Compact single-shot ultrafast framing direct imaging device

Abstract

The present invention is applicable to the field of ultrafast optical imaging and provides a compact single-shot ultrafast framing direct imaging device, comprising: a femtosecond laser; a frequency multiplier; a beam splitter for splitting the frequency-doubled light and the remaining un-frequency-doubled fundamental light; a stretcher for pulse-stretching the fundamental light to obtain signal light; a temporal-spatial encoding system for splitting the signal light after irradiating an object into a two-dimensional array of equal-intensity sub-beams, and adding different time delays to each sub-beam in the array to obtain an illumination signal light array with different time delays that carries object information; a delayer for adjusting the delay of the pump light to synchronize the pump light with the illumination signal light array; and an optical parametric amplification imaging system for coupling the illumination signal light array with the delayed pump light to generate idler light carrying object information and record the image. This device achieves single-shot multi-frame imaging while maintaining high temporal and spatial resolution.

Description

Technical Field

[0001] The present invention belongs to the technical field of ultrafast optical imaging, and in particular relates to a compact single-shot ultrafast framing direct imaging device. Background Art

[0002] With the rapid development of ultrafast optical technology, the demand for high-temporal-resolution imaging of transient phenomena is increasing. Ultrafast framing imaging, an important method for capturing the dynamic evolution of transient events, is widely used in fields such as physics, chemistry, biomedicine, and materials science.

[0003] However, traditional ultrafast framing imaging technology often faces problems such as complex system, limited temporal resolution or insufficient sampling frames, and usually requires multiple repeated experiments to obtain information of multiple objects at different times, and cannot achieve single capture.

[0004] While existing ultrafast imaging technologies specifically designed for single-shot capture exist—capturing multiple images of an object at different moments in time with a single exposure (single shutter), these technologies have drawbacks. Based on the detection method, existing ultrafast imaging technologies for single-shot capture can be categorized as computational imaging and direct imaging. Computational imaging primarily achieves single-shot recording through optical encoding and computational decoding, while direct imaging eliminates the need for algorithms and instead directly captures the image onto the camera through optical means.

[0005] Direct imaging technology is more intuitive and reliable than computational imaging, but existing direct imaging technologies have problems such as low temporal resolution and complex systems. For example, the STAMP technology proposed by the University of Tokyo achieves femtosecond temporal resolution and multiple imaging through a complex optical system, but its device structure is complex, which limits its practical application. To solve this problem, they proposed a method based on diffraction optical element beam splitting and bandpass filtering to develop spectral filtering-time-sequential plenoptical photography (SF-STAMP), which greatly simplifies the system structure. However, this technology has difficulty in achieving high spatial resolution, and increasing the number of frames will lead to a decrease in the spatial resolution of each sub-image. Excessive sub-beams will also cause the light intensity of each channel to decrease, thus affecting the imaging quality.

[0006] Therefore, developing a single-shot ultrafast framing direct imaging device with high temporal and spatial resolution and high frame rate can not only effectively simplify the system structure, but also achieve multi-frame imaging while maintaining high temporal resolution. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a compact single-shot ultrafast framing direct imaging device, aiming to achieve single-shot multiple-frame imaging while maintaining high temporal and spatial resolution.

[0008] To solve the above technical problems, the present invention is implemented as follows: a compact single-shot ultrafast framing direct imaging device, comprising:

[0009] Femtosecond laser, used to generate femtosecond laser pulses;

[0010] a frequency multiplier for frequency-doubling the femtosecond laser pulse to obtain frequency-doubled light and remaining un-frequency-doubled fundamental frequency light, wherein the frequency-doubled light is used as pump light;

[0011] A light splitting component, used for performing light splitting processing on the frequency-doubled light and the fundamental frequency light;

[0012] A stretcher for stretching the fundamental frequency light pulse to obtain a signal light that can cover the entire ultrafast event time window; the signal light is used to illuminate the object to be imaged;

[0013] a temporal spatial coding system for dividing the signal light after irradiating the object into a two-dimensionally distributed array of equal-intensity sub-beams, and adding different time delays to each sub-beam in the array to obtain an array of illumination signal lights with different time delays that carry object information;

[0014] A delay device, used for adjusting the delay amount of the pump light so as to synchronize the pump light with the illumination signal light array;

[0015] The optical parametric amplification imaging system is used to couple the illumination signal light and the delayed pump light to generate idler light carrying object information and to record the idler light by imaging.

