Low-time dispersion reflection type optical system and ultrafast imaging streak camera

Abstract

The invention relates to a low time dispersion reflection type optical system and an ultrafast imaging streak camera, which are mainly used for solving the problems that an optical path difference about picosecond is introduced in a visible light spectrum range under the condition that a transmission type optical input lens is provided with a wide spectrum light source, so that the imaging quality and time resolution are influenced; and the technical problem that the streak camera in the existing synchrotron radiation light source device is difficult to measure the length of the electron beam bunch under the condition of low current intensity is solved. In the low-time-dispersion reflective optical system, a primary mirror, a third mirror and a secondary mirror form an off-axis three-mirror structure, a front mirror is arranged at the incident end of the off-axis three-mirror structure, a rear mirror is arranged at the emergent end of the off-axis three-mirror structure, and reflectors are adopted, so that time dispersion is effectively reduced; and only 2fs optical path difference is introduced for a light source in a visible light band spectral range, so that the optical lens has the characteristic of small time dispersion, and has remarkable advantages compared with the time dispersion of a traditional transmission-type optical lens in a visible light band picosecond order.

Description

Technical Field

[0001] The present invention relates to an optical system and a streak camera, and in particular to a low-time-dispersion reflective optical system and an ultrafast imaging streak camera. Background Art

[0002] A streak camera is an ultrafast diagnostic scientific instrument with both high temporal and spatial resolution, used to record changes in optical signals over extremely short periods of time. Its operating principle is that a light signal is projected onto a photocathode, where it is converted into photoelectron pulses carrying temporal information. These photoelectron pulses then enter a deflection system, where electrons arriving at different times are deflected to different positions. These electrons then strike a fluorescent screen, forming streaks of light that record the temporal changes in the light signal. The streak converter tube, the core component of the streak camera, controls the deflection of the electron signal and determines the camera's ultimate temporal and spatial resolution. To achieve ultrafast imaging using the streak converter tube, a low-light-level imaging system consisting of an image intensifier and a CCD readout camera must be installed on the fluorescent screen behind the streak converter tube. Furthermore, a suitable optical input lens must be designed for the streak converter tube to transmit the image of the optical slit to the streak converter tube's photocathode.

[0003] In the prior art, streak image converters usually use a transmissive optical input lens. When the incident light is a quasi-monochromatic laser (i.e., narrow spectrum light), for example, streak cameras are used in the field of laser ultrafast diagnosis (such as inertial confinement fusion, material fluorescence lifetime measurement), a quasi-monochromatic incident laser is usually used to interact with the object to be measured. The quasi-monochromatic incident laser has good monochromaticity, so the time dispersion caused by the transmissive optical input lens can generally be ignored. In the case where the incident light is a synchrotron radiation light source, such as in an accelerator device using a synchrotron radiation light source, the spectral range of the synchrotron radiation light source is relatively wide, mainly in the visible light band. The dispersion effect caused by the chromatic aberration of light of different wavelengths will cause the transmissive optical input lens to introduce time dispersion, affecting the imaging quality.

[0004] Therefore, for imaging with broad-spectrum light sources, the transmissive optical input lens will introduce an optical path difference of about picoseconds in the visible light spectrum range, i.e., temporal dispersion, which affects the imaging quality and temporal resolution.

[0005] The normal operating mode of a synchrotron radiation light source is the operation of multiple electron bunches. The longitudinal coupling impedance of the storage ring reflects the impedance characteristics of the storage ring. By observing the stretching effect of the electron bunch length, the longitudinal coupling impedance of the storage ring can be estimated.

[0006] In high-current optical systems, in order to solve the problem of dispersion effect caused by chromatic aberration of light of different wavelengths, a bandpass filter can be used to select light of a certain wavelength band when measuring the length of the electron bunch.

