optionally, the Raman laser crystal is diamond, yttrium vanadate, potassium gadolinium tungstate, barium nitrate, or lithium iodate.

[0013] This invention uses two bowl-shaped and cylindrical reflectors to enable each fundamental frequency beam to be reflected multiple times inside the amplifier and interact with the seed beam multiple times. This amplifies the seed beam by approximately multiple non-collinear fundamental frequency beams. The structure is not only simple, but also increases the interaction volume between the fundamental frequency beam and the seed beam, improves the conversion efficiency of a single fundamental frequency beam, and allows the number of fundamental frequency beams to be further increased, ultimately forming a ring that enters from the side.

[0014] Furthermore, the baseband optical module of this invention is easy to adjust and suitable for integrated use. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the structure of a Raman beam laser amplifier according to an embodiment of this application;

[0016] Figure 2 This is a 45° assembly drawing of the amplifier section according to an embodiment of this application;

[0017] Figure 3 This is a longitudinal assembly view of the amplifier section according to an embodiment of this application;

[0018] Figure 4 This is a combination diagram of the amplifier section according to an embodiment of this application. Detailed Implementation

[0019] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, unless otherwise specified, the following embodiments and features described therein can be combined with each other.

[0020] As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context indicates otherwise. It should be further understood that the terms “comprising,” “including,” indicate the presence of the stated feature, operation, element, component, item, kind, and / or group, but do not preclude the presence, occurrence, or addition of one or more other features, operations, elements, components, items, kinds, and / or groups. The terms “or” and “and / or” as used herein are interpreted as inclusive, or mean any one or any combination thereof. Thus, “A, B, or C” or “A, B, and / or C” means “any one of: A; B; C; A and B; A and C; B and C; A, B, and C.” Exceptions to this definition occur only when combinations of elements, functions, or operations are inherently mutually exclusive in some manner.

[0021] To address the problem of low conversion efficiency in existing beam laser amplifiers, this invention provides a Raman beam laser amplifier that can improve the conversion efficiency of fundamental frequency light.

[0022] Figure 1 This is a schematic diagram of the structure of a Raman beam laser amplifier according to an embodiment of this application. Figure 1 As shown, the Raman beam laser amplifier of this application embodiment includes a seed light module, multiple fundamental frequency light modules, and an amplification section.

[0023] like Figures 2 to 4 As shown, the magnification section includes a first bowl-shaped mirror 1, a second bowl-shaped mirror 5, a cylindrical mirror assembly, and a Raman laser crystal 3, all arranged coaxially. The first bowl-shaped mirror 1 and the second bowl-shaped mirror 5 are located at opposite ends of the cylindrical mirror assembly, with the concave surfaces of both mirrors facing the assembly. The Raman laser crystal 3 is disposed inside the cylindrical mirror assembly. The cylindrical mirror assembly can consist of two cylindrical mirrors (a first cylindrical mirror 2 and a second cylindrical mirror 4), each with a groove on one end face. A portion of the Raman laser crystal 3 is embedded in the groove of the first cylindrical mirror 2, and the other portion is embedded in the groove of the second cylindrical mirror 4.

[0024] The seed light module includes a seed light source 8 and a seed light coupling lens group 9. The seed light source 8 is used to generate seed light. The seed light coupling lens group 9 adjusts the divergence angle and beam diameter of the seed light through the lens group. The lens group can select a combination of two positive lenses or a combination of one positive lens and one negative lens according to the divergence of the seed light. The adjusted seed light is incident on the amplification section through the center of the end face of the first bowl-shaped reflector 1 and enters the Raman laser crystal 3.

[0025] The fundamental frequency light module includes a fundamental frequency light source 6 and a fundamental frequency light coupling lens group 7. The fundamental frequency light source 6 is used to generate fundamental frequency light. The fundamental frequency light coupling lens group 7 adjusts the divergence angle and beam diameter of the fundamental frequency light through the lens group. The lens group can select a combination of two positive lenses or a combination of one positive lens and one negative lens according to the divergence of the fundamental frequency light. The adjusted fundamental frequency light is obliquely incident on the Raman laser crystal 3 from the side of the cylindrical reflector assembly.

