An eight-way pulse stretcher

Abstract

This application provides an eight-channel pulse stretcher, including a circulator, a collimator, a polarization beam splitter, a two-pass transmission-type single-grating stretching unit, a beam-shrinking unit, a quarter-wave plate, a first 0-degree reflector, and a second 0-degree reflector. The pulse stretcher of this application achieves a large pulse stretching by having the pulse pass through the two-pass transmission-type single-grating stretching unit four times. This is simpler, more reliable, and more practical than existing active-switching methods, and avoids the problem of increased amplification noise at the back end of the pulse stretcher. The pulse stretcher of this application has a compact structure, high stability, and does not require switching control. It can stretch pulses to the nanosecond level, making it very suitable for the stretching and amplification of high-energy pulses. The pulse stretcher of this application uses a circulator and collimator to realize the fiber input and output of the optical pulse, greatly improving the stretcher's accessibility and making it very suitable for embedding in high-energy laser systems.

Description

Technical Field

[0001] This application belongs to the field of laser technology, and more specifically, relates to an eight-channel pulse stretcher. Background Technology

[0002] Chirped pulse amplification (CPA) is a commonly used technique in the field of high-energy ultrafast lasers. The pulse needs to be broadened using a stretcher, and how to obtain a stretcher with high broadening capacity at a relatively low cost and with a compact structure has always been a research topic in CPA technology.

[0003] Chinese patents CN102866557B and CN109407354A achieve multiple pulse broadening within the stretcher by introducing an electro-optic switch, while Chinese patent CN103001107A achieves the same by introducing an acousto-optic modulator. Their common feature is that they achieve multiple pulse broadening through active switching control. This method places very high demands on the components and electrical control, and is highly susceptible to small pulses, leading to increased noise in the downstream amplification. Summary of the Invention

[0004] The purpose of this application is to provide an eight-channel pulse stretcher to solve the technical problem in the prior art where multiple stretching of the pulse in the stretcher through active switching control leads to increased noise in the back-end amplification.

[0005] To achieve the above objectives, the technical solution adopted in this application is: to provide an eight-channel pulse stretcher, including a circulator, a collimator, a polarization beam splitter, a two-channel transmission type single grating stretching unit, a beam shrinking unit, a quarter-wave plate, a first 0-degree reflector, and a second 0-degree reflector;

[0006] The light pulse is input from the input end of the circulator, collimated by the collimator, and then enters the polarization beam splitter to output first-state polarized light. The first-state polarized light pulse passes through the two-pass transmission type single grating broadening unit for the first time, and then passes through the beam shrinking unit, the quarter-wave plate and the first 0-degree reflector, and the first-state polarized light pulse is transformed into second-state polarized light.

[0007] The second state polarized light pulse passes through the two-pass transmission type single grating broadening unit for the second time, and the second state polarized light pulse returns after passing through the polarization beam splitter and the second 0-degree reflector.

[0008] The returning light pulse passes through the two-pass transmission single grating broadening unit for the third time, and then passes through the beam shrinking unit, the quarter-wave plate, and the first 0-degree reflector again, and the second state polarized light pulse is transformed into the first state polarized light pulse;

[0009] The first state polarized light pulse passes through the two-pass transmission type single grating stretching unit for the fourth time, then passes through the polarization beam splitter, is coupled into the circulator through the collimator, and is output from the output end of the circulator;

[0010] The first state polarized light is either horizontally polarized or vertically polarized, and the second state polarized light is perpendicular to the direction of the first state polarized light.

[0011] Furthermore, the two-way transmission type single grating stretching unit includes a transmission grating, a concave reflector and a plane reflector, with the transmission grating placed between the concave reflector and the plane reflector.

[0012] Furthermore, the transmission grating is insensitive to the polarization state of light.

[0013] Furthermore, the transmission grating includes two sub-transmission gratings and a half-wave plate, the half-wave plate being placed parallel between the two sub-transmission gratings.

[0014] Furthermore, the parameters of the two said transmission gratings are exactly the same.

[0015] Furthermore, the distance between the concave mirror and the planar mirror is equal to the focal length of the concave mirror.