[0016] The compact single-shot ultrafast framing direct imaging device provided by the present invention can achieve single-shot multi-frame ultrafast imaging of transient processes. This is achieved by combining a temporal spatial coding system and an optical parametric amplification imaging system. The temporal spatial coding system can divide the signal light after irradiating the object into a two-dimensionally distributed array of equal-intensity sub-beams, and add different time delays to each sub-beam in the array to obtain an illumination signal light carrying object information. The various imaging parameter indicators are independent of each other. The imaging frequency depends on the time interval introduced by the temporal spatial coding system. The temporal resolution and spatial resolution depend on the pump pulse width and spatial bandwidth of the optical parametric amplification imaging system. The number of frames depends on the number of split beams in the temporal spatial coding system. Therefore, it has high imaging frequency, temporal resolution, spatial resolution and number of frames at the same time. In addition, the temporal spatial coding system has a simple and compact structure. This compact design not only reduces the complexity and cost of the system, improves the stability and reliability of the system, but also significantly increases the number of imaging frames, making it suitable for various scenarios such as laboratories and industrial sites. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1This is an optical structure diagram of the compact single-shot ultrafast framing direct imaging device provided by the present invention;

[0018] Figure 2 yes Figure 1 The optical structure diagram of the temporal coding system in FIG.

[0019] Figure 3 yes Figure 2 The structural principle diagram of the step mirror in FIG;

[0020] Figure 4A 、 Figure 4B yes Figure 3 Delay principle diagram of the mid-step mirror;

[0021] Figure 5 yes Figure 1 Optical structure diagram of the optical parametric amplification imaging system in . DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0023] See Figure 1 The compact single-shot ultrafast framing direct imaging device provided by the present invention includes a femtosecond laser 1, a frequency multiplier 2, a spectroscopic component 3, a stretcher 4, a temporal spatial coding system 5, a delay device 6, and an optical parametric amplification imaging system 7.

[0024] The femtosecond laser 1 is used to generate femtosecond laser pulses. As an example, a titanium sapphire femtosecond laser can be used to output femtosecond laser pulses with a pulse width of 25 fs, a pulse energy of 3.5 mJ, a central wavelength of 800 nm, and a corresponding spectral width of 60 nm.

[0025] The frequency multiplier 2 is used to frequency-double a portion of the femtosecond laser pulse to obtain frequency-doubled light and the remaining un-frequency-doubled fundamental frequency light. The material selection is not limited, for example, a 29.2° cutting angle and a thickness of 0.2 mm (barium metaborate) can be selected. -BBO crystal, the femtosecond laser pulse is incident on the crystal surface, obtaining 400nm doubled frequency light and unconverted 800nm ​​fundamental frequency light.

[0026] The beam splitting component 3 is used to split the frequency-doubled light and the fundamental frequency light. The frequency-doubled light is subsequently used as the pump light for the system. Specifically, a dichroic mirror can be used. The dichroic mirror has the function of splitting light of two different frequencies, reflecting the frequency-doubled light and transmitting the remaining undoubled fundamental frequency light.

[0027] Stretcher 4 is used to stretch the fundamental frequency light pulse to produce signal light that covers the ultrafast event time window; this signal light is used to illuminate the object to be imaged. Stretcher 4 can be a conventional pulse disperser, leveraging its dispersion properties to stretch the femtosecond laser pulse. For example, using the aforementioned 25 fs laser pulse as an example, it can be stretched into a chirped laser pulse with a central wavelength of 790 nm and a pulse width of 100 ps, ​​covering the ultrafast event time window. Of course, in practice, the femtosecond laser pulse can be stretched to any desired pulse width, depending on actual needs.

[0028] The temporal space coding system 5 is used to divide the signal light after irradiating the object into a two-dimensionally distributed array of equal-intensity sub-beams, and add different time delays to each sub-beam in the array to obtain an illumination signal light array with different time delays carrying object information.

[0029] Further references Figure 2 The temporal space coding system 5 may include a diffraction optical element 51 and a time delay array 52. ​​The diffraction optical element 51 is used to divide the signal light after irradiating the object into a two-dimensionally distributed sub-beam array with equal light intensity. The time delay array 52 is used to add different time delays to each sub-beam in the array to obtain an illumination signal light carrying object information.

[0030] The diffraction optical element 51 can be specifically a Dammann grating or a microlens array. The Dammann grating is a phase-type binary optical element that can efficiently convert the incident monochromatic light into an equidistant lattice with uniform light intensity in the far field of Fourier transform, avoiding the uneven light intensity distribution caused by single-hole diffraction in general gratings and having higher diffraction efficiency. For example, the amplitude transmittance function of the Dammann grating is It can be expanded into a Fourier series as

[0031] .