[0026] In one implementation, the first bowl-shaped reflector 1 and the second bowl-shaped reflector 5 have the same shape and size, both having spherical sides. The opening sides of the first bowl-shaped reflector 1 and the second bowl-shaped reflector 5 face the cylindrical reflector assembly, and the diameter of the opening side is 2. The first cylindrical reflector 2 and the second cylindrical reflector 4 are of the same length and are adjustable. Their end faces are both circular, with a diameter of 2. On the contact surface of the first cylindrical mirror 2 and the second cylindrical mirror 4, there is a 3 mm... A rectangular groove with a diameter of 3 mm and a depth of 3.5 mm is formed. The Raman laser crystal 3 is embedded in two rectangular grooves. The Raman laser crystal 3 can be a single crystal or multiple crystals arranged side by side. The size of the Raman laser crystal 3 should match the rectangular grooves, ideally filling them completely. The sides of the first bowl-shaped reflector 1 and the second bowl-shaped reflector 5 are coated with a high-reflection film for fundamental frequency light, and the bottom surfaces are coated with a high-transmittance film for both seed light and fundamental frequency light. The sides of the first cylindrical reflector 2 and the second cylindrical reflector 4 are coated with a high-reflection film for fundamental frequency light. The two end faces of the first cylindrical reflector 2 and the two end faces of the second cylindrical reflector 4 are coated with a high-transmittance film for both seed light and fundamental frequency light. A high-transmittance film 10 for fundamental frequency light is coated on the side of the first cylindrical reflector 2, near the first bowl-shaped reflector 1. The Raman laser crystal 3 can be any one of diamond, yttrium vanadate, potassium gadolinium tungstate, barium nitrate, or lithium iodate. The sides of the Raman laser crystal 3 are coated with a high-transmittance film for both fundamental frequency light and seed light.

[0027] The two cylindrical mirrors, as well as the cylindrical mirror and the bowl-shaped mirror, can be bonded together with optical adhesive or assembled with external fixing brackets.

[0028] Seed light source 8 is arranged on the central axis of the magnified part ( Figure 1 In the direction indicated by the horizontal arrow, the seed light with a wavelength of 1240 nm output is shaped by the seed light coupling lens group 9, enters the amplification part from the end face of the first bowl-shaped mirror 1, propagates along the central axis of the amplification part and passes through the Raman laser crystal 3, and finally exits from the end face of the second bowl-shaped mirror 5.

[0029] The fundamental frequency light source 6 is arranged on the side of the seed light source 8 and the amplification section. Its output fundamental frequency light with a wavelength of 1064 nm is shaped by the fundamental frequency light coupling lens group 7 and obliquely incident on the amplification section from the junction of the first cylindrical mirror 2 and the first bowl-shaped mirror 1 (the position coated with the fundamental frequency light high-transmittance film 10). Inside the cylindrical mirror assembly, the fundamental frequency light is continuously reflected multiple times on the inner surfaces of the first cylindrical mirror 2 and the second cylindrical mirror 4 until it is incident on the side wall of the second bowl-shaped mirror 5. Since the side wall of the bowl-shaped mirror is spherical, the incident angle is reduced compared to the incident angle on the cylindrical mirror assembly. After two consecutive reflections on the side wall of the second bowl-shaped mirror 5, the fundamental frequency light propagates to the first bowl-shaped mirror 1. The fundamental frequency light propagates back and forth multiple times in the amplification section. Since the sidewall of the bowl-shaped mirror is a concave sphere, according to the law of reflection of spherical optics, when light is incident on the concave mirror, the normal points to the center of the sphere. Each reflection of the light on the concave sidewall produces a deflection component parallel to the central axis. Therefore, it has the characteristic of converging the incident light towards the central axis. So after multiple reflections, the vertical component of the light propagation vector gradually transforms into the horizontal component, causing the light to tend to propagate along the central axis. This is manifested as the reflection angle of the fundamental frequency light gradually decreasing on the sidewall of the bowl-shaped mirror, while the reflection angle in the cylindrical mirror will become larger and larger, eventually tending towards the central axis. As the light travels along the central axis and converges towards the central axis, the position of the light in space gradually approaches the central axis, and finally exits from the end face of the first bowl-shaped mirror 1 or the second bowl-shaped mirror 5.