[0007] In optical systems with low current intensities, due to the weak intensity of the synchrotron radiation, the number of photoelectron pulses is insufficient or cannot be detected, which may lead to problems such as blurred or distorted fringes, increased noise, and limited dynamic range, affecting the imaging quality and measurement accuracy, making it impossible to obtain accurate beam parameters. Therefore, in the prior art, the method of expanding the spectral range of the measured light is usually adopted to increase the intensity of the measured light, making the image captured by the streak camera clearer and improving the signal-to-noise ratio of the measurement results. However, expanding the spectral range of the measured light cannot be used with filters, so the method of measuring the length of electron bunches in optical systems with high current intensities is no longer applicable to optical systems with low current intensities. Therefore, it is difficult for streak cameras in synchrotron radiation light source devices to measure the length of electron bunches under low current intensities. Summary of the Invention

[0008] The purpose of the present invention is to solve the technical problems that a transmissive optical input lens will introduce an optical path difference of about picoseconds in the visible light spectrum range in the case of a wide-spectrum light source, affecting the imaging quality and time resolution, and that the streak camera in the existing synchrotron radiation light source device has difficulty in measuring the length of the electron bunch under low current intensity conditions. The present invention proposes a low-time dispersion reflective optical system and an ultrafast imaging streak camera.

[0009] To solve the above technical problems, the present invention provides the following technical solutions:

[0010] A low temporal dispersion reflective optical system, which is special in that:

[0011] Including front reflector, primary mirror, tertiary mirror, secondary mirror and rear reflector;

[0012] The front reflector and the rear reflector are both plane reflectors, and the center points of the front reflector and the rear reflector are located on the same straight line, the angle between the front reflector and the straight line is 45°, and the angle between the rear reflector and the straight line is -45°;

[0013] The front reflector is used to reflect the incident light from the object side to form the first reflected light;

[0014] The primary mirror and the three mirrors share a same spherical concave reflector, and the central axis of the spherical concave reflector is perpendicular to the line connecting the center points of the front reflector and the rear reflector;

[0015] The primary mirror is arranged on the optical path of the first reflected light, and is used to reflect the first reflected light into the second reflected light;

[0016] The secondary mirror is a spherical convex reflector, which serves as an aperture stop of the optical system; the secondary mirror is coaxially arranged with the spherical concave reflector, and is used to reflect the second reflected light into the third reflected light;

[0017] The three mirrors are arranged on the optical path of the third reflected light, and are used to reflect the third reflected light into the fourth reflected light;

[0018] The rear reflecting mirror is used to reflect the fourth reflected light to the image side.

[0019] Furthermore, the primary mirror and the third mirror are rotationally symmetric about the central axis of the secondary mirror;

[0020] The front reflector and the rear reflector are rotationally symmetric about the central axis of the secondary mirror.

[0021] Furthermore, the air thickness between the center point of the front reflector and the center point of the object space is 50 mm;

[0022] The air thickness between the center point of the front reflector and the center point of the main mirror is 150 mm;

[0023] The air thickness between the center point of the third mirror and the center point of the secondary mirror is 98.04 mm;

[0024] The center point of the primary mirror is the intersection of the first reflected light reflected by the center point of the front reflector and the primary mirror;

[0025] The center point of the secondary mirror is the intersection point of the second reflected light reflected by the center point of the primary mirror and the secondary mirror;

[0026] The center point of the three mirrors is the intersection of the third reflected light reflected by the center point of the secondary mirror and the three mirrors.

[0027] Furthermore, the curvature radius of the spherical concave reflector is -200 mm;

[0028] The curvature radius of the secondary mirror is 100 mm.

[0029] Furthermore, the front reflector is circular with a radius of 23.4 mm;

[0030] The radius of the circumference of the outer edge of the secondary mirror is 5.6 mm;

[0031] The rear reflector is circular with a radius of 24.2 mm.

[0032] Furthermore, the thickness of air between the center point of the front reflector and the center point of the object space is 50 mm;

[0033] The thickness of air between the center point of the rear reflector and the center point of the image side is 53.717 mm.

[0034] Furthermore, the front reflector and the rear reflector are metal film reflectors.

[0035] The present invention also provides an ultrafast imaging streak camera, which is special in that it adopts the above-mentioned low-time-dispersion reflective optical system as an optical input lens.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] 1. The present invention provides a low-temporal-dispersion reflective optical system, in which a primary mirror, a third mirror, and a secondary mirror form an off-axis three-mirror structure. The front reflector is arranged at the incident end of the off-axis three-mirror structure, and the rear reflector is arranged at the exit end of the off-axis three-mirror structure. The optical lenses in the optical system are all reflectors, which effectively reduces temporal dispersion. For light sources in the visible light spectrum range, only an optical path difference of 2 fs is introduced, making it have the characteristic of low temporal dispersion. Compared with traditional transmissive optical lenses with picosecond temporal dispersion in the visible light band, this system has significant advantages.