[0032] Where, represents the grating coefficient, is the Dirac function, d is the period of the grating, and is the two-dimensional coordinate on the grating plane, the amplitude transmittance function Describes the grating and Directional modulation of light.

[0033] Therefore, after passing through the Dammann grating, the light field is divided into An array of sub-beams of equal intensity. Taking the Dammann grating of 100 orders as an example, the signal light is divided into 49 sub-beams of equal intensity arranged in two-dimensional space after passing through the Dammann grating.

[0034] As an example, Figure 2 As shown, the time delay array 52 includes a first step mirror 521 and a second step mirror 522 placed in sequence. The first step mirror 521 is used to add a delay to each sub-beam in the array in a first direction, and the second step mirror 522 is used to add a delay to each sub-beam in the array in a second direction, wherein the first direction and the second direction are orthogonal, for example, the first direction is horizontal and the second direction is vertical, or the first direction is vertical and the second direction is horizontal.

[0035] Figure 3 The structure of the first and second stepped mirrors 521 and 522 is further illustrated. Both mirrors are composed of two glasses with different refractive indices, with the steps of the two glasses interlocking and forming a rectangular parallelepiped. The different materials of the two glasses are equivalent to different refractive indices, and each step has a different thickness. Due to the optical path difference, the sub-beams are delayed differently after passing through the different steps.

[0036] For example, see Figure 4A 、 Figure 4B , step mirror Ⅰ is composed of and Glass, Step Mirror II is made of and Glass composition. Group refractive index of glass n g2 is 1.50669, Group refractive index of glass n g1 is 1.50092, Group refractive index of glass n g3 is 1.54170, so the group refractive index difference of step mirror I is .

[0037] Similarly, the group refractive index difference of step mirror II can be obtained . Length of each step of step mirror I 4.036 mm, the length of each step of step mirror II The width between each step of the step mirror is 4.600 mm. is 3.7 mm. The time delay of step mirror I is obtained as =80fs, time delay of step mirror II ,in, c The speed of light.

[0038] Furthermore, the temporal spatial coding system 5 may also include: a first lens 53, located between the diffractive optical element 51 and the time delay array 52, for collimating the sub-beam array output by the diffractive optical element 51 and parallelizing the sub-beam array to be incident on the time delay array 52.

[0039] Furthermore, the temporal spatial coding system 5 may further include: a second lens 54 , located after the time delay array 52 , for focusing the illumination signal light onto the optical parametric amplification imaging system 7 .

[0040] Continue reading Figure 1 Delay 6 is used to adjust the delay of the pump light to synchronize it with the illumination signal light array. The temporal overlap of the picosecond signal photon pulse sequence is much greater than the pump light pulse width, making it easy to synchronize the pump light with each signal photon pulse.

[0041] The optical parametric amplification imaging system 7 is used to couple the illumination signal light array and the delayed pump light to generate idler light carrying object information and to record the idler light through imaging.

[0042] Figure 5 The structure of the optical parametric amplification imaging system 7 is further shown, including an optical parametric amplifier 71 , a filter 72 , a third lens 73 and a CCD camera 74 .

[0043] The optical parametric amplifier 71 is used to perform nonlinear optical parametric coupling amplification on the illumination signal light and the pump light. The amplified light beam includes the idler light carrying the object information, the illumination signal light and the pump light. The optical parametric crystal, the illumination signal light array and the pump light are incident on the surface of the optical parametric crystal in a collinear matching manner, and 49 idler photon beams with a central wavelength of 810nm are generated through optical parametric conversion.

[0044] The filter 72 is located after the optical parametric amplifier 71 and is used to filter the light beam coupled and amplified by the optical parametric amplifier 71, allowing only the idler light to pass through. After filtering, the idler photon beam is separated from the illumination signal light and the pump light.

[0045] The third lens 73 is used to form an image of the idler light passing through the filter 72 .

[0046] The CCD camera 74 is used to record the image formed by the third lens 73 .

[0047] Because each signal photon beam has a different time delay, after optical parametric amplification, the pump light acts as a short shutter, sampling individual idler photon beams that carry information about the object at different moments. Therefore, a single exposure can capture information about a transient event at 49 different moments on a CCD camera 74.

[0048] It should also be noted that if some reflective or refracting elements are added to the device only to change the direction of light transmission, it still falls within the scope of this patent. Figure 1 In the single-shot ultrafast framing direct imaging device, the device further includes a reflector 8 located on the reflection light path of the dichroic mirror, for reflecting the frequency-doubled light to the retarder 6 .