[0030] by Figure 1 For example, the fundamental frequency light propagating from left to right is called the forward fundamental frequency light 11, and the fundamental frequency light propagating from right to left is called the reverse fundamental frequency light 12. According to... Figure 1 It is known that when the forward fundamental frequency light 11 is incident on the side wall of the second bowl-shaped reflector 5, it is reflected twice on the side wall of the second bowl-shaped reflector 5 to form the reverse fundamental frequency light 12. Due to the spherical reflection characteristics of the side wall of the bowl-shaped reflector, the incident angle of the reverse fundamental frequency light 12 on the side wall of the cylindrical reflector assembly is smaller than that of the forward fundamental frequency light 11 on the side wall of the cylindrical reflector assembly. Moreover, the incident point of the fundamental frequency light on the bowl-shaped reflector will be closer to the central axis each time than the previous time. Therefore, during the multiple round trips of the fundamental frequency light in the cylindrical reflector assembly, the incident angle on the side wall of the cylindrical reflector assembly will gradually increase, and finally be incident on the end face of the bowl-shaped reflector in a direction that tends to be parallel to the central axis, and exit from the end face of the bowl-shaped reflector.

[0031] In practical applications, multiple fundamental frequency optical modules can be evenly arranged on the side of the amplified part along the circumference, and the resulting multiple fundamental frequency beams can be simultaneously incident from different positions of the fundamental frequency high-transmittance film 10 at the same angle to form a ring array, so as to make full use of the space of the cylindrical reflector assembly.

[0032] The fundamental frequency photon is incident on Raman laser crystal 3 and undergoes inelastic collisions with phonons in Raman laser crystal 3, resulting in a frequency of The fundamental frequency light excites a large number of molecules to the "virtual" energy level u, resulting in population inversion, followed by stimulated emission, producing a frequency of... The first-order Stokes light. If the above process is repeated with the first-order Stokes light as the fundamental frequency, higher-order Stokes light can be generated. This embodiment of the application utilizes this characteristic of the Raman laser crystal 3 to achieve power amplification of the seed light.

[0033] To obtain a higher Raman gain, the incident angle of the fundamental frequency light needs to be carefully selected. Since the reflectivity of the high-reflectivity coating is a function of wavelength and incident angle, the incident angle shift caused by the bowl-shaped mirror will lead to a shift in the center wavelength of the high-reflectivity coating, resulting in increased loss of the fundamental frequency light. Considering the coating cost while keeping the high-reflectivity bandwidth constant, the incident angle... You can choose the common 30° and 45° range.

[0034] This application provides a method for selecting the optimal incident angle of fundamental frequency light. Let the length of the cylindrical mirror assembly (with the length direction being the central axis direction) be 2. The width and height of Raman laser crystal 3 are (That is, the cross-section is square, and the side length is...) The Raman gain coefficient of Raman laser crystal 3 is The incident angle of the fundamental frequency light on the cylindrical mirror is The radius of the bowl-shaped mirror is The fundamental frequency optical power is The cross-sectional area of ​​the fundamental frequency light is When incident at an oblique angle, the overlap factor of the pump light (i.e., the fundamental frequency light) and the signal light (i.e., the seed light) is: The fundamental rate equation for Raman amplification is the signal light power. With interaction length rate of change :

[0035]

[0036] in, Let be the coordinates of the propagation path of the fundamental frequency light. For the signal light at position The power at that point. Integrating the above equation, we obtain the Raman gain generated when the fundamental frequency light first passes through Raman laser crystal 3. for:

