JPH0315745A - Light waveform measuring device - Google Patents

Abstract

PURPOSE:To accurately take out the irradiation time of an optical pulse by irradiating a sample with a laser light beam whose wavelength is made shorter by a wavelength changing means, using the laser light beam as light for exciting the sample and detecting basic laser beam transmitted through the wavelength changing means. CONSTITUTION:A semiconductor laser 1 is excited by a current pulse from a pulse power source 2, whose rise is quick, and outputs the optical pulse 9 whose duration is short. The pulse 9 is made incident on the wavelength changing means 10, which outputs the 2nd higher harmonic 12 of the laser light beam having the half wavelength of the pulse 9. The sample 3 is placed in the output direction of the higher harmonic 12 and emits fluorescence by receiving the higher harmonic 12 from the means 10. By irradiating the sample 3 with the laser beam whose wavelength is made shorter by the means 10 and using the laser beam as the light for exciting the sample, the sample 3 is irradiated with the laser beam whose wavelength is short in a state where the small-sized laser 1 is taken as a light source.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical waveform measuring device that measures the optical waveform of light to be measured emitted from a sample by irradiating the sample with a laser beam.

[Conventional technology]

As an example of an optical waveform measuring device that measures the optical waveform of the light to be measured emitted from the sample by irradiating the sample with a laser beam, for example,
Devices that can measure fluorescence lifetime using time-correlated single photon counting are known.

This time-correlated single photon counting method will be briefly explained.

The sample is irradiated with a light pulse of sufficiently short duration, the photons of fluorescence emitted from the sample are detected by this irradiation, and the time from irradiation of the light pulse to the detection of the photons of fluorescence is measured. . In addition, for one light pulse irradiation, at most 1
It is adjusted to such an extent that only 1 photon can be detected. and,
By repeating this time measurement many times (approximately 1 million times to obtain highly accurate results) and expressing the obtained data in a histogram, the fluorescence lifetime characteristics (light waveform) of the sample can be obtained. .

Optical waveform measuring devices, including fluorescent lifetime measuring devices for obtaining such fluorescent lifetime characteristics, are equipped with light sources and photodetectors necessary to measure optical waveforms such as fluorescent lifetime characteristics.

Incidentally, flash lamps, gas lasers, and the like have traditionally been used as light sources for these optical waveform measuring devices, but recently semiconductor lasers, which are small and easy to use, have gradually come to be used.

[Problem to be solved by the invention]

However, the wavelength of semiconductor lasers currently in practical use is 600 nm or more, and if you want to irradiate a sample with a light pulse with a wavelength shorter than this, you can use a gas laser, etc., which also requires large-scale equipment. I was using it. For this reason, when trying to irradiate a sample with a short wavelength light pulse, there was a problem in that the size of the apparatus became large.

[Means to solve the problem]

In order to solve the above problems, the optical waveform measurement device of the present invention uses a semiconductor laser as an optical pulse light source, and is equipped with a wavelength conversion means that shortens the wavelength of the laser light output from the semiconductor laser and irradiates the sample with the laser light. There is. Furthermore, in the optical waveform measurement device of the present invention, in order to prevent the intensity of the irradiated light onto the sample from becoming too weak, the fundamental laser light that passes through the wavelength conversion means without being wavelength converted is detected. It includes a first photodetector and a measuring means for measuring the optical waveform of the light to be measured emitted from the sample based on the output of the first photodetector.

[Effect]

With this configuration, the sample is irradiated with light emitted from the semiconductor laser and shortened in wavelength by the wavelength conversion means. The light to be measured is emitted from the sample by the irradiation of the short wavelength light, and the waveform of the light is measured by the measuring means. On the other hand, the fundamental laser beam that has passed through the wavelength conversion means is output at the same timing as the shortened wavelength light, and is detected by the first photodetector. Therefore, by measuring the optical waveform based on the detection output of the first photodetector, it becomes possible to accurately measure the optical waveform.

〔Example〕

FIG. 1 is a block diagram showing one embodiment of the present invention.

A semiconductor laser (laser diode) 1 is connected to a pulse power source 2
It is excited by a current pulse with a fast rise, and outputs a sufficiently short optical pulse (pulsed laser beam) 9 having a duration of ins or less. In this embodiment, the light pulse 9 output from the semiconductor laser 1 is a red laser beam with a wavelength of 820 nm, and is incident on the wavelength conversion means 10.

The wavelength conversion means 10 is made of an optical crystal material (for example, lithium niobate [LiNbO3]) having a nonlinear optical effect, and converts a laser beam having a wavelength of one-half of the incident laser beam 9, that is, a blue laser beam having a wavelength of 410 nm. Outputs 2nd harmonic 12. A sample 3 is placed in the output direction of the second harmonic 12, and the sample 3 receives the second harmonic 12 from the wavelength conversion means 10 and emits fluorescence.

In this way, by irradiating the sample 3 with the laser light whose wavelength has been shortened by the wavelength conversion means 10 and using it as sample excitation light, it is possible to use the small and easy-to-use semiconductor laser 1 as the light source. It is now possible to irradiate the sample 3 with laser light of a short wavelength, which was previously not possible with a semiconductor laser.

By the way, in order to perform the time-correlated single photon counting method,
It is necessary to accurately detect the time from irradiating the sample with a light pulse to detecting a photon of fluorescence, and for this purpose it is necessary to obtain a measurement start signal, which is the reference for starting time measurement, every time a light pulse is irradiated. be.

