JPS5845524A - Method and device for time-resolved spectroscopy by single photon counting method - Google Patents

Abstract

PURPOSE:To improve time resolving power to the order of picoseconds or nanoseconds by forming the image of the secondary light from a sample cell to a slender region in parallel with the long axis direction of the photoelectric cathode surface of a side on type electron multiplier. CONSTITUTION:The secondary photons released from an energized sample are made incident to a side on type photoelectron multiplier 10 through a lens 9 in such a way that the slit image thereof is formed in the optimum position on a photoelectric cathode surface in parallel with the long axis direction thereof. The anodic current pulses obtained from the multiplier 10 start a time difference-to-crest converter 18. On the other hand, the pulse signal of reference light detected with a photoelectric detecting element 14 stops the converter 18, whereby the output corresponding to the time difference between the reference light and the secondary light is obtained. The secondary light is made incident from the sample cell to the multiplier 10 without decrease in the quantity of said light, whereby jitters are decreased considerably and high time resolving power is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a time-resolved spectroscopy method and apparatus using a time-correlated single photon counting method, and particularly to improvements for obtaining time resolution in the picosecond to nanosecond range.

Time-resolved spectrometers include phase method, streak camera method,
Optical shutter methods, optical gating methods, and time-correlated single photon counting methods are commonly used. Among these methods, the phase method has a short measurement time and high accuracy, but the
The III-determination of the complicated relaxation process of secondary light has the drawback of insufficient time resolution, making it difficult to analyze. In addition, the streak camera method, optical shutter method, and optical gate method all have a time resolution of picoseconds or more, but they generally have low sensitivity and a poor signal-to-noise ratio, making it difficult to understand the complex light emission process of the sample. Difficult to handle. On the other hand, the time-correlated single photon counting method is characterized by extremely high sensitivity, and because it has a wide and wide range between time and count values, it is suitable for systems with weak luminescence or multi-component luminescence processes. Therefore, its application is extremely wide-ranging.

However, in the time-resolved spectroscopy systems based on the time-correlated single photon counting method that have been put into practical use to date, the time resolution is only on the order of nanoseconds or sub-nanoseconds, and as a result, the measurement targets are limited, making them difficult to measure. 90 In general, a time-resolved spectrometer using the time-correlated single photon counting method consists of a pulsed light source, a sample cell, a ninth detection means for obtaining a reference signal, and a light pulse from the light source that is divided between the sample cell and the detection means. A splitter for dispersing the secondary light from the sample cell, a spectroscopic means for dispersing the secondary light from the sample cell, a photomultiplier tube for detecting the secondary light tubes for counting, a discriminator for discriminating the wave height of the output of the photomultiplier tube, and a discriminator. It is equipped with a time difference measuring device that measures the time difference between the output and the reference signal. Since a pulsed light source has a finite pulse width and the response speed of the photomultiplier tube and electric circuit is also finite, it is difficult to calculate the true relaxation curve of the secondary light emitted from the sample excited by the light pulse of the light source. In order to obtain this, it is necessary to deconvolve the transition curve obtained by measurement with the response function of the device itself. However, in this case, fluctuations in the emission time width, emission intensity, and pulse shape of the pulsed light source, jitter of the photomultiplier tube, jitter and drift of the electric circuit, etc., cause the width and time fluctuation of the so-called device-specific response function. When the deconvolution is enlarged, the deconvolution becomes difficult), and the time-resolved stacking becomes worse.

In recent years, the application of laser stems as light sources for this type of spectroscopic system has progressed, and in order to easily obtain stable and narrow optical pulses from CW mode-locked lasers, 1K] and Mara electronic circuits have been developed. As stable IF and IC devices are now available, photomultiplier tube jitter is the biggest factor in the time-resolved resolution [K] of spectroscopic systems.

In general, in photomultiplier tubes, the transit time of electrons is controlled by the established processes involved in photoelectron and secondary electron emission, but also depends on the photon impact position and photon energy; This rounding may be considered to be the cause of jitter in the transmission time of
) type photomultiplier tube was used, but heads type photomultiplier tubes were expensive, large and difficult to handle, and the jitter was minimal and stopped at 250 picoseconds.The purpose of this invention is , a time-resolved spectroscopy method using a single photon counting method that uses an inexpensive and compact side-on photomultiplier to further reduce jitter and thereby improve the time resolution to the picosecond or nanosecond order. There are plans to provide the equipment.

