A new chopper blade for distinguishing positive and negative signals

Abstract

The present invention discloses a new type of chopper blade for distinguishing positive and negative signals, which has the following characteristics: a disc-shaped body; a central circular hole, located at the center of the disc-shaped body, for installing the shaft of the disc-shaped body; a fixing part, including three small holes evenly distributed around the central circular hole, through which screws pass to fix the disc-shaped body on the base of the chopper. Among them, the disc-shaped body is designed with fan-shaped hollows and rectangular hollows, the number of fan-shaped hollows is multiple, all located outside the fixing part and evenly arranged along the circumferential direction, the number of rectangular hollows is plural, all located in the outermost layer of the disc-shaped body and evenly arranged along the circumferential direction, and the fan-shaped and rectangular hollows are used for the base of the chopper to detect the rotation speed of the disc-shaped body and perform negative feedback regulation, so as to stabilize the rotation speed of the disc-shaped body at the set frequency.

Description

Technical Field

[0001] The invention relates to the field of laser measurement, and in particular to a novel chopper blade for distinguishing positive and negative signals. Background Art

[0002] Studying and measuring the dynamic process of internal carriers of a sample when it is excited is the main method to study ultrafast charge transfer in materials. Currently, the main research technology is based on time-resolved pump-probe technology based on ultrafast lasers.

[0003] Figure 1 Schematic diagram of the time-resolved pump-probe system.

[0004] like Figure 1 As shown in the figure, one of the two ultrashort pulse lasers has a higher energy (generally higher than the optical band gap of the material), which is used as pump light (Pump), changing the properties of the material and causing the particles to transition from the ground state to an unstable high-energy state. The other delayed pulse light (Probe) with weaker energy is used as probe light to illuminate the area of ​​the sample that has just been excited. By adjusting the position of the reflector on the electric translation stage to change the optical path difference between the two beams of light reaching the sample, the time delay between the probe light and the pump light can be changed accordingly. Since the excited sample is in a non-equilibrium state, the transmitted light or reflected light signal after passing through the sample will change in the process of returning to the ground state equilibrium state. Therefore, using optical signal detectors, such as spectrometers and CCDs, optical signals at different delay times can be recorded to infer transient information of physical or chemical changes in the substance.

[0005] Figure 2 Schematic diagram of the pump-probe system.

[0006] As shown in Figure 2, a femtosecond laser with a central wavelength of 800 nm, a pulse width of 100 fs, and a repetition frequency of 1000 Hz emits fundamental frequency pulse light, which is divided into two beams of pump light and detection light by a beam splitter (BS) with a splitting ratio of 1:3.

[0007] When the pump light passes through the electric translation stage, the time delay line is adjusted to achieve the delay between the pump light and the detection light. According to the needs of the actual sample during the experiment, the nonlinear frequency doubling crystal (BBO) is inserted or removed in the pump light path to switch the pump light between the two wavelengths of 400nm and 800nm. Then the chopper is used to modulate it to achieve the alternation of pump light and no pump light, and after being properly attenuated by the attenuator, it is focused on the sample surface to achieve the excitation of the sample.

[0008] The probe light passes through the lens and is focused on a sapphire crystal (Sapphire Plate), thereby generating a wide-spectrum supercontinuum white light with a wavelength range of 500nm to 1000nm. The generated white light is focused on the sample, and the probe light and the pump light are overlapped in time and space on the sample surface. Finally, the probe light that passes through the sample carries the state information of the particles after being excited. The spectrometer separates the components according to different wavelengths, and then detects them with the spectral CCD, so as to record and analyze the time evolution process of the sample recovering from the excited state to the ground state after the pump light.

[0009] The key component of the pump-probe system is the optical chopper. The fundamental frequency of the femtosecond pulse laser has a high repetition frequency (1KHz). Relative to the particle evolution process in the sample at the picosecond and nanosecond time scales, the pump-probe experiment is actually a set of high-frequency repetitive experiments. When Chopper modulation is not used, the pump light and the probe light have the same frequency, and a single event starts when a pump pulse reaches the sample and ends when the next pump pulse reaches the sample, with a period of 1ms.

[0010] Figure 3 Schematic diagram of the timing of pump light and probe light pulses.

[0011] like Figure 3 As shown, the horizontal axis T is the absolute time when the pulse reaches the sample.