[0038] 2. The present invention provides a low-temporal-dispersion reflective optical system. The air thickness between the center of the front reflector and the center of the object space is 50 mm, and the air thickness between the center of the front reflector and the center of the spherical concave reflector is 150 mm. This results in an optical system length of 160 mm, a height of 170 mm, a numerical aperture of 0.05, and a distortion of ≤0.08%. This system features a compact structure, high spatial resolution, minimal distortion, and simultaneous wide imaging bandwidth, making it suitable for picosecond wide-band ultrafast imaging and sub-picosecond monochrome ultrafast imaging streak cameras.

[0039] 3. The present invention provides a low-temporal-dispersion reflective optical system in which the primary and three mirrors are symmetrical about the secondary mirror, and the front and rear reflectors are symmetrical about the secondary mirror. This symmetrical arrangement effectively eliminates first-order aberrations, reduces the Seidel coefficient, and allows aberrations along symmetrical light paths to cancel each other out, thereby improving the system's imaging quality.

[0040] 4. The present invention provides an ultrafast imaging streak camera that uses a low-temporal-dispersion reflective optical system as its optical input lens. Since the optical system has low temporal dispersion and no dispersion effect on light of different wavelengths, this makes it possible to use the streak camera to measure the length of electron bunches under low current intensity conditions in a synchrotron radiation light source device. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 A three-dimensional layout diagram of an embodiment of a low temporal dispersion reflective optical system according to the present invention;

[0042] Figure 2 An optical transfer function (OTF) diagram of an embodiment of a low temporal dispersion reflective optical system according to the present invention;

[0043] Figure 3A spot diagram of an embodiment of a low temporal dispersion reflective optical system according to the present invention;

[0044] Figure 4 This is a grid distortion diagram of an embodiment of a low temporal dispersion reflective optical system of the present invention, wherein the distortion of the system is ≤0.08%;

[0045] Figure 5 This is a graph showing the temporal dispersion results of an embodiment of a low temporal dispersion reflective optical system according to the present invention, approximately 2 fs.

[0046] Description of reference numerals:

[0047] 1. Object side; 2. Front reflector; 31. Primary mirror; 32. Tertiary mirror; 4. Secondary mirror; 5. Rear reflector; 6. Image side. DETAILED DESCRIPTION

[0048] The present invention will be further described below with reference to the accompanying drawings and examples.

[0049] The present invention provides a low time dispersion reflective optical system, such as Figure 1 As shown, it includes a front reflector 2, a primary mirror 31, a third mirror 32, a secondary mirror 4 and a rear reflector 5.

[0050] The front reflector 2 is a circular plane reflector, which is arranged in the incident path of the light. The front reflector 2 and the rear reflector 5 are both plane reflectors. The center points of the front reflector 2 and the rear reflector 5 are located on the same straight line. The angle between the front reflector 2 and the straight line is 45 degrees, and the angle between the rear reflector 5 and the straight line is -45 degrees.

[0051] Front reflector 2 redirects the optical path and improves the compactness of the structure. It reflects incident light from object 1, forming first reflected light. Object 1 is typically used to describe a side or space associated with an object in an optical system. In this embodiment, object 1 is a circular surface with a diameter of 30 mm.

[0052] The primary mirror 31 and the third mirror 32 are arranged rotationally symmetrically with respect to the secondary mirror 4, and therefore share the same spherical concave reflector. The primary mirror 31 is arranged on the optical path of the first reflected light and is used to reflect the first reflected light into the second reflected light;

[0053] The secondary mirror 4 is a spherical convex reflector, which serves as an aperture stop of the optical system. The secondary mirror 4 is arranged on the optical path of the second reflected light and is coaxial with the spherical concave reflector to reflect the second reflected light into the third reflected light.

[0054] The third mirror 32 is arranged on the optical path of the third reflected light, and is used to reflect the third reflected light into the fourth reflected light; the primary mirror 31, the secondary mirror 4 and the third mirror 32 constitute an off-axis three-mirror structure.

[0055] The rear reflector 5 is used to reflect the fourth reflected light to the image side 6. In this embodiment, the image side 6 is a circular imaging surface with a diameter of 30 mm.