That is, in the time-resolved spectroscopy method using the single-photon counting method of the present invention, a side-on type photomultiplier tube is used as a photomultiplier tube for photoelectron counting, and the secondary light from the sample cell is converted into a side-on type photomultiplier tube. An image is formed on a narrow region parallel to the long axis direction of the photocathode surface of the multiplier tube, and the voltage applied between the photocathode and the first dynode of the id-on photomultiplier tube is set to a high voltage of 300 V or more. In addition, in the time-resolved spectrometer of the present invention used for such a spectroscopic method, the side-on type photomultiplier tube and a narrow width parallel to the long axis direction of the photocathode surface of the photomultiplier tube are provided. It is equipped with an optical system consisting of a lens or a mirror that images the secondary light onto a region.

According to this invention, a time-resolved spectroscopy system using single-photon counting method that can handle up to the picosecond region will be realized, and therefore it will be possible to precisely measure the relaxation process that is faster than conventional methods. It also facilitates temporal separation of scattering and fluorescence, which greatly contributes to precision measurements not only in physical and chemical fields but also in various fields such as medicine and biology. The details are as follows.

FIG. 1 is a block diagram showing the system configuration of a time-resolved spectrometer according to an embodiment of the present invention, in which (1) shows the pulsed light [
, (2) hub beam splitter, (3) lens, (4
) is a mirror, (5) is a sample cell, (6) is a lens, (7
) is the aperture, (8) is a spectroscopic means such as a monochromator or filter, (9) is a slit imaging lens, and the ring is a side-on photomultiplier tube, CLI
(2) is a high-voltage power source for the photomultiplier tube, and a pulse height discriminator that compares and discriminates the wave height of the anode current pulse output from the photomultiplier tube with a predetermined reference value; (2) is a lens, - is a photoelectric detection element such as a photodiode, - is an amplifier, 輔 is a pulse height discriminator similar to the above, @ line delay circuit,
■ is a time-difference wave height converter, (to) is a multi-channel wave height analyzer, beam splitter (2) and a $300 lens (3).
], through the sample cell (5) and spectrometer & (8) to the pulse height discriminator @ constitutes the first channel system (starting channel), and from the lens to the photoelectric detection element and the delay circuit (2 ) to the pulse height discriminator @ constitutes the second channel system (stop channel), and the time difference pulse height converter and multichannel pulse height analyzer (2) constitute the signal processing section. A data processing device including a recording device or a display device (not shown) is connected to the analyzer and analyzer (b). The pulsed light source (1) preferably generates stable light pulses with a narrow emission time width. It is preferable to use a light source that can select an arbitrary wavelength if possible. Generally, a discharge gap flashier lamp has been used as a pulsed light source in this type of spectroscopic system, but in this invention, the Noculus width can be narrowed, the pulse shape is stable, and the beam can be In view of the unexamined decomposition characteristics in the picosecond to nanosecond region, such as excellent monochromaticity and directionality, it is particularly desirable to use a CW mode-locked laser as a pulsed light source. It is preferable to use a mode-locked gas laser or a CW mode-locked dye laser as a wavelength variable pulsed light source. Figure 2 shows a 1kc cell suitable for use as a pulsed light source (1).
This is a block diagram showing an example of a w-mode-locked laser system, which includes a single-wavelength pulsed light source (1a) consisting of an ion laser for CW mode-locking, and a CW mode-locked laser system using the same laser.
9I variable wavelength pulsed light from %-dosynchronized dye laser
(1b), either of the light sources can be selectively used depending on the requirements, such as an OCW mode-locked or ion laser pulsed light source (1a), a CW argon ion laser ( 101) output mirror (10!S
) so that the resonator length is approximately 18Qa*.
A CW laser beam with a wavelength of 9 to 514.5 from the peak of the entire argon laser line is obtained, and by placing a crystal oscillator in this resonator, the CW laser beam is converted into a pulsed beam of a desired frequency. A part of this pulsed light beam is outputted as a beam (119), and a part of this pulsed light beam is sent to a beam splitter (104) and a baller (119).
4) to a photoelectric detector (115), and the output current of the detector (115) causes the laser power source (116
) to stabilize the laser output and pulse width. The acousto-optic modulator (102) is made by cutting both sides of a hexahedron made of quartz glass at the Brewster angle, and depositing 262 LlNbO5 crystals on one side of the gold coating.
It is installed as a vibrator with a thickness of μm, and depending on its temperature, it is possible to select a resonance frequency of about 150 and every 20 around a center frequency of 40.
In FIG. 2, reference numeral (118) is a temperature regulator for this temperature control.

A CW mode-locked dye laser pulse light source (1b) sends the pulsed light beam (119) to a beam splitter (1
05) and rhodamine 6 formed in a resonator of the same length as the resonator of the CW argon ion laser (101) by guiding with balers (106), (107), and (108).
synchronously exciting a dye jet stream (110) such as G;
For example, 5 wavelengths are selected using a refracted filter (112).
It is designed to obtain pulsed light (120) with a desired wavelength of 40 to 640 nm. Note that (116) is an output mirror, and (109) (111) is a mirror that forms a resonator together with the output mirror (113).