[0012] According to the principle of transient absorption spectroscopy, it is necessary to detect the detection signal T corresponding to the presence and absence of pump light. pump on , T pump off Therefore, a Chopper is needed to realize the switching of pump light, i.e. modulation. The laboratory originally used the MC 2000 Optical Chopper from Thorlabs.

[0013] Figure 4 Schematic diagram of Thorlabs' MC 2000 Optical Chopper.

[0014] like Figure 4 As shown in the figure, it uses a phase-locked loop (PLL) speed controller to accurately control the chopping speed and ensure that the phase is consistent with the reference signal. The chopper allows external reference signal input and has a phase adjustment function, which is of great help in using the output signal of the laser amplifier stage as the chopping reference signal to achieve synchronous pulse modulation and always maintain phase stability during system construction.

[0015] After receiving the 1KHz electrical signal from the femtosecond laser, Chopper uses this signal as a reference, operates at 500Hz, and modulates the pump light to 500Hz.

[0016] Figure 5 This is a schematic diagram of the chopper's operating timing.

[0017] like Figure 5 As shown, from top to bottom is the signal timing of the detection light, laser electrical signal, optical chopper and pump light.

[0018] Chopper modulates the pump light to 500Hz and hits the sample, and then the detector irradiates the sample, carrying the state information of the particles inside the sample after being excited and received by the spectrometer and CCD. When there is pump light, the transmitted light (T pumped ) and the detected transmitted light (T unpumped ) will be arranged alternately, and the difference between the two is the relative change of the transmitted light intensity

[0019]

[0020] This is the detected signal.

[0021] However, although the signal received by the CCD is known to be the intensity information of a column of alternately arranged detection transmission light, when using Thorlabs' Chopper, it is impossible to know whether the starting point of the data is the detection light intensity with or without pump light. Therefore, the calculated difference can only get the correct absolute value, but the positive and negative of the signal cannot be determined. Therefore, a method or device that can obtain the positive and negative values ​​of the detection signal without changing the measurement principle and system is urgently needed. Summary of the invention

[0022] The present invention is made to solve the above-mentioned problem, and its purpose is to provide a new chopper blade for distinguishing positive and negative signals.

[0023] The present invention provides a new type of chopper blade for distinguishing positive and negative signals, which is used in a pump detection system and installed on a chopper for judging the positive and negative of a spectral signal. The blade has the following characteristics: a disc-shaped body; a central circular hole located at the center of the disc-shaped body for installing the axis of the disc-shaped body; a fixing portion including three small holes evenly distributed around the central circular hole, through which screws are passed to fix the disc-shaped body on the base of the chopper. The disc-shaped body is designed with fan-shaped hollows and rectangular hollows, the number of fan-shaped hollows is multiple, all located outside the fixing portion and evenly arranged along the circumferential direction, the number of rectangular hollows is plural, all located on the outermost layer of the disc-shaped body and evenly arranged along the circumferential direction, and the fan-shaped and rectangular hollows are used for the base of the chopper to detect the rotation speed of the disc-shaped body and perform negative feedback regulation to stabilize the rotation speed of the disc-shaped body at a set frequency.

[0024] The novel chopper blade for distinguishing positive and negative signals provided by the present invention may also have the following feature: wherein the diameter of the disc-shaped main body is 100 to 104 mm.

[0025] The novel chopper blade for distinguishing positive and negative signals provided by the present invention may also have the following feature: wherein the diameter of the central circular hole is 5 to 7 mm.

[0026] The novel chopper blade for distinguishing positive and negative signals provided by the present invention may also have the following characteristics: the area ratio of the hollowing out of the fan-shaped shape to the non-hollowing out of the fan-shaped shape is 1:2, and the number of hollowing out of the fan-shaped shape is 10 to 16.

[0027] The new chopper blade for distinguishing positive and negative signals provided by the present invention may also have the following characteristics: wherein the rectangular hollowing out and the rectangular non-hollowing out divide the outer circumference of the circular sheet-shaped body into equal parts, the area ratio of the rectangular hollowing out and the rectangular non-hollowing out is 1:1, and the number of the rectangular hollowing out is 10 to 16.

[0028] The novel chopper blade for distinguishing positive and negative signals provided by the present invention may also have the following characteristics: wherein, every three adjacent fan-shaped hollows correspond to four adjacent rectangular-shaped hollows, and the fan-shaped hollows aligned with the rectangular-shaped hollows and the fan-shaped hollows aligned with the middle parts of the two rectangular-shaped hollows are alternately arranged adjacent to each other.