[0049] In summary, the compact single-shot ultrafast framing direct imaging device provided by the present invention has the following advantages:

[0050] 1. This is achieved by combining a temporal spatial coding system with an optical parametric amplification (OPA) imaging system. The temporal spatial coding system splits the signal light after illuminating the object into a two-dimensional array of equal-intensity sub-beams. Different time delays are added to each sub-beam in the array to produce illumination signal light that carries object information. The imaging parameters are independent of each other: the imaging frequency is determined by the time interval introduced by the temporal spatial coding system, the temporal and spatial resolutions are determined by the pump pulse width and spatial bandwidth of the OPA imaging system, and the number of frames is determined by the number of split beams in the temporal spatial coding system. This achieves high imaging frequency, temporal resolution, spatial resolution, and number of frames simultaneously.

[0051] 2. Through the temporal spatial coding system, this compact design not only reduces system complexity and cost, improves system stability and reliability, but also significantly increases the number of imaging frames, making it suitable for a variety of scenarios such as laboratories and industrial sites.

[0052] 3. The introduction of nonlinear optical parametric amplification technology also provides high gain and wavelength conversion capabilities for imaging systems. High gain significantly amplifies weak light signals, resulting in high system sensitivity. Wavelength conversion expands the detection wavelength of imaging to the mid-infrared and other wavelengths, meeting the different imaging wavelength requirements of different application scenarios.

[0053] 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 and improvements 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 compact single-shot ultrafast framing direct imaging device, characterized in that: include: Femtosecond laser, used to generate femtosecond laser pulses; A frequency multiplier for frequency-doubling the femtosecond laser pulse to obtain frequency-doubled light and remaining un-frequency-doubled fundamental frequency light, wherein the frequency-doubled light is used as pump light; A light splitting component, used for performing light splitting processing on the frequency-doubled light and the fundamental frequency light; A stretcher for stretching the fundamental frequency light pulse to obtain a signal light that can cover the entire ultrafast event time window; the signal light is used to illuminate the object to be imaged; A temporal spatial encoding system includes a diffractive optical element and a time delay array. The diffractive optical element is used to split the signal light after irradiating the object into a two-dimensional array of equal-intensity sub-beams. The time delay array is used to add different time delays to each sub-beam in the equal-intensity sub-beam array to obtain an array of illumination signal light with different time delays that carries object information. A delay device, used for adjusting the delay amount of the pump light so as to synchronize the pump light with the illumination signal light array; An optical parametric amplification imaging system includes an optical parametric amplifier, a filter, a third lens, and a CCD camera; the optical parametric amplifier is used to perform nonlinear optical parametric coupling amplification on the illumination signal light and the pump light, and the amplified light beam includes idler light carrying object information; the filter is located after the optical parametric amplifier and is used to filter the light beam amplified by the optical parametric amplifier, allowing only the idler light to pass; the third lens is used to image the idler light; and the CCD camera is used to record the image formed by the third lens.

2. The single-shot ultrafast framing direct imaging device according to claim 1, wherein: The light splitting component is a dichroic mirror, which is used to reflect the frequency-doubled light and transmit the remaining un-frequency-doubled fundamental frequency light.

3. The single-shot ultrafast framing direct imaging device according to claim 2, wherein: The single-shot ultrafast framing direct imaging device further comprises: A reflecting mirror is located on the reflecting light path of the dichroic mirror and is used to transmit the frequency-doubled light to the retarder.

4. The single-shot ultrafast framing direct imaging device according to claim 1, wherein: The diffractive optical element is a Dammann grating.

5. The single-shot ultrafast framing direct imaging device according to claim 1, wherein: The time delay array comprises a first step mirror and a second step mirror placed in sequence; The first stepped mirror is used to add a delay to each sub-beam in the array of equal-intensity sub-beams in a first direction, and the second stepped mirror is used to add a delay to each sub-beam in the array of equal-intensity sub-beams in a second direction; The first direction and the second direction are orthogonal.

6. The single-shot ultrafast framing direct imaging device according to claim 5, wherein: The first stepped mirror and the second stepped mirror are both made of glass with two different refractive indices, and the steps of the two glasses are interlocked with each other and are arranged in a rectangular parallelepiped shape as a whole.

7. The single-shot ultrafast framing direct imaging device according to claim 1, wherein: The temporal space coding system further includes: The first lens is located between the diffractive optical element and the time delay array, and is used for collimating the sub-beam array output by the diffractive optical element and then parallelizing the sub-beam array to be incident on the time delay array.

8. The single-shot ultrafast framing direct imaging device according to claim 1, wherein: The temporal space coding system further includes: The second lens is located after the time delay array and is used to focus the illumination signal light onto the optical parametric amplification imaging system.

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