By the way, according to the above example, the average output of the 514.5 mm wavelength of the CW mode-locked or ion laser pulsed light source (1 m) is 100 mW, the pulse width is about 200 picoseconds, and the average output is 9 CW.
The output pulse width of the mode-locked dye laser pulse light source (1b) is approximately 10 picoseconds.

Of course, it should be noted that in addition to the above example as the light source (υ), another gas laser or dye laser may be used, or the wavelength of the excitation light may be selected by using a double wave or double wave. The O sample cell (5) may be one for ordinary Raman scattering or fluorescence measurement, but the O spectroscopy means (8), which is particularly preferably used in microcells and flow cells, is, for example, a spectroscopic monochromatic cell. It is a monochromator (monochromator), and can be replaced with a filter.Also, a PIN photodiode is optimal for the photoelectric detection element.
The delay circuit aη, the time-difference pulse height converter (2), the multichannel pulse height analyzer (4), etc. can be selected from those used in ordinary radiation detection devices, and can be easily integrated into ICs. As the pulse height discriminator, a type that detects the peak position of the input is particularly preferable.

It is preferable to use the photomultiplier tube Q (of the lFi nide size type) by cooling it to below -20° C. with a cooler 4 from the viewpoint of reducing darkness and noise.

FIG. 93 schematically shows the arrangement of the side-on photomultiplier tube αq and the slit imaging lens (9) in relation to the exit slit (2) of the spectroscopic means (8). Since the ion type photomultiplier tube has a more complex structure than the ion type photomultiplier tube, it has the disadvantage that the travel time of electrons will vary greatly if the incident light is applied to the entire surface of the ion beam. . Regarding the relationship between the peak point position and pulse width of the incident light pulse with respect to the positions in the long axis direction and the short axis direction of the photocathode surface, the relative peak point position is 10 at any point in the long axis direction. It was confirmed that the pulse width was constant within picoseconds, but it changed sharply in the short axis direction, and that the pulse width was constant at any position on either the long or short axis, except at both end positions in the short axis direction. Therefore, in the present invention, a lens (9) or a concave mirror is placed after the exit slit (2) of the middle spectroscopic stage (8).
A narrow slit 1i is imaged at an optimal position near the center of the photocathode surface in parallel to the long axis direction of the photocathode 1i, thereby preventing the secondary light from the sample cell from decreasing in light intensity. The photomultiplier tube (7) is made to enter the side-on type photomultiplier tube (7), and the jitter, which was conventionally 1 nanosecond, is significantly reduced and high time resolution is obtained. Since it is smaller than the head type, the transit time of the electrons can be shortened by increasing the applied voltage, and the fluctuation in timing with respect to the rise 9 of the incident optical pulse is reduced to a total applied voltage of 1000 V. In this invention, the photoelectric aS and l! By applying a voltage of 300 V or more, preferably 400 V or more, to the first dynode and applying a voltage that is normally used in subsequent stages, it is possible to connect the photocathode surface and the first dynode without damaging the photomultiplier tube. This shortens the electron transit time between dynodes and extremely minimizes the difference in electron transit time depending on the wavelength of incident light.

The voltage applied to each dynode of such a photomultiplier tube can be set as desired by adjusting the total applied voltage and leader resistance value using a high voltage source (11).

In the time-resolved spectrometer according to the present invention having the above configuration, a light pulse from the light source (1) is first split into excitation light for the first channel system and reference light for the WJ2 channel by the beam splitter (2). The excitation light irradiates and excites the sample (5), and the reference light is detected by a photoelectric detection element to provide a time reference for time difference measurement. Excited sample (5)
The secondary light emitted from the spectrometer (8) is separated by the spectrometer (8), and the secondary light is output from the output slit (2) of the spectrometer (8) until the slit image is located at the optimum position on the photocathode surface. The light is incident on the side-on photomultiplier tube through the entire lens (9) so as to form an image parallel to the axial direction. Spectroscopic means (
The aperture (7) on the incident side of 8) is used to weaken the secondary light so that the number of photons of the secondary light detected by the photomultiplier tube is one or less per one pulse of excitation light. used. The anode current pulse obtained from the photomultiplier tube is waveform-shaped by erasing the dark current pulse at the head of the pulse height discriminator. After that, the time-difference pulse height converter is activated, while the above-mentioned photoelectric detection element is The reference light pulse signal detected by the pulse height discriminator and the delay circuit stops the time difference pulse height converter, thereby converting the voltage output corresponding to the time difference between the reference light and the secondary light. This voltage output taken from low 0 is analyzed by a multi-channel pulse height analyzer (2) for every n photon detected by a side-on photomultiplier, resulting in a time-resolved signal representing the photon emission frequency versus the time difference. A profile is obtained by a recording device or a display device (not shown). This profile indicates the relationship between the time after the excitation pulse light is irradiated onto the sample and the intensity of the 92-order light emitted during that time. Figure 1114 shows, as an example, the obtained scattered light intensity (dashed line) and fluorescent light intensity (
The time-resolved profile of the intensity for the O scattered light shown by the time-resolved profile of the sample cell (solid line)
) was obtained by placing a known scatterer such as ground glass in place of the sample and matching the spectral wavelength of the spectroscopic means (8) with the wavelength of the excitation light. This corresponds to an equipment function determined by the time width and intensity fluctuations of the photomultiplier tube, jitter of the photomultiplier tube, etc. The true time-resolved profile of fluorescence intensity relaxation is obtained by deconvoluting the actually measured time-resolved profile of the fluorescence intensity with the time-resolved profile of the scattered light intensity, that is, the instrument function. It would be better to process the output using a microcomputer.