[0056] The front and rear mirrors 2 and 5 are rotationally symmetrical about the secondary mirror 4. They are used to adjust the optical path so that the object space 1 and the image space 6 are coaxial. They are made of metal-coated mirrors, such as gold, silver, or aluminum, which are highly reflective in the visible light band. For imaging in other wavelengths, such as the deep ultraviolet or mid-infrared, high-reflectivity mirrors tailored for these wavelengths can also be used.

[0057] The parameters of the front reflector 2 , the primary mirror 31 , the third mirror 32 , the secondary mirror 4 and the rear reflector 5 are shown in Table 1.

[0058] Table 1

[0059] Face type Radius of curvature radius Air thickness type Tilt angle Monogatari 15mm 50mm Front reflector Standard plane infinity 23.4mm 150mm reflector 45° primary mirror Standard sphere -200mm 52.1mm 98.04mm reflector secondary mirror Standard sphere -100mm 5.6mm 98.04mm reflector Three mirrors Standard sphere -200mm 52.1mm 150mm reflector rear reflector Standard plane infinity 24.2mm 50mm reflector -45° Image 15mm

[0060] In Table 1, air thickness generally refers to the distance between the center points of the optical mirrors. The center point of primary mirror 31 is the intersection of the first reflected light from the center point of front reflector 2 and primary mirror 31; the center point of secondary mirror 4 is the intersection of the second reflected light from the center point of primary mirror 31 and secondary mirror 4; and the center point of tertiary mirror 32 is the intersection of the third reflected light from the center point of secondary mirror 4 and tertiary mirror 32.

[0061] The air thickness between the center of the front reflector 2 and the center of the object space 1 is 50 mm; the air thickness between the center of the front reflector 2 and the center of the primary mirror 31 is 150 mm; the air thickness between the center of the third mirror 32 and the center of the secondary mirror 4 is 98.04 mm; the curvature radius of the spherical concave reflector is -200 mm. Figure 1 As shown in FIG, a negative curvature radius indicates that the center of the spherical concave reflector is in the opposite direction of the light propagation direction, and is used to collect the light beam. The curvature radius of the secondary mirror 4 is 100 mm.

[0062] Since the front reflector 2 and the rear reflector 5 are symmetrical about the secondary mirror 4, and the primary mirror 31 and the tertiary mirror 32 are symmetrical about the secondary mirror 4, the air thickness between the center point of the secondary mirror 4 and the center point of the tertiary mirror 32 is 98.04 mm; the air thickness between the center point of the tertiary mirror 32 and the center point of the rear reflector 5 is 150 mm, and the directions are opposite.

[0063] The radius of the front reflector 2 is 23.4 mm, and the radius of the rear reflector 5 is 24.2 mm. The outer edge of the spherical concave reflector has a radius of 52.1 mm; the outer edge of the secondary reflector 4 has a radius of 5.6 mm. The radius represents the minimum radius for zero vignetting. In actual applications, the reflector radius can be increased to account for assembly errors without obstructing the image.

[0064] The optical system of this embodiment has a numerical aperture of 0.05 and a magnification of 1. The total length of the optical system is 160 mm and the height is 170 mm. The effective imaging area is Φ30 mm. Figure 5 As shown, the time dispersion of the optical system of the present invention is 2fs.

[0065] In other embodiments, the air thickness between the center point of the front reflector 2 and the center point of the object space 1 is 50 mm, and the air thickness between the rear reflector 5 and the image space 6 is 53.717 mm. The distance between the image space 6 and the distance between the rear reflector 5 and the image space 6 is adjusted based on experimental results. When the air thickness is 53.717 mm, the image is clearest.

[0066] The Optical Transfer Function (OTF) diagram is an important tool for describing the imaging quality of an optical system. It reflects the optical system's ability to transfer signals of different spatial frequencies (such as details in an image). Figure 2 As shown, it is an OTF diagram of a low time dispersion reflective optical system of the present invention. Figure 2 Each curve represents the modulation transfer function (MTF) tested under different conditions. As the spatial frequency increases, the MTF coefficient gradually decreases, which indicates that as the image details increase, the transmission ability of the optical system decreases. Figure 2 It can be seen that the MTF is greater than 0.2 at 100lp / mm, which has a high spatial resolution.

[0067] Figure 2 Three test points are selected, namely TS0.00,0.00mm, TS 0.00,10.60mm, and TS 0.00,15.00mm, indicating that the object position is 0.00mm, 10.60mm, and 15.00mm.

