A Raman amplification system

Abstract

The present invention discloses a Raman amplification system, which comprises: a pump source, which emits a Raman amplification signal with a wavelength of λ P The pump light is split into two beams by the spectrometer: one beam is used as the pump light of the Raman amplifier, which passes through the time delay device and the amplifier, and after the beam aperture adjustment and collimation of the first telescope device, passes through the first dichroic mirror at 45 degrees, and enters the Raman amplifier composed of the first Raman crystal, the first plane mirror, and the second plane mirror; the other beam is reflected by the third plane mirror and injected into the Raman oscillator to generate a wavelength of λ S The Stokes light of the Raman oscillator is composed of a fourth plane reflector, a second Raman crystal, and a concave reflector; the wavelength is λ S The Stokes light is adjusted and collimated by the second telescope device, reflected by the 45° second dichroic mirror and the first dichroic mirror, and then enters the Raman amplifier.

Description

Technical Field

[0001] The invention relates to a high-efficiency Raman amplification system. Background Art

[0002] The Raman effect is an important method for altering laser wavelength. The wavelength of Raman scattered light is affected by the wavelength of the pump light and the Raman frequency shift of the Raman medium, resulting in a wavelength range from the ultraviolet to the infrared. Commonly used Raman media include gaseous and crystalline Raman media. Compared to gaseous Raman media, crystalline Raman media offer advantages such as high Raman gain, high thermal conductivity, high damage threshold, and compact size.

[0003] In recent years, with the development of crystal preparation technology, Raman lasers using crystals as Raman media have been widely used in fields such as communications, transportation, measurement, medical treatment, and national defense. However, in application fields such as laser ranging, lidar, and free-space communication, crystal Raman lasers may not be able to balance the laser beam quality and output power (or energy). While achieving good beam quality, it is often at the expense of output power (or energy). Therefore, the output power (or energy) of the laser needs to be further amplified. The combination of Raman lasers and Raman amplifiers can ensure that the laser can obtain higher pulse energy or average power while having good beam quality. Therefore, Raman amplifiers have the potential to increase the propagation distance of lasers and have broad application prospects in fields such as laser ranging, lidar, and free-space communication. The traditional single-pass Raman amplifier structure is limited by the size of the Raman crystal, making it difficult to achieve high-efficiency Raman amplification. Summary of the Invention

[0004] The present invention provides a Raman amplification system that overcomes the technical shortcomings of the single-pass Raman amplifier described above, achieving high-efficiency Raman amplification and significantly increasing the output power of Raman lasers. The operating wavelengths range from ultraviolet and visible light to infrared, depending on the selected materials. Details are described below:

[0005] A Raman amplification system, comprising: a pump source,

[0006] The pump source emits a wavelength of λ P The pump light is split into two beams by a beam splitter: one beam, serving as the pump light for the Raman amplifier, passes through a time delay device and an amplifier, and after adjustment and collimation of the beam aperture of the first telescope device, passes through a first dichroic mirror at a 45° angle, and enters the Raman amplifier composed of a first Raman crystal, a first plane reflector, and a second plane reflector;

[0007] Another beam of light is reflected by the third plane mirror and injected into the Raman oscillator, generating a wavelength of λ SThe Stokes light of the Raman oscillator is composed of a fourth plane mirror, a second Raman crystal, and a concave mirror;

[0008] The wavelength is λ S The Stokes light is adjusted and collimated by the second telescope device, reflected by the 45° second dichroic mirror and the first dichroic mirror, and then enters the Raman amplifier.

[0009] Wherein, a first plane reflector and a second plane reflector are placed on the left and right sides of the first Raman crystal, the first plane reflector and the second plane reflector are parallel to each other, and are neither perpendicular to the optical axis nor parallel to the optical axis;

[0010] The first plane reflector and the second plane reflector both have high transmittance to the pump light and high reflectivity to the Stokes light.

[0011] The fourth plane reflector has high transmittance to the pump light and high reflectance to the Stokes light; the concave reflector has high reflectance to the pump light and has partial transmittance to the Stokes light.

[0012] The first Raman crystal and the second Raman crystal use the same type of Raman medium and have the same Raman frequency shift;

[0013] The difference between the reciprocal of the pump light wavelength and the reciprocal of the Stokes light wavelength is equal to the common Raman frequency shift of the first Raman crystal and the second Raman crystal.