As described above, according to the present invention, whereas conventional head-on type photomultiplier tubes, which were expensive and difficult to handle due to their large size, were used, this is an inexpensive and small side-on type photomultiplier tube. Not only can it be replaced with a tube, but it can also obtain high temporal resolution, and time-resolved profiles can be reproduced within a range of 10 picoseconds, precise deconvolution is possible, and time correlation Time-resolved spectroscopy using the single-photon counting method can now provide more accurate and reliable time-resolved profiles, making it widely applicable to measurements of Raman scattering spectra and fluorescence intensity relaxation.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a system configuration according to an embodiment of the present invention, FIG. 2 is a block diagram showing an example of the system configuration of the light source, and FIG. 3 is a side-on photomultiplier tube and its incident light. A perspective view schematically showing the situation with the slit imaging means, and Figures 1 to 4 are diagrams showing an example of the obtained time-resolved profile. (1): Pulse light source, (2): Beam splitter, (
5): sample cell, (7) near aperture, (8): spectroscopic means, (9) Nislit imaging lens, (Q: side-on photomultiplier tube, α1: high voltage source, μs = pulse height discriminator , -Two photoelectric detection elements, @: Wave height discriminator % @: Delay circuit,
-: Time difference pulse height converter, (2): Multichannel pulse height analyzer, (2): Exit slit, - Two photocathodes, @) Nisrit Wei. Agent Patent Attorney Tadashi Sato Year 1□1 Figure 2 0 b de 0 Figure 4-4-? J-nel wo-1

Claims (1)

[Scope of Claims] (1) A side-on photomultiplier is used as a photomultiplier for photoelectron counting, and secondary light from the sample cell is transferred to the photocathode surface of the side-on photomultiplier. A time-resolved spectroscopy method using a single photon counting method, which is characterized by focusing on a narrow region parallel to the long axis direction. (2) A side-son type photomultiplier tube is used as a photomultiplier tube for photoelectron counting, and the charging cathode of the photomultiplier tube and the first
The applied voltage between the dynode and the dynode t-! 100V or more,
Time-resolved spectroscopy using a single photon counting method, characterized in that secondary light from a sample cell is imaged onto a narrow region parallel to the long axis direction of the photocathode surface of the side-effect photomultiplier tube. Method. (3) Consisting of a pulsed light source, a 111 channel system, a @2 channel system, and a signal processing section, and the first channel system includes a sample cell that is excited by a light pulse from the light source, and a sample cell that is excited by a light pulse from the light source. The wL2 channel system includes a spectroscopy means for dispersing n secondary light emitted from the cell, and a photomultiplier tube that is heated by a high-voltage power source and detects the dissected secondary light for counting. includes a detection means for obtaining a reference signal from a light pulse from the light source, and is based on a single photon counting method that discriminates the pulse height of the photoelectron signal from the photomultiplier tube and measures the time difference with the reference signal in the signal processing section. In the time-resolved spectroscopy device, a side-on type photomultiplier tube is provided as the photomultiplier tube, and secondary light from the spectroscopic means is provided in a narrow region parallel to the long axis direction of the photocathode surface of the photomultiplier tube. A time-resolved spectroscopy device characterized by being equipped with an optical system that forms an image of light (4) The charged cathode of the side-son photomultiplier tube and @1
The applied voltage between the dynode and the high voltage power supply is J)
Time-resolved spectroscopy device according to claim 8, item 3, characterized in that the voltage is 300 V or more.The time-resolved spectrometer according to claim 3, which uses a cw laser synchronized laser as a pulsed light source. Time-resolved spectrometer. (6) The optical system includes an exit slit of the spectroscopic means,
4. The time-resolved spectroscopy apparatus according to claim 3, further comprising a lens that causes an image of the exit slit to be focused on the photocathode surface as the narrow region.