[0016] Furthermore, the beam-shrinking unit includes a convex cylindrical mirror and a concave cylindrical mirror arranged in parallel.

[0017] Furthermore, the convex cylindrical mirror and the concave cylindrical mirror are set to have a common focal length.

[0018] Furthermore, the polarization beam splitter is a polarization beam splitter flat plate or a polarization beam splitter prism.

[0019] Furthermore, the collimator is an aspherical lens.

[0020] Compared with the prior art, this application has the following technical effects:

[0021] This application discloses an eight-pass pulse stretcher that alters the polarization state of an optical pulse through a quarter-wave plate and a first and second 0-degree reflector. Combined with a polarization beam splitter, this allows the pulse to pass through a two-pass transmission-type single-grating stretching unit four times, thereby achieving a large pulse stretching. This method is simpler, more reliable, and more practical than existing active switching methods, and avoids the problem of increased amplification noise at the back end of the pulse stretcher. The pulse stretcher of this application has a compact structure, high stability, and requires no switching control. It can stretch pulses to the nanosecond level, making it ideal for high-energy pulse stretching and amplification.

[0022] The pulse stretcher of this application uses a circulator and a collimator to realize the optical fiber input and output of optical pulses, which greatly improves the accessibility of the stretcher and makes it very suitable for embedding in high-energy laser systems. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of the structure of an eight-channel pulse stretcher provided in an embodiment of this application;

[0025] Figure 2 This is a schematic diagram of the structure of a transmission grating provided in an embodiment of this application.

[0026] The following are the labeling elements in the figure:

[0027] 1. Circulator first port; 2. Circulator; 3. Circulator second port; 4. Collimator; 5. Polarizing beam splitter; 6. Transmission grating; 7. Concave mirror; 8. Plane mirror; 9. Convex cylindrical mirror; 10. Concave cylindrical mirror; 11. Quarter-wave plate; 12. First 0-degree mirror; 13. Second 0-degree mirror; 14. Circulator third port; 601. Transmission grating; 602. Half-wave plate. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this application clearer, the embodiments of this application will be further described below in conjunction with the accompanying drawings. The following description presents a preferred embodiment among several possible embodiments of this application, intended to provide a basic understanding of the application, but not to identify key or decisive elements of the application or to limit the scope of protection sought.

[0029] In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values.

[0030] Techniques, methods, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and equipment should be considered part of the specification.

[0031] It should be noted that similar labels and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be discussed further in subsequent figures. Also, it should be understood that, for ease of description, the dimensions of the various parts shown in the figures are not drawn to actual scale.

[0032] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as being "connected to" another component, it can be directly connected to or indirectly connected to that other component.

[0033] It should be understood that the terms "length", "upper", "lower", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0034] Furthermore, the terms "first," "second," "third," "fourth," and "fifth" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first," "second," "third," "fourth," or "fifth" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0035] Please refer to the following: Figure 1 , Figure 2 The present application will now describe an eight-channel pulse stretcher provided in the embodiments of this application.

[0036] The embodiment of this application provides an eight-channel pulse stretcher, which mainly includes a circulator 2, a collimator 4, a polarization beam splitter 5, a two-channel transmission type single grating stretching unit, a beam shrinking unit, a quarter-wave plate 11, a first 0-degree reflector 12, and a second 0-degree reflector 13.

[0037] like Figure 1 As shown, a mode-locked pulsed laser with a center wavelength of 1030 nm, a linewidth of 20 nm, a pulse width of 3 ps, a repetition rate of 80 MHz, and a power of 10 mW is input from the first port 1 (input end) of the circulator, output from the second port 3 of the circulator, and collimated by collimator 4. Collimator 4 is an aspherical lens with a focal length of 8 mm, and the collimated output spot is approximately 1.8 mm. The pigtail of circulator 2 is a panda-type polarization-maintaining fiber, and the pulse polarization state output by collimator 4 is vertical (S) polarization.