[0014] The beneficial effects of the technical solution provided by the present invention are:

[0015] 1. The amplifier can achieve outputs of different wavelengths, output linewidths, and powers by selecting bulk crystals such as diamond and barium tungstate as Raman crystals;

[0016] 2. The present invention realizes a multi-pass Raman amplifier structure by using the first and second plane reflectors and the first Raman crystal, which does not require complex manufacturing processes and procedures, and can effectively extract pump light energy, thereby increasing the design freedom of the Raman amplifier and improving the energy extraction efficiency and Raman conversion efficiency;

[0017] 3. The present invention can control the number of oscillations of Stokes light in the amplifier by adjusting the placement angles of the first and second plane reflectors or the placement position of the second plane reflector, thereby maximizing the pump light extraction efficiency.

[0018] 4. The present invention can control the time interval between the Stokes seed light peak and the pump light peak by adjusting the time delay device, thereby achieving good coupling between the pump light and the Stokes light in the time domain, effectively extracting the energy of the pump light, and significantly improving the Raman conversion efficiency;

[0019] 5. Since the Stokes light passes through the first Raman crystal multiple times, the Stokes light interacts with the pump light multiple times in the time domain. The pump light energy is fully extracted within the duration of the pump light pulse and fully converted into Stokes light energy, achieving efficient Raman amplification.

[0020] 6. The present invention can break through the limitation of Raman crystal size, so that the pulse laser amplification technology based on stimulated Raman scattering is no longer limited by the Raman crystal size, and achieve high-efficiency, high-energy, and high-power Raman laser output;

[0021] 7. The pulse width of the pump source and seed source is adjustable. The pulse width of the pump source is adjustable. The pulse width of the pump light can be in the order of nanoseconds, microseconds, milliseconds, or seconds. It is necessary to ensure that before the end of the pump light pulse duration, the Stokes light can end the oscillation between the first and second plane mirrors, be emitted from the right end face of the first Raman crystal, and no longer be reflected by the second plane mirror.

[0022] 8. When the first and second plane reflectors are parallel to each other and neither perpendicular to nor parallel to the optical axis, the propagation direction of the outgoing Stokes light is parallel to the optical axis and perpendicular to the end face of the first Raman crystal. This greatly increases the design freedom of the Raman amplifier and reduces the difficulty of calculating the emission direction of the Raman amplified light. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the structure of a Raman amplification system;

[0024] Figure 2 Schematic diagram of the optical path of the Raman amplifier.

[0025] Attachment Figure 1 The components represented by the reference numerals are as follows:

[0026] 1: Pump source; 2: Spectrometer;

[0027] 3: time delay device; 4: amplifier;

[0028] 5: First telescope device; 6: First dichroic mirror;

[0029] 7: first plane reflector; 8: first Raman crystal;

[0030] 9: second plane reflector; 10: third plane reflector;

[0031] 11: fourth plane reflector; 12: second Raman crystal;

[0032] 13: concave reflector; 14: second telescope device;

[0033] 15: Second dichroic mirror.

[0034] Attachment Figure 2 In the figure, the acute angle between the first plane reflector 7 and the second plane reflector 9 and the vertical direction is θ. The rectangle AMLT is the longitudinal section of the first Raman crystal 8. The auxiliary lines are CD, DF, GN, PQ, RS, and JI. AB ⊥ BC, CD ⊥ AQ, DF ⊥ AM, GN ⊥ AM, PQ ⊥ AM, RS ⊥ TL, JI ⊥ RJ, BC / / DF, GN / / DF, NO = HK, and OM = KL. DETAILED DESCRIPTION

[0035] In order to make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention are described in further detail below.

[0036] Example 1

[0037] The embodiment of the present invention proposes a Raman amplification system based on Raman crystal materials, see Figure 1 , including: a pump source 1, a spectrometer 2, a time delay device 3, an amplifier 4, a first telescope device 5, a first dichroic mirror 6, a first plane mirror 7, a first Raman crystal 8, a second plane mirror 9, a third plane mirror 10, a fourth plane mirror 11, a second Raman crystal 12, a concave mirror 13, a second telescope device 14, and a second dichroic mirror 15.

[0038] Among them, the pump source 1 emits a wavelength of λ P The pump light is split into two beams by beam splitter 2. One beam, serving as the pump light for the Raman amplifier, passes through time delay device 3 and amplifier 4. After adjustment and collimation of the beam aperture by first telescope device 5, it passes through a 45-degree first dichroic mirror 6 and enters the Raman amplifier, which consists of a first Raman crystal 8, a first plane mirror 7, and a second plane mirror 9. Both first plane mirror 7 and second plane mirror 9 have high transmittance for the pump light and high reflectivity for the Stokes light.