[0068] like Figure 3 The following are the spot diagrams of three test points. For the first test point, the object space OBJ is 0.00, 0.00mm, and the corresponding image space IMA is 0.000, -0.010mm, indicating that the imaging position is in the negative direction of the object position and is 0.010mm away from the object.

[0069] like Figure 4 FIG. 1 shows a grid distortion diagram of a low temporal dispersion reflective optical system of the present invention. The distortion of the optical system is ≤0.08%.

[0070] The present invention also provides an ultrafast imaging streak camera, which adopts the above-mentioned low-time dispersion reflective optical system as an optical input lens.

[0071] The optical system of the present invention has small temporal dispersion, compact structure, high spatial resolution, small distortion, and wide imaging spectrum, and is suitable for picosecond wide-spectrum ultrafast imaging and sub-picosecond monochrome ultrafast imaging streak cameras.

Claims

1. A low temporal dispersion reflective optical system, characterized in that: It includes a front reflector (2), a primary mirror (31), a third mirror (32), a secondary mirror (4) and a rear reflector (5); The front reflector (2) and the rear reflector (5) are both plane reflectors, and the center points of the front reflector (2) and the rear reflector (5) are located on the same straight line, the angle between the front reflector (2) and the straight line is 45°, and the angle between the rear reflector (5) and the straight line is -45°; The front reflector (2) is used to reflect the incident light from the object side (1) to form a first reflected light; The primary mirror (31) and the third mirror (32) share a same spherical concave reflector, and the central axis of the spherical concave reflector is perpendicular to the line connecting the central points of the front reflector (2) and the rear reflector (5); The main mirror (31) is arranged on the optical path of the first reflected light and is used to reflect the first reflected light into the second reflected light; The secondary mirror (4) is a spherical convex reflecting mirror, serving as an aperture stop of the optical system; the secondary mirror (4) is coaxially arranged with the spherical concave reflecting mirror, and is used to reflect the second reflected light into the third reflected light; The three mirrors (32) are arranged on the optical path of the third reflected light and are used to reflect the third reflected light into the fourth reflected light; The rear reflector (5) is used to reflect the fourth reflected light to the image side (6).

2. The low temporal dispersion reflective optical system according to claim 1, wherein: The primary mirror (31) and the tertiary mirror (32) are rotationally symmetric about the central axis of the secondary mirror (4); The front reflector (2) and the rear reflector (5) are rotationally symmetric about the central axis of the secondary mirror (4).

3. The low temporal dispersion reflective optical system according to claim 2, wherein: The air thickness between the center point of the front reflector (2) and the center point of the object space (1) is 50 mm; The thickness of air between the center point of the front reflector (2) and the center point of the main mirror (31) is 150 mm; The thickness of air between the center point of the third mirror (32) and the center point of the secondary mirror (4) is 98.04 mm; The center point of the main mirror (31) is the intersection point of the first reflected light reflected by the center point of the front reflector (2) and the main mirror (31); The center point of the secondary mirror (4) is the intersection point of the second reflected light reflected by the center point of the primary mirror (31) and the secondary mirror (4); The center point of the three mirrors (32) is the intersection point of the third reflected light reflected by the center point of the secondary mirror (4) and the three mirrors (32).

4. The low temporal dispersion reflective optical system according to claim 3, wherein: The curvature radius of the spherical concave reflector is -200 mm; The curvature radius of the secondary mirror (4) is 100 mm.

5. The low temporal dispersion reflective optical system according to claim 4, wherein: The front reflector (2) is circular, and its radius is 23.4 mm; The radius of the circumference of the outer edge of the secondary mirror (4) is 5.6 mm; The rear reflector (5) is circular, and its radius is 24.2 mm.

6. The low temporal dispersion reflective optical system according to claim 5, wherein: The thickness of air between the center point of the front reflector (2) and the center point of the object side (1) is 50 mm; The thickness of air between the center point of the rear reflector (5) and the center point of the image side (6) is 53.717 mm.

7. A low temporal dispersion reflective optical system according to any one of claims 1 to 6, characterized in that: The front reflector (2) and the rear reflector (5) are metal film reflectors.

8. An ultrafast imaging streak camera, characterized by: A low temporal dispersion reflective optical system according to any one of claims 1 to 7 is used as an optical input lens.

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