[0038] Continue as Figure 1 As shown, the polarization beam splitter 5 is a polarization beam splitting prism or polarization beam splitting plate, reflecting vertically (S) polarized light and transmitting horizontally (P) polarized light, with an extinction ratio greater than 3000:1. The collimated vertically (S) polarized light, after being reflected by the polarization beam splitter 5, enters the two-pass transmission single-grating broadening unit. It should be noted that the light intensity of the first 0-degree reflector 12, the quarter-wave plate 11, and the beam-shrinking unit is lower than that of the vertically (S) polarized light reflected by the polarization beam splitter 5; this pulse can pass unobstructed through these devices into the two-pass transmission single-grating broadening unit.

[0039] The two-pass transmission-type single-grating broadening unit of this application embodiment includes a transmission grating 6, a concave mirror 7, and a plane mirror 8, with the transmission grating 6 positioned between the concave mirror 7 and the plane mirror 8. Its basic optical path is as follows: the reflected collimated light enters the transmission grating 6 and undergoes the first diffraction; the diffracted light is collimated and reflected by the concave mirror 7 and then reflected by the plane mirror 8, and again reflected by the concave mirror 7 before entering the transmission grating 6 for the second diffraction. It should be noted that the light height of the first diffracted light is the same as that of the vertically (S) polarized light reflected by the polarization beam splitter 5, and is higher than that of the second diffracted light.

[0040] In the two-pass transmission type single grating broadening unit, the distance between the transmission grating 6 and the concave mirror 7 is 215mm, the focal length of the concave mirror 7 is 445mm, the distance between the concave mirror 7 and the plane mirror 8 is equal to the focal length of the concave mirror 7, and the dispersion is 23.2ps / nm.

[0041] The light pulse passing through the two-pass transmission single-grating broadening unit for the first time is still vertically (S) polarized light, and the light spot is elliptical collimated light, with the major axis of the ellipse perpendicular to the grating scribe line direction. This light spot passes through the beam-shrinking unit, where the major axis of the light spot is reduced in size, and the output remains collimated light. In this embodiment, the beam-shrinking unit consists of a parallel convex cylindrical mirror 9 and a concave cylindrical mirror 10, with the two cylindrical mirrors sharing a common focal length. The vertically (S) polarized light, after passing through the quarter-wave plate 11, the first 0-degree reflecting mirror 12, and the quarter-wave plate 11, becomes horizontally (P) polarized light, and then passes in the opposite direction through the beam-shrinking unit into the two-pass transmission single-grating broadening unit.

[0042] The second light pulse passing through the two-pass transmission single grating stretching unit is horizontal (P) polarized light. After being transmitted through the polarization beam splitter 5, it is reflected by the second 0-degree reflector 13 and then transmitted through the polarization beam splitter 5 again before entering the two-pass transmission single grating stretching unit.

[0043] The third light pulse passing through the two-pass transmission single grating broadening unit is horizontal (P) polarized light. After passing through the beam shrinking unit, then through the quarter-wave plate 11, the first 0-degree reflector 12 and the quarter-wave plate 11, it becomes vertical (S) polarized light. Then it passes in the opposite direction through the beam shrinking unit and enters the two-pass transmission single grating broadening unit.

[0044] The fourth light pulse passing through the two-pass transmission single grating stretching unit is vertically (S) polarized light. After being reflected by the polarization beam splitter 5, it is coupled into the second port 3 of the circulator by the collimator 4, and then output as a stretched pulse from the third port 14 (output end) of the circulator.

[0045] An eight-pass pulse stretcher according to an embodiment of this application passes through a two-pass transmission single-grating stretching unit four times, and its dispersion is four times that of the two-pass transmission single-grating stretching unit, which is 92.8 ps / nm. A mode-locked pulse laser with a linewidth of 20 nm can be stretched to 1.85 ns.

[0046] Figure 2 This is a schematic diagram of the structure of the transmission grating 6 provided in an embodiment of this application. The transmission grating 6 consists of two sub-transmission gratings 601 and a half-wave plate 602, with the half-wave plate 602 placed parallel between the two sub-transmission gratings 601. The two sub-transmission gratings 601 have identical parameters, with dimensions of 110*40mm, a line count of 1730 / mm, and are suitable for a wavelength of 1030nm. When the light is vertically (S) polarized, the diffraction efficiency is greater than 95%, and when the light is horizontally (P) polarized, the diffraction efficiency is <0.25%. A polarization-insensitive grating with an efficiency greater than 90% is achieved through the two sub-transmission gratings 601 and the half-wave plate 602.