[0029] The novel chopper blade for distinguishing positive and negative signals provided by the present invention may also have the following features: wherein the disc-shaped main body is made of an aluminum plate, and the surface is oxidized black to achieve the purpose of shielding the laser.

[0030] Functions and Effects of the Invention

[0031] According to the new chopper blade for distinguishing positive and negative signals involved in the present invention, it includes: a disc-shaped body; a central circular hole, located at the center of the disc-shaped body, for installing the shaft of the disc-shaped body; a fixing part, including three small holes evenly distributed around the central circular hole, and screws pass through the small holes to fix the disc-shaped body on the base of the chopper. Among them, the disc-shaped body is designed with fan-shaped hollows and rectangular hollows, the number of fan-shaped hollows is multiple, all located outside the fixing part and evenly arranged along the circumferential direction, the number of rectangular hollows is plural, all located in the outermost layer of the disc-shaped body and evenly arranged along the circumferential direction, and the fan-shaped and rectangular hollows are used for the base of the chopper to detect the rotation speed of the disc-shaped body and perform negative feedback regulation to stabilize the rotation speed of the disc-shaped body at the set frequency.

[0032] In addition, since the original chopper blade modulates the 1KHz pump light to 500Hz, the sample signal detected by the probe light is excited (T pumped ) and unexcited (T unpumped ) are arranged alternately. After analysis, the spectral signal of the sample can be obtained, but it is impossible to know which group of data is the excited or unexcited signal, resulting in the inability to determine whether the signal is positive or negative.

[0033] Therefore, the new chopper blade for distinguishing positive and negative signals of the present invention modulates the 1KHz pump light in another way, so that the sample signal carried by the detection light becomes a single excited (T pumped ) and the second unexcited (T unpumped )’s signal is arranged periodically, so that the positive and negative of the sample’s spectral signal can be analyzed and the correct transient absorption spectrum can be obtained, solving the problem that the original chopper could not solve. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of a time-resolved pump-probe system in the prior art;

[0035] Figure 2 It is a schematic diagram of a pump-probe system in the prior art;

[0036] Figure 3 It is a time schematic diagram of pump light and probe light pulses in the prior art;

[0037] Figure 4 is a schematic diagram of the MC 2000 optical chopper of Thorlabs in the prior art;

[0038] Figure 5 It is a schematic diagram of the working timing of the chopper in the prior art;

[0039] Figure 6 is a schematic diagram of a novel chopper blade for distinguishing positive and negative signals in an embodiment of the present invention;

[0040] Figure 7 is a schematic diagram of a signal arrangement method after using a new blade in an embodiment of the present invention;

[0041] Figure 8 is a transient absorption spectrum of PBDB-T in an embodiment of the present invention (single-point measurement method);

[0042] Fig. 9 (a), (b) and (c) are respectively three signal arrangement diagrams of the transient absorption spectrum of the sample in the embodiment of the present invention;

[0043] Fig.10 are three curves measured by PTY6 in the 720-1000 nm band in the embodiments of the present invention; and

[0044] Fig.11 It is a curve diagram obtained by performing cross-correlation operation on three curves in pairs in the embodiment of the present invention. DETAILED DESCRIPTION

[0045] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the following embodiments are combined with the accompanying drawings to specifically explain the new chopper blade for distinguishing positive and negative signals of the present invention.

[0046] This embodiment provides a new chopper blade for distinguishing positive and negative signals. It is used in a pump-detection system, and can be used in conjunction with an electric translation stage and a spectral CCD to obtain a transient absorption signal of a sample at a continuous wavelength.

[0047] Figure 6 Schematic diagram of a novel chopper blade for distinguishing positive and negative signals in this embodiment.

[0048] like Figure 6 As shown, the novel chopper blade 100 for distinguishing positive and negative signals in this embodiment includes a disc-shaped body 10 , a central circular hole 20 , a fixing portion 30 , a fan-shaped hollow 40 , and a rectangular hollow 50 .

[0049] The diameter of the disc-shaped main body 10 is 102 mm, and the material is an aluminum plate, and the surface is oxidized black to achieve the purpose of shielding the laser.

[0050] The central circular hole 20 is located at the center of the disc-shaped body 10 and is used to install the shaft of the disc-shaped body 10. The diameter of the central circular hole 20 is 6 mm.

[0051] The fixing portion 30 includes three small holes evenly distributed around the central circular hole, and screws pass through the small holes to fix the disc-shaped body 10 on the base of the chopper.

