Arbitrary temporal waveform light pulse generation device

Abstract

An arbitrary time waveform light pulse generating device, comprising a short pulse light source, a light splitting element, a collimation and expansion system, a first imaging system, a grating, a second imaging system, a spatial shaping element, a coupling lens and a single mode optical fiber; after the short pulse light passes through the light splitting element, the reflected light acts as a short pulse seed source, the transmitted light is fully irradiated to the effective light transmission area of the grating after collimation and expansion, and the phase wave front of the reflected light pulse is tilted at a certain angle compared with the intensity wave front. The spatial shaping element in the later stage is in a precise object-image relationship with the grating, when the spatial shaping element combines with the later stage coupling system to form a preset spatial transmittance distribution, the phase wave front of the light pulse is also modulated by the corresponding spatial transmittance, after the influence of space-time distortion and the like is eliminated through the later stage coupling system, the time waveform of the coupled output light pulse has a linear corresponding relationship with the preset spatial transmittance distribution, and the short pulse light reflected by the light splitting element belongs to the same source relationship. The present application not only realizes absolute homology of long and short pulses, but also has the advantages of high time resolution, wide time width range, simple optical structure and independence from electronic chips and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of time waveform control of optical pulse, and particularly relates to an arbitrary time waveform optical pulse generating device. BACKGROUND

[0002] In the field of inertial confinement fusion, by precisely regulating the time waveform of laser converging on a target pellet, the interaction process between laser and matter can be precisely controlled, thereby directly affecting the fusion process and the fusion efficiency. Therefore, the precise control technology of laser pulse time waveform is of great significance for improving the efficiency of inertial confinement fusion.

[0003] For the precise regulation of laser time pulse, there are mainly two aspects of requirements: on the one hand, multiple optical pulses need to be precisely synchronized to achieve synchronous arrival at the target pellet, and when the long and short optical pulses of different paths are not homologous, it is difficult to achieve absolute zero synchronization; on the other hand, the time waveform of each path of optical pulse needs to be precisely adjustable, and the resolution needs to be better than one percent of the total time width. Although the AWG technology combined with electro-optical modulator can generate arbitrary shaping optical pulses with a time width of several nanoseconds, when the required time width of optical pulse is about hundreds of picoseconds, the time resolution requirement reaches picosecond level, and the electronic method cannot generate arbitrary shaping optical pulses with such high time resolution due to the bandwidth limitation of electronic elements.

[0004] Although the time resolution accuracy can be improved by time-frequency conversion and other optical technologies, there are problems such as complex optical path and difficult extension of time width. SUMMARY

[0005] The application aims to overcome the problems of the current arbitrary optical pulse generation technology, such as the inability to achieve zero synchronization accuracy and the inability to achieve picosecond level of pulse time resolution, and provides an arbitrary time waveform optical pulse generation device, so that the reflected light of the short pulse light after passing through the light splitting element is used as a short pulse seed source, the transmitted light passes through the collimation and expansion system and fully irradiates the effective light transmission area of the grating, and the phase wavefront of the reflected light pulse has a certain angle of inclination compared with the intensity wavefront. The spatial shaping element in the later stage has an accurate object and image relationship with the grating, when the spatial shaping element combines with the later stage coupling system to form a preset spatial transmittance distribution, the phase wavefront of the optical pulse is also modulated by the corresponding spatial transmittance, and after the influence of the space-time distortion is eliminated by the later stage coupling system, the time waveform of the coupled output optical pulse has a linear corresponding relationship with the preset spatial transmittance distribution. Therefore, by designing appropriate optical system parameters and the transmittance distribution of the spatial shaping element, the device can output optical pulses with a preset time waveform, and the short pulse light reflected by the light splitting element belongs to the same source relationship, and the absolute homology of long and short pulses is realized. Compared with the current arbitrary optical pulse generation technology, the optical pulse has the advantages of high synchronization accuracy, high time resolution, wide time width range (hundred picoseconds to nanosecond level), simple optical structure and independence from electronic chips.

[0006] The technical solution of the application is as follows:

[0007] An arbitrary time waveform optical pulse generation device, comprising a short pulse light source, characterized in that: a light splitting element, a collimation and expansion system, a first imaging system, a grating, a second imaging system, a spatial shaping element, a coupling lens and a single mode optical fiber are sequentially arranged along the transmission direction of the short pulse light source.