[0037]

[0038] The fundamental frequency light is first incident on the second bowl-shaped mirror 5, and the number of reflections on the cylindrical mirror is: This is considered to be the same number of times the light passes through Raman laser crystal 3. Each time the light passes through Raman laser crystal 3, the fundamental frequency light is converted into signal light, resulting in energy consumption; therefore, a consumption factor is introduced. The gain is defined as the ratio of the gain of the (n+1)th pass through Raman laser crystal 3 to the gain of the nth pass through Raman laser crystal 3. Ignoring the residual gain resulting from the fundamental frequency light being reflected by the second bowl-shaped mirror 5 and then re-entering Raman laser crystal 3, the total Raman gain for the entire amplification process is... for:

[0039]

[0040] Based on the parameters under actual conditions, numerical methods such as Newton-Raphson iteration can be used to calculate the results. Maximum angle of incidence This angle of incidence This is called the optimal incident angle. Compared to the conventional 30° and 45° incident angles, the optimal incident angle selected by the above method can obtain a greater Raman gain.

[0041] This application proposes a Raman beamed laser amplifier that combines the advantages of multi-pass traveling wave amplification with the basic technology of beamed amplification, which can significantly improve the conversion efficiency of fundamental frequency light and fill the technological gap of Raman amplifiers.

Claims

1. A Raman beam laser amplifier, characterized in that, It includes a first bowl-shaped reflector, a second bowl-shaped reflector, a cylindrical reflector assembly, a Raman laser crystal, a seed light module, and several fundamental frequency light modules; The first bowl-shaped reflector, the second bowl-shaped reflector, and the cylindrical reflector assembly are arranged coaxially. The first bowl-shaped reflector and the second bowl-shaped reflector are located at opposite ends of the cylindrical reflector assembly, and the concave surfaces of the first bowl-shaped reflector and the second bowl-shaped reflector face the cylindrical reflector assembly. The Raman laser crystal is arranged inside the cylindrical reflector assembly. The seed light output by the seed light module is incident on the Raman laser crystal through the center of the first bowl-shaped reflector; the several beams of fundamental frequency light output by the several fundamental frequency light modules are incident obliquely on the Raman laser crystal from the side of the cylindrical reflector assembly.

2. The Raman beam laser amplifier as described in claim 1, characterized in that, The plurality of baseband optical modules are distributed circumferentially.

3. The Raman beam laser amplifier as described in claim 2, characterized in that, The plurality of fundamental frequency beams are incident from one end of the cylindrical mirror assembly onto the Raman laser crystal.

4. The Raman beam laser amplifier as described in any one of claims 1 to 3, characterized in that, The cylindrical mirror assembly includes two cylindrical mirrors, each with a groove on one end face, and the two ends of the Raman laser crystal are respectively embedded in the grooves of the two cylindrical mirrors.

5. The Raman beam laser amplifier as described in claim 3, characterized in that, The incident angle of the fundamental frequency light entering the cylindrical reflector assembly is around 30 degrees or around 45 degrees.

6. The Raman beam laser amplifier as described in claim 3, characterized in that, The incident angle of the fundamental frequency light entering the cylindrical mirror assembly is determined in the following way: According to the formula Calculate the total Raman gain The angle of incidence of the fundamental frequency light at its maximum ,in, The value is the Raman gain coefficient of the Raman laser crystal. For fundamental frequency optical power, The height of Raman laser crystal 3. It is half the length of the cylindrical mirror assembly. Let be the radius of curvature of the first bowl-shaped mirror and the second bowl-shaped mirror. As a consumption factor, Let be the cross-sectional area of ​​the fundamental frequency light beam.

7. The Raman beam laser amplifier as described in claim 3, characterized in that, The Raman laser crystal is made of diamond, yttrium vanadate, potassium gadolinium tungstate, barium nitrate, or lithium iodate.

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