[0052] The disc-shaped main body 10 is designed with a sector-shaped hollow 40 and a rectangular-shaped hollow 50 .

[0053] There are ten sector-shaped hollows 40, all of which are located outside the fixing portion 30 and are evenly arranged along the circumferential direction. The area ratio of the sector-shaped hollows 40 to the sector-shaped non-hollows is 1:2.

[0054] There are 15 rectangular hollows 50 and 15 rectangular non-hollows arranged alternately. They are all located on the outermost layer of the disc-shaped body 10 and are evenly arranged along the circumferential direction. The area ratio of the rectangular hollows 50 to the rectangular non-hollows is 1:1.

[0055] Every three adjacent fan-shaped hollows 40 correspond to four adjacent rectangular hollows 50, and the fan-shaped hollows 40 aligned with the rectangular hollows 50 and the fan-shaped hollows 40 aligned with the middle parts of two rectangular hollows 50 are alternately arranged adjacent to each other.

[0056] The sector-shaped hollow 40 and the rectangular hollow 50 are used for the base of the chopper to detect the rotation speed of the disc-shaped body 10 and perform negative feedback regulation to stabilize the rotation speed of the disc-shaped body 10 at a set frequency.

[0057] In this embodiment, a chopper using a new chopper blade 100 for distinguishing positive and negative signals is installed in the system, and the signal received by the spectrometer and CCD will no longer be T pumped and T unpumped Alternately arranged, but with T pumped , T unpumped , T unpumped The arrangement is repeated for one cycle. There is a difference between the detection transmission light when the sample is excited and when it is not excited. By analyzing this difference, the arrangement of the signal can be known. In fact, there are three signal arrangement methods according to the different starting points of the signal. If On represents the detection transmission light when excited and Off represents the detection transmission light when not excited, then the signal arrangement method depends on whether the detection transmission light at the starting point corresponds to the excitement.

[0058] Figure 7 It is a schematic diagram of the signal arrangement after using the new blade in this embodiment.

[0059] like Figure 7 As shown, the signal arrangement method includes three situations shown in the figure, which are arranged alternately.

[0060] Taking a known sample PBDB-T as an example, a Chopper equipped with a new blade is used to access the system for detection. After obtaining the data, a point is randomly selected as the starting point. Assume that the light intensity signal at the starting point is T pumped , followed by two consecutive T unpumped , which can divide the data into three groups. Use the formula for the one-two, one-three, and two-three groups:

[0061]

[0062] The relative change in the intensity of the transmitted light can be calculated, and by plotting the relative change versus wavelength, three curves that may be the transient absorption spectra of the sample can be obtained.

[0063] Figure 8 It is the transient absorption spectrum of PBDB-T in this embodiment (single-point measurement method).

[0064] like Figure 8 As shown, the three curves are drawn in the same figure. After a simple analysis, the correct signal can be obtained.

[0065] Fig. 9 (a), (b) and (c) are respectively diagrams of three signal arrangement situations of the transient absorption spectrum of the sample in this embodiment.

[0066] like Fig. 9 As shown, there may be three situations for the three curves in one figure, and only the part with a wavelength of 550-720nm is shown in the figure.

[0067] In the first case, the first and second curves are the same, and the third curve has no signal, so the first and second curves both represent the correct signal; in the second case, the first and third curves are opposite signals, and the second curve has no signal, so the third curve represents the correct signal; in the third case, the second and third curves are the same, and the first curve has no signal, so the second and third curves are opposite to the correct signal. If the experimental data is obtained through correct experimental operation, then there are only these three cases.

[0068] If we perform one-dimensional cross-correlation operations on the three curves, we have:

[0069]

[0070] Then when the two curves are similar, there will be a very high correlation peak; if the two curves have opposite signals, there will be a negative correlation peak; if one of the curves has no signal, the cross-correlation result will be a curve that fluctuates around zero. In this way, the similarity relationship between the three curves can be quickly determined, and then the correct signal can be determined.

[0071] Fig.10These are three curves measured by PTY6 in the 720-1000nm band in this embodiment.

[0072] like Fig.10 As shown, taking the 720-1000nm band of sample PTY6 as an example, in this embodiment, the 800nm ​​part has a very poor signal due to the influence of pump light scattering, so it is shielded in advance.

[0073] Perform cross-correlation operation on the three measured curves.

[0074] Fig.11 This is a curve diagram obtained by performing cross-correlation calculation on three curves in this embodiment.