[0008] The short pulse light output by the short pulse light source is reflected by the light splitting element, the reflected light is used as a short pulse seed source, and the transmitted light sequentially passes through the collimation and expansion system and the first imaging system, and is incident on the grating at an angle θ g The effective light transmission area of the grating is irradiated, so that the phase wavefront of the diffracted light pulse reflected by the grating is inclined compared with the intensity wavefront, and the diffracted light passes through the second imaging system at an angle θ SLM The spatial shaping element is irradiated, so that the spatial shaping element has an accurate object and image relationship with the grating, the spatial shaping element is loaded with a transmittance or phase distribution, so that the distribution of the spot coverage area in the modulation dimension has a linear corresponding relationship with the spatial transmittance distribution.

[0009] Further, the time width t in Close to the short pulse limit of Fourier transform.

[0010] Further, the short pulse light output by the short pulse light source is irradiated on the grating with a certain incident angle and a certain spot size after sequentially passing through the light splitting element, the collimating and expanding system and the first imaging system, and the spot size is as close as possible to the effective light passing area of the grating.

[0011] Further, the short pulse light output by the short pulse light source is irradiated on the grating with a certain incident angle and a certain spot size after sequentially passing through the light splitting element, the collimating and expanding system and the first imaging system, and the spot size is as close as possible to the effective light passing area of the grating.

[0012] Further, the short pulse light output by the short pulse light source is irradiated on the grating with a certain incident angle and a certain spot size after sequentially passing through the light splitting element, the collimating and expanding system and the first imaging system, and the spot size is as close as possible to the effective light passing area of the grating.

[0013] Further, the spatial shaping element is inclined at a certain angle, and the inclination angle satisfies the object-image relationship of the second imaging system.

[0014] Further, the coupling lens is an aberration-corrected lens, so that the converging spot size is close to the diffraction limit size.

[0015] Further, the numerical aperture of the single-mode optical fiber is greater than the numerical aperture of the converging light beam of the coupling lens.

[0016] Further, the incident angle θ SLM of the spatial shaping element and the incident angle θ g of the grating satisfy the relationship: tan(θ SLM ) = M2 tan(θ g ), wherein M2 is the magnification of the second imaging system.

[0017] Compared with the prior art, the present application has the following beneficial effects:

[0018] By utilizing the time-space coupling characteristics of the laser pulse, the linear corresponding relationship between the time waveform of the pulse and the spatial transmittance distribution of the spatial shaping element is realized through the optical system design, so that the long pulse light time waveform is high-precision and arbitrary shaped, and the long and short pulses are absolutely homologous.

[0019] By utilizing the characteristics that the phase wavefront and the intensity wavefront of the reflected light pulse exist at a certain inclination angle, and combining the image transfer and the time-space coupling characteristics of the inclined pulse wavefront, the transmittance distribution of the spatial shaping element is regulated to realize the accurate regulation of the pulse time waveform.

[0020] By designing suitable optical system parameters and the transmittance distribution of the spatial shaping element, the device can output laser pulses with preset time waveforms.

[0021] Compared with the existing time pulse generation technology, the device has the advantages of high synchronization accuracy, high time resolution, wide time width range (hundred picoseconds to nanosecond level), simple optical structure and independence from electronic chips. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is a structural schematic diagram of the arbitrary time waveform optical pulse generation device with zero synchronization accuracy of the present application.

[0023] Figure 2 is a structural schematic diagram of the collimation and beam expansion system in the embodiment of the present application.

[0024] Figure 3 is a structural schematic diagram of the first imaging system in the embodiment of the present application.

[0025] Figure 4 is a structural schematic diagram of the second imaging system in the embodiment of the present application. DETAILED DESCRIPTION

[0026] The present application will be further described below in conjunction with the embodiments and the drawings, but the protection scope of the present application should not be limited thereby.

[0027] First, refer to Figure 1 , Figure 1 is a structural schematic diagram of the arbitrary time waveform optical pulse generation device with zero synchronization accuracy of the present application, and from the diagram, it can be seen that the arbitrary time waveform optical pulse generation device comprises a short pulse light source 1, further comprises a light splitting element 1a arranged in sequence along the transmission direction of the short pulse light source, a collimation and beam expansion system 2, a first imaging system 3, a grating 4, a second imaging system 5, a spatial shaping element 6, a coupling lens 7 and a single-mode optical fiber 8. The short pulse light output by the short pulse light source sequentially passes through the light splitting element, the collimation and beam expansion system and the first imaging system, and then irradiates the effective light transmission area of the grating at an incident angle θ g , so that the phase wavefront and the intensity wavefront of the diffracted light pulse reflected after the grating are tilted, and the diffracted light passes through the second imaging system at an incident angle θ SLM irradiates the spatial shaping element, so that the spatial shaping element and the grating form an accurate object, image relationship, and the spatial shaping element is loaded with a transmittance or phase distribution, so that the distribution of the spot coverage area in the modulation dimension has a linear correspondence relationship with the spatial transmittance distribution.