[0039] Another beam of light is reflected by the third plane reflector 10 and injected into the Raman oscillator to generate a wavelength of λ S The Raman oscillator consists of a fourth plane reflector 11, a second Raman crystal 12, and a concave reflector 13. The fourth plane reflector 11 is highly transparent to the pump light and highly reflective to the Stokes light. The concave reflector 13 is highly reflective to the pump light and partially transmits the Stokes light. The wavelength is λ S The Stokes light is adjusted and collimated by the second telescope device 14, and after being reflected by the 45° second dichroic mirror 15 and the first dichroic mirror 6, enters the Raman amplifier composed of the first Raman crystal 8, the first plane mirror 7, and the second plane mirror 9.

[0040] The Raman amplifier consists of a first plane mirror 7, a first Raman crystal 8, and a second plane mirror 9. Both the first and second plane mirrors 7 and 9 are highly transparent to pump light and highly reflective to Stokes light. The pump light and Stokes light are co-injected into the Raman amplifier, and the time interval between the pump and Stokes light peaks can be controlled using a time delay device 3.

[0041] In the Raman amplifier, a first plane mirror 7 and a second plane mirror 9 are placed on either side of a first Raman crystal 8. The first plane mirror 7 and the second plane mirror 9 are parallel to each other and are neither perpendicular to nor parallel to the optical axis. When placing the first plane mirror 7 and the second plane mirror 9, to prevent them from completely obstructing the first Raman crystal 8, the upper edge of the first plane mirror 7 should be vertically below the upper edge of the first Raman crystal 8, and the lower edge of the second plane mirror 9 should be vertically above the lower edge of the first Raman crystal 8. The pump light is incident on the first Raman crystal 8 along the optical axis, and the Stokes light is incident on the first Raman crystal 8 from a position between the upper edge of the first plane reflector 7 and the upper edge of the first Raman crystal 8. The Stokes light is reflected multiple times between the first Raman crystal 8 and the second plane reflector 9 and passes through the first Raman crystal 8. The Stokes light and the pump light interact with each other in the first Raman crystal 8 to achieve high-efficiency Raman amplification. Finally, the amplified Stokes light is emitted from a position between the lower edge of the second plane reflector 9 and the lower right edge of the first Raman crystal 8.

[0042] Example 2

[0043] To achieve high-power Raman amplification, the Raman dielectric material must possess a high Raman gain coefficient and high thermal conductivity. Furthermore, to meet the requirements of different operating wavelengths and achieve high conversion efficiency, the material must have a wide transmission spectrum and minimize negative nonlinear effects. Raman crystal materials, such as diamond, have an extremely wide spectral transmission range and extremely high thermal conductivity, making them effective materials for high-power Raman amplifiers. The embodiments of the present invention utilize a crystal material with a high gain coefficient and high thermal conductivity as the Raman gain medium, achieving high-power Raman amplification.

[0044] In the Raman amplification system, the transmittance of beamsplitter 2 for pump light is greater than 0% and less than 100%, and the incident angle is 45°. The time delay device 3 consists of four 45° plane mirrors with high reflectivity for pump light. The first dichroic mirror 6 and the second dichroic mirror 15 both have a 45° incident angle, are highly transparent to pump light, and highly reflective to Stokes light. They are used to allow the incident pump light to pass through and reflect the Stokes light, thus regulating the optical path.

[0045] The first Raman crystal 8 and the second Raman crystal 12 need to use the same type of Raman medium and have the same Raman frequency shift Δv. The difference between the reciprocal of the pump light wavelength and the reciprocal of the Stokes light wavelength must be equal to the common Raman frequency shift Δv of the first Raman crystal 8 and the second Raman crystal 12, that is:

[0046] The first telescope device 5 and the second telescope device 14 respectively adjust the beam aperture and collimate the pump light and the Stokes light. It is necessary to make the waist radius of the collimated Stokes light smaller than the waist radius of the collimated pump light.

[0047] When the first plane reflector 7 and the second plane reflector 9 are parallel to each other and neither perpendicular nor parallel to the optical axis, the propagation direction of the outgoing Stokes light is parallel to the optical axis and perpendicular to the end face of the first Raman crystal 8. This significantly increases the design freedom of the Raman amplifier and reduces the difficulty of calculating the emission direction of the Raman amplified light.