[0075] like Fig.11 As shown in the figure, the first three figures are no correlation peak, negative correlation peak and positive correlation peak respectively. After judging the positive and negative relationship of the three curves, it can be obtained that the correct transient absorption spectrum signal of PTY6 in the 720-1000nm band should be Fig.11 The fourth picture in.

[0076] Functions and Effects of the Embodiments

[0077] According to the new chopper blade for distinguishing positive and negative signals involved in this embodiment, it includes: a disc-shaped body; a central circular hole, located at the center of the disc-shaped body, for installing the shaft of the disc-shaped body; a fixing part, including three small holes evenly distributed around the central circular hole, and screws pass through the small holes to fix the disc-shaped body on the base of the chopper. Among them, the disc-shaped body is designed with fan-shaped hollows and rectangular hollows, the number of fan-shaped hollows is multiple, all located outside the fixing part and evenly arranged along the circumferential direction, the number of rectangular hollows is plural, all located in the outermost layer of the disc-shaped body and evenly arranged along the circumferential direction, and the fan-shaped and rectangular hollows are used for the base of the chopper to detect the rotation speed of the disc-shaped body and perform negative feedback regulation to stabilize the rotation speed of the disc-shaped body at the set frequency.

[0078] In addition, since the original chopper blade modulates the 1KHz pump light to 500Hz, the sample signal detected by the probe light is excited (T pumped ) and unexcited (T unpumped ) are arranged alternately. After analysis, the spectral signal of the sample can be obtained, but it is impossible to know which group of data is the excited or unexcited signal, resulting in the inability to determine whether the signal is positive or negative.

[0079] Therefore, the new chopper blade for distinguishing positive and negative signals in this embodiment modulates the 1KHz pump light in another way, so that the sample signal carried by the detection light becomes a single excited (T pumped ) and the second unexcited (T unpumped)’s signal is arranged periodically, so that the positive and negative of the sample’s spectral signal can be analyzed and the correct transient absorption spectrum can be obtained, solving the problem that the original chopper could not solve.

[0080] The above-mentioned embodiments are preferred examples of the present invention and are not intended to limit the protection scope of the present invention.

Claims

1. A chopper blade for distinguishing positive and negative signals, used in a pump detection system and installed on a chopper for judging the positive and negative of a spectral signal, characterized in that: include: A disc-shaped body, the disc-shaped body is made of an aluminum plate, and the surface is oxidized black to achieve the purpose of shielding the laser; A central circular hole, located at the center of the disc-shaped body, for mounting the shaft of the disc-shaped body; The fixing part includes three small holes evenly distributed around the central circular hole, and screws pass through the small holes to fix the disc-shaped body on the base of the chopper. The disc-shaped body is designed with fan-shaped hollows and rectangular hollows. The number of the fan-shaped hollows is multiple, all located outside the fixing portion and evenly arranged along the circumferential direction, the area ratio of the fan-shaped hollows to the fan-shaped non-hollows is 1:2, and the number of the fan-shaped hollows is 10 to 16, The number of the rectangular hollows is plural, all of which are located on the outermost layer of the disc-shaped body and are evenly arranged along the circumferential direction. The rectangular hollows and the rectangular non-hollows divide the outer circumference of the disc-shaped body into equal parts. The area ratio of the rectangular hollows and the rectangular non-hollows is 1:

1. The number of the rectangular hollows is 10 to 16. The hollowing out of the fan-shaped and rectangular shapes is used for the base of the chopper to detect the rotation speed of the disc-shaped body and perform negative feedback regulation to stabilize the rotation speed of the disc-shaped body at a set frequency. The method for the chopper blade to distinguish positive and negative signals is as follows: The signal received by the spectrometer and CCD is T pumped , T unpumped , T unpumped Repeat the arrangement for a cycle.

2. The chopper blade for distinguishing positive and negative signals according to claim 1, characterized in that: in, The diameter of the disc-shaped main body is 100-104 mm.

3. The chopper blade for distinguishing positive and negative signals according to claim 1, characterized in that: in, The diameter of the central circular hole is 5-7 mm.

4. The chopper blade for distinguishing positive and negative signals according to claim 1, characterized in that: in, Every three adjacent hollowings in the fan-shaped shape correspond to four adjacent hollowings in the rectangular shape, The fan-shaped hollows located at positions aligned with the rectangular hollows and the fan-shaped hollows located at positions aligned with middle portions of the two rectangular hollows are alternately arranged adjacent to each other.

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