[0028] The short pulse light source 1 can be a solid or fiber laser with output pulse time of femtosecond, picosecond or nanosecond width. The beam splitting element 1a is generally a beam splitting cube in the embodiment, and the reflection / transmission ratio is set according to the energy requirement of the subsequent light path. The collimation and expansion system 2 is composed of a pair of concave and convex lenses, the virtual focal point of the concave lens and the real focal point of the convex lens coincide at position F, and the focal lengths of the two are f1 and f2 respectively, and the expansion ratio of the system is f2 / f1 as shown in Figure 2 The first imaging system 3 is composed of a pair of convex lenses as the imaging transfer structure, and the focal lengths of the two lenses are f3 and f4 respectively, and they are apart by f3+f4 to ensure that the back focal point of the front lens and the front focal point of the rear lens coincide with each other, and the magnification of the imaging system is f4 / f3 as shown in Figure 3 The grating 4 is a reflective grating, and the reflective film layer material can be aluminum film, gold film or dielectric film material, etc. The second imaging system 5 is composed of a pair of convex lenses as the imaging transfer structure, and the focal lengths of the two lenses are f5 and f6 respectively, and they are apart by f5+f6 to ensure that the back focal point of the front lens and the front focal point of the rear lens coincide with each other, and the magnification of the imaging system is f6 / f5 as shown in Figure 4 The spatial shaping element 6 can be a transmissive amplitude type spatial light modulator, a transmissive phase type spatial light modulator, a reflective amplitude type spatial light modulator or a reflective phase type spatial light modulator, and the applicable wavelength matches the incident light wavelength. The coupling lens 7 is a cemented type of anastigmatic lens or an aspherical lens, and the applicable wavelength matches the incident light wavelength. The single mode optical fiber 8 is a single mode optical fiber with no inclination angle at the end face, the aperture size of the optical fiber is ≥ the spot size after the light converging through the coupling lens, and the numerical aperture of the optical fiber is ≥ the numerical aperture of the converging light beam of the coupling lens.

[0029] The operation method of the present application:

[0030] The output light wavelength of the short pulse light source is λ, the beam waist radius is w0, the time width is τ0, the expansion ratio of the collimation and expansion system is M0, the magnification of the first imaging system is M 1， The magnification of the second imaging system is M2, the grating density is Λ, and the diffraction angle after the grating reflection is θ. The design and adjustment are carried out according to the following steps:

[0031] (1) When the output pulse time width is required to be 2τ, and the pulse intensity is I(t) (t≤2τ) with time distribution, the relationship τ=w0·M0·M1·λ / (c·Λ·cos(θ)) must be met, and the parameters M0, M1, M2, Λ and θ are configured according to the formula, where c=3×10 8 m / s.

[0032] (2) Adjust the angle of the spatial shaping element to make it and the grating form object and image relationship, and the incident angle of the spatial shaping element is θ SLMThe incident angle θ of the grating g satisfies the relationship: tan(θ SLM )=M2·tan(θ g ).

[0033] (3) Adjust the transmittance or phase distribution loaded on the spatial shaping element, so that the distribution of the spot coverage area in the modulation dimension linearly corresponds to the I(t) distribution.

[0034] (4) Precisely fine-tune the single-mode optical fiber in each dimension such as up and down, left and right, and tilt angle, so that the output waveform approaches the preset state.

[0035] Example 1

[0036] The short pulse light source 1 outputs light with a wavelength of 1053 nm, a beam waist radius of w0=2 mm, and a time width of τ0≤1 ps. The expansion ratio of the collimation and expansion system 2 is M0=3.5, and the magnification of the first imaging system 3 is M1=7 ， The magnification of the second imaging system 5 is M2=4 / 21, the density of the grating 4 is Λ=1800 l / mm, and the diffraction angle after reflection of the grating is θ=71.4 degrees. Thus, the time width of the output pulse of the device is 2τ=970 ps.

[0037] The focal length of the concave lens in the collimation and expansion system 2 is -10 mm, and the focal length of the convex lens is 35 mm.

[0038] The focal lengths of the two lenses in the first imaging system 3 are 50 mm and 350 mm, respectively.

[0039] The grating 4 uses a reflective gold film grating with a line density Λ=1800 l / mm and an effective area ≥100 mm×100 mm.