[0048] Establish an annex Figure 2 The angles between the first plane reflector 7 and the second plane reflector 9 and the vertical direction are both θ. The rectangle AMLT is the longitudinal section of the first Raman crystal 8. Auxiliary lines are drawn: CD, DF, GN, PQ, RS, and JI. AB⊥BC, CD⊥AQ, DF⊥AM, GN⊥AM, PQ⊥AM, RS⊥TL, JI⊥RJ, BC / / DF, GN / / DF, NO=HK, OM=KL, and the refractive index of air is n Air The refractive index of the first Raman crystal 8 is n Crystal .

[0049] The proof process is as follows:

[0050] Because in △ABC, ∠BAC=θ, ∠ABC=90°

[0051] ∴∠ACB=90°-θ

[0052] ∵∠ACB+∠BCD=90°

[0053] ∴∠BCD=θ

[0054] ∵Reflection angle ∠BCD=Reflection angle ∠ECD

[0055] ∴∠ECD=θ

[0056] ∵BC / / EF

[0057] ∴∠CEF=∠BCE=∠BCD+∠ECD=2θ

[0058] ∵GN / / DF

[0059] ∴∠DEH=∠EHI

[0060] ∵n Air sin∠CEF=n Crystal sin∠DEH,n Air sin∠GHJ=n Crystal sin∠EHI

[0061] ∴∠GHJ=∠CEF=2θ

[0062] ∵∠GLH=θ,∠GHL=90°

[0063] ∴∠HGL=∠HGJ=90°-θ

[0064] Because in △GHJ, ∠GHJ+∠HGJ+∠GJH=180°, ∠GHJ=2θ, ∠HGJ=90°-θ

[0065] ∴∠GJH=90°-θ

[0066] ∵∠GJI=90°

[0067] ∴∠HJI=θ

[0068] ∵Reflection angle ∠HJI=Reflection angle ∠IJK=θ

[0069] ∴∠HJK=∠HJI+∠IJK=2θ

[0070] ∵∠GHJ=∠HJK=2θ

[0071] ∴GH / / JK

[0072] ∵GH / / JK, GH⊥HK

[0073] ∴JK⊥HK

[0074] The number of Stokes light oscillations within the amplifier, and thus the Raman conversion efficiency of the Raman amplifier, can be controlled by adjusting the placement angles of the first plane reflector 7 and the second plane reflector 9. Assume that the length of the first Raman crystal 8 is L, the width is W, and the angle between the first plane reflector 7 and the second plane reflector 9 and the vertical direction is θ. The calculation process is as follows:

[0075]

[0076] BC=AB tanθ

[0077]

[0078]

[0079] HL=NM=AM-AB-BE-EN

[0080]

[0081] Let HK = x

[0082]

[0083]

[0084] The solution is

[0085]

[0086] ∴The distance Stokes light descends in the vertical direction after one round trip is

[0087] BO=BE+EN+NO

[0088]

[0089]

[0090] ∴The number of round trips of Stokes light between the first plane reflector 7 and the second plane reflector 9 is

[0091] In order to maximize the number of oscillations of the Stokes light, requirements are put forward for the placement of the first plane reflector 7 and the second plane reflector 9.

[0092] Position of the first plane reflector 7: By controlling the vertical distance TS between the upper edge of the first plane reflector 7 and the upper edge of the first Raman crystal 8, the Stokes light can be incident on the first Raman crystal 8 at a position close to the upper edge in the pump light action region, that is: AB+ω S ≤TS <AB+BO-ω S The first plane reflecting mirror 7 can be brought into close contact with the first Raman crystal 8 by controlling the horizontal distance RS from the upper edge of the first plane reflecting mirror 7 to the left end of the first Raman crystal 8 , ie, RS = SL·tanθ.

[0093] Position of the second plane reflector 9: By controlling the vertical distance AP from the lower edge of the second plane reflector 9 to the upper edge of the first Raman crystal 8, the Stokes light can be emitted from a position close to the lower edge in the pump light action area, that is: AB+(N-1)·BO+ω S ≤AP <AB+N·BO-ω S The second plane reflector 9 can be brought into close contact with the first Raman crystal 8 by controlling the horizontal distance PQ from the lower edge of the second plane reflector 9 to the right end of the first Raman crystal 8 , ie, PQ = AP·tanθ.

[0094] Assume that the number of oscillations of Raman light is equal to Nmax The conversion efficiency of the Raman amplifier is the highest when . The Raman amplifier is simulated by the radiation transfer equation and the oscillation number N that can achieve the highest Raman conversion efficiency is calculated. max Then adjust the position of the second plane reflector 9 so that the oscillation number of the Raman light in the Raman amplifier is exactly equal to N max .