[0047] An eight-pass pulse stretcher according to an embodiment of this application changes the polarization state of the optical pulse through a quarter-wave plate 11, a first 0-degree reflector 12, and a second 0-degree reflector 13. Combined with a polarization beam splitter 5, the pulse passes through a two-pass transmission-type single-grating stretching unit four times, thereby achieving a large pulse stretching. This method is simpler, more reliable, and more practical than existing active switching methods, and avoids the problem of increased amplification noise at the back end of the pulse stretcher. The pulse stretcher of this embodiment has a compact structure, high stability, and does not require switching control. It can stretch pulses to the nanosecond level, making it very suitable for high-energy pulse stretching and amplification.

[0048] The pulse stretcher in this embodiment uses a circulator 2 and a collimator 4 to realize the optical fiber input and output of optical pulses, which greatly improves the accessibility of the stretcher and makes it very suitable for embedding in high-energy laser systems.

[0049] The above embodiments merely illustrate several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. An eight-channel pulse stretcher, characterized in that, It includes a circulator, collimator, polarization beam splitter, two-pass transmission type single grating broadening unit, beam shrinking unit, quarter-wave plate, first 0-degree reflector and second 0-degree reflector; The light pulse is input from the input end of the circulator, collimated by the collimator, and then enters the polarization beam splitter to output first-state polarized light. The first-state polarized light pulse passes through the two-pass transmission type single grating broadening unit for the first time, and then passes through the beam shrinking unit, the quarter-wave plate and the first 0-degree reflector, and the first-state polarized light pulse is transformed into second-state polarized light. The second state polarized light pulse passes through the two-pass transmission type single grating broadening unit for the second time, and the second state polarized light pulse returns after passing through the polarization beam splitter and the second 0-degree reflector. The returning light pulse passes through the two-pass transmission single grating broadening unit for the third time, and then passes through the beam shrinking unit, the quarter-wave plate, and the first 0-degree reflector again, and the second state polarized light pulse is transformed into the first state polarized light pulse; The first state polarized light pulse passes through the two-pass transmission type single grating stretching unit for the fourth time, then passes through the polarization beam splitter, is coupled into the circulator through the collimator, and is output from the output end of the circulator; The first state polarized light is either horizontally polarized or vertically polarized, and the second state polarized light is perpendicular to the direction of the first state polarized light. The two-way transmission type single grating stretching unit includes a transmission grating, a concave mirror, and a plane mirror, with the transmission grating positioned between the concave mirror and the plane mirror.

2. The eight-channel pulse stretcher as described in claim 1, characterized in that, The transmission grating is insensitive to the polarization state of light.

3. An eight-channel pulse stretcher as described in claim 2, characterized in that, The transmission grating includes two sub-transmission gratings and a half-wave plate, with the half-wave plate placed parallel between the two sub-transmission gratings.

4. An eight-channel pulse stretcher as described in claim 3, characterized in that, The parameters of the two transmission gratings are exactly the same.

5. An eight-channel pulse stretcher as described in claim 1, characterized in that, The distance between the concave mirror and the planar mirror is equal to the focal length of the concave mirror.

6. An eight-channel pulse stretcher as described in claim 1, characterized in that, The beam-shrinking unit includes a convex cylindrical mirror and a concave cylindrical mirror arranged in parallel.

7. An eight-channel pulse stretcher as described in claim 6, characterized in that, The convex cylindrical mirror and the concave cylindrical mirror are set to a common focal length.

8. An eight-channel pulse stretcher as described in claim 1, characterized in that, The polarization beam splitter is a polarization beam splitter flat plate or a polarization beam splitter prism.

9. An eight-channel pulse stretcher as described in claim 1, characterized in that, The collimator is an aspherical lens.

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