[0040] The focal lengths of the two lenses in the second imaging system 5 are 40 mm and 210 mm, respectively.

[0041] The spatial shaping element 6 uses an amplitude-type LCOS spatial light modulator, such as the HDSLM80RA of Raytheon Company, with a resolution of 1920*1200 and a unit pixel size of 8 microns. The transmittance distribution loaded on the device linearly corresponds to the time intensity distribution of the pulse in the one-dimensional direction of the reflection normal.

[0042] The focal length of the coupling lens is 10 cm, and the core diameter of the single-mode optical fiber is 10 um.

[0043] Example 2

[0044] The difference from the embodiment 1 is that the beam waist radius of the short pulse light source 1 is w0=10mm, the time width is τ0≤50ps, the magnification of the second imaging system 5 is M2=4 / 105, and when other optical system or element parameters are unchanged, the effective area of the grating 4 must satisfy ≥500mm×500mm. At this time, the spatial shaping element 6 still uses the same device model as the embodiment 1.

[0045] Under this condition, the time width of the pulse output by the device reaches 2τ=4.85ns.

[0046] When the transmittance distribution loaded on the spatial shaping element 6 is linearly corresponding to the time intensity distribution of the pulse in the one-dimensional direction of the reflection normal, the device outputs the required light pulse with a specific time waveform.

Claims

1. An arbitrary temporal waveform optical pulse generating apparatus comprising a short pulse light source, characterized by: The short-pulse light source is sequentially provided with a light splitting element, a collimating and expanding system, a first imaging system, a grating, a second imaging system, a spatial shaping element, a coupling lens and a single-mode optical fiber in sequence along the transmission direction of the short-pulse light source. The short pulse light output by the short pulse light source is reflected by the light splitting element, the reflected light is used as a short pulse seed source, and the transmitted light sequentially passes through the collimation and expansion system and the first imaging system to enter the second imaging system at an incident angle θ g An effective light passing area of the grating is irradiated, so that the phase wave front and the intensity wave front of the diffracted light pulse reflected by the grating are tilted, and the diffracted light sequentially passes through the second imaging system to enter the third imaging system at an incident angle θ SLM The spatial shaping element is irradiated, so that the spatial shaping element and the grating are in an accurate object-image relationship, the spatial shaping element is loaded with a transmittance or phase distribution, and the distribution of the spot coverage area in the modulation dimension has a linear correspondence relationship with the spatial transmittance distribution.

2. The arbitrary temporal waveform optical pulse generating apparatus according to claim 1, wherein: The time width t of the short pulse light source in Approach to the short pulse limit of the Fourier transform.

3. The arbitrary temporal waveform optical pulse generating apparatus according to claim 1, wherein: The short-pulse light output by the short-pulse light source is sequentially irradiated on the grating through the light splitting element, the collimating and expanding system and the first imaging system at a certain incident angle, and the incident angle satisfies the grating equation.

4. The arbitrary temporal waveform optical pulse generating apparatus according to claim 1, wherein: The short-pulse light output by the short-pulse light source is sequentially irradiated on the grating through the light splitting element, the collimating and expanding system and the first imaging system at a certain incident angle and a certain spot size, and the spot size is as close as possible to the effective light transmission area of the grating.

5. The arbitrary temporal waveform optical pulse generating apparatus according to claim 1, wherein: The short-pulse light output by the short-pulse light source is sequentially irradiated on the spatial shaping element through the light splitting element, the collimating and expanding system, the first imaging system, the grating and the second imaging system, and the spot size is as close as possible to the effective working area of the spatial shaping element.

6. The arbitrary temporal waveform optical pulse generating apparatus according to claim 1, wherein: The spatial shaping element is inclined at a certain angle, and the inclined angle satisfies the object-image relationship of the second imaging system.

7. The arbitrary temporal waveform optical pulse generating apparatus according to claim 1, wherein: The coupling lens is an aberration-corrected lens, and the converging spot size is close to the diffraction limit size.

8. The arbitrary temporal waveform optical pulse generating apparatus according to claim 1, wherein: The numerical aperture of the single-mode optical fiber is greater than the numerical aperture of the converging light beam of the coupling lens.

9. The arbitrary temporal waveform optical pulse generating apparatus according to any one of claims 1 to 8, wherein: The incidence angle θ of the spatial shaping element SLM The incidence angle θ of the grating g The relationship tan(θ SLM ) = M2 tan(θ g ) is satisfied, where M2 is the magnification of the second imaging system.

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