[0095] Adjust the position of the second plane reflector 9: By controlling the vertical distance AP from the lower edge of the second plane reflector 9 to the upper edge of the first Raman crystal 8, the Stokes light can be emitted from a position close to the lower edge in the pump light action area, that is: AB+(N max -1)·BO+ω S ≤AP <AB+N max BO-ω S The second plane reflector 9 can be brought into close contact with the first Raman crystal 8 by controlling the horizontal distance PQ from the lower edge of the second plane reflector 9 to the right end of the first Raman crystal 8 , ie, PQ = AP·tanθ.

[0096] Unless otherwise specified, the embodiments of the present invention do not limit the models of the components. Any component that can perform the above functions may be used.

[0097] Those skilled in the art will understand that the accompanying drawings are only a schematic diagram of a preferred embodiment, and the serial numbers of the embodiments of the present invention are only for description and do not represent the advantages or disadvantages of the embodiments.

[0098] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A Raman amplification system, characterized in that: The system includes: a pump source, The pump source emits a wavelength of λ P The pump light is split into two beams by a beam splitter: one beam, serving as the pump light for the Raman amplifier, passes through a time delay device and an amplifier, and after adjustment and collimation of the beam aperture of the first telescope device, passes through a first dichroic mirror at a 45° angle, and enters the Raman amplifier composed of a first Raman crystal, a first plane reflector, and a second plane reflector; Another beam of light is reflected by the third plane mirror and injected into the Raman oscillator, generating a wavelength of λ S The Stokes light of the Raman oscillator is composed of a fourth plane mirror, a second Raman crystal, and a concave mirror; The wavelength is λ S The Stokes light is adjusted and collimated by the second telescope device, reflected by the second dichroic mirror and the first dichroic mirror at 45°, and then enters the Raman amplifier. Among them, a first plane mirror and a second plane mirror are placed on the left and right sides of the first Raman crystal. The first plane mirror and the second plane mirror are parallel to each other, neither perpendicular to the optical axis nor parallel to the optical axis. The first plane mirror and the second plane mirror are both highly transparent to the pump light and highly reflective to the Stokes light.

2. A Raman amplification system according to claim 1, characterized in that: The fourth plane reflector has high transmittance to the pump light and high reflectance to the Stokes light; the concave reflector has high reflectance to the pump light and has partial transmittance to the Stokes light.

3. A Raman amplification system according to claim 2, characterized in that: The first Raman crystal and the second Raman crystal use the same type of Raman medium and have the same Raman frequency shift; the difference between the reciprocal of the pump light wavelength and the reciprocal of the Stokes light wavelength is equal to the common Raman frequency shift of the first Raman crystal and the second Raman crystal.

4. A Raman amplification system according to claim 3, characterized in that: The pump source is a solid pulse laser, a semiconductor laser or a fiber laser, and the pump light is linearly polarized light; Both the first and second telescope devices consist of two convex lenses, whose light-transmitting surfaces are coated with a dielectric film that increases the transmittance of the input light. Both the first and second telescope devices have beam collimation functions. The first telescope device adjusts and collimates the beam aperture of the pump light, while the second telescope device adjusts and collimates the beam aperture of the Stokes light.

5. A Raman amplification system according to claim 4, characterized in that: The Stokes light propagates forward through the first Raman crystal, is reflected by the second plane reflector, and is converted into Stokes light propagating backward, which passes through the first Raman crystal again. The Stokes light propagating backward is reflected by the first plane reflector and is converted into Stokes light propagating forward again, which passes through the first Raman crystal again. This process continues in a cycle until the vertical position of the Stokes light propagating forward is lower than the lower edge of the second plane reflector, and the cycle stops. The Stokes light propagating forward is emitted from the right end face of the first Raman crystal and is no longer reflected by the second plane reflector.

6. A Raman amplification system according to claim 5, characterized in that: One end face of the dichroic mirror is coated with a dielectric film that increases the transmittance of pump light, and the other end face is coated with a dielectric film that is highly reflective of Stokes light.

7. A Raman amplification system according to claim 6, characterized in that: The time delay device is composed of four plane reflectors with an incident angle of 45 degrees each. The four plane reflectors are highly reflective to the pump light.

8. The Raman amplification system according to claim 7, characterized in that: The transmittance of the beam splitter to the pump light is greater than 0 and less than 100%, and the incident angle is 45°.

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