In order to obtain this measurement start signal, conventionally, the light pulse irradiated onto the sample 3 is split using a semi-transparent mirror, the split light is detected by a photodetector, etc., and this detection output is used as the measurement start signal. there was. The purpose of using a translucent mirror that requires an optical setup is that if the electric pulse that drives the optical pulse light source is used directly as the measurement start signal,
This is because the time between the actual irradiation time of the light pulse and the measurement start signal cannot be kept constant due to drift due to temperature changes in the pulsed light source section.

However, the light intensity of the second harmonic 12 output from the wavelength converting means 10 is 1 to 2% of the light intensity of the laser beam 9 incident on the wavelength converting means 10, and is quite weak. Therefore, as mentioned above, when trying to obtain a measurement start signal by branching the second harmonic 12, which is a light pulse irradiated onto the sample 3, using a semi-transparent mirror, etc., the intensity of the irradiation light on the sample 3 and the measurement start signal are The intensity of the branched light becomes extremely weak.

Therefore, in the present invention, we focus on the fact that the fundamental wave 11 transmitted through the wavelength conversion means 10 and outputted has the same timing as the second harmonic 12 and has a strong light intensity, and utilizes this fundamental wave 11. The measurement start signal is obtained. That is, in the direction in which the fundamental wave l1 of the wavelength conversion means 10 is output, a first photodetector 4 made of, for example, a photodiode is provided, and its detection output is used as a measurement start signal as a time voltage. Converter (time-to-aIIpl
itudeconverter; TAC)
It is input to the start terminal of 5.

On the other hand, the second harmonic 12 radiated from the wavelength conversion means 10
is irradiated onto the sample 3, one photon of fluorescence is emitted from the sample 3.
3 is output. The second photodetector 6 detects photons 1 of this fluorescence.
3, and is composed of, for example, a photomultiplier tube. The detection output of this photodetector 6 is input to the stop terminal of the TAC 5. Here, conditions are set such that one photon 13 is detected only after the sample 3 is irradiated with several tens of light pulses.

The TAC 5 is a device that outputs a voltage pulse having a height proportional to the time difference between the signal input to the start terminal and the signal input to the stop terminal. Therefore, the output actually has a height corresponding to the time from the light pulse irradiation of the semiconductor laser 1 to the fluorescence photon emission of the sample 3, although there is a delay corresponding to the propagation time of the laser light and the detection output. It becomes a voltage pulse. As mentioned above, since the conditions are such that one photon l3 is detected for every tens of irradiations, the voltage pulse is output from the TAC 5 at the measurement start signal of several tens of times. This happens only once in all the times I entered it.

The output terminal of TAC5 is connected to a pulse height analyzer (pulseheig).
ht anallzer; P H A ) 7 input terminal. The PHA 7 is a device that digitizes and stores the height of input voltage pulses and counts the number of pulses according to the height of the pulse, and together with the TAC 5 constitutes a fluorescence life characteristic calculation means 8.

Figure 2 shows how many voltage pulses are applied to PHA7 from TAC5.
This figure shows an example of the counting results of the PHA 7 when given to . In this figure, the vertical axis indicates the probability that a photon 13 will be detected at that time, and its value is proportional to the fluorescence intensity at that time. Therefore, this diagram directly represents the temporal change in fluorescence intensity, that is, the fluorescence lifetime characteristic. in fact,
Light pulses are irradiated one million to tens of millions of times, and measurements are continued until approximately one million photons are detected, and the fluorescence lifetime characteristics are calculated based on the measurement results.

FIG. 3 is a block diagram of an embodiment of the present invention different from the embodiment described above. Note that the same parts as in the embodiment described above are given the same reference numerals, and the explanation thereof will be omitted.

In this embodiment, a streak camera 5o is used instead of the TAC 5, PHA 7, and photodetector 6. The structure and operation of this streak camera will be briefly explained with reference to FIG. As shown in Figure 4,
The streak camera 50 is a camera 5 that captures a streak image obtained by the streak tube 52 and the streak tube.
It is composed of 3. Measured light 51 emitted from the sample and measured by the streak camera reaches the photocathode 55 of the streak tube 52 through an input optical system such as a slit (not shown) and a lens (not shown). The light is converted into electrons at a photocathode 55, and the converted electrons are accelerated by an accelerating electrode 56 and passed through a deflection plate 57 to a micro channel plate.
plate ; M C P ) 5 8. When the electrons pass between the deflection plates 57, the electrons pass between the deflection plates 57.
7 is swept by a sweep voltage applied between the MC
Reach P58. The electrons that have reached the MCP 58 are multiplied here and cause the fluorescent light 60 to emit light, forming a streak image. This streak image can be captured by a camera 53 placed behind the fluorescent surface 60. Incidentally, the timing at which the sweep voltage is applied to the deflection plates 57 needs to match the timing at which electrons pass between the deflection plates 57. For this reason, the detection output of the first photodetector 4 is input to the streak camera 50 as a trigger signal for starting the sweep operation, and in response to this input, the sweep voltage generator 6
2 generates a sweep voltage and applies it to the deflection plate 57.

Then, the second harmonic 12 is transmitted from the wavelength conversion means 10 to the sample 3.
When the sample 3 is irradiated with the measured light 51, the sample 3 emits the measured light 51. This measured light 51 enters the streak camera 50,
The streak camera 50 measures a temporal change in the light intensity (light waveform) of the light to be measured 51 emitted from the sample 3 as a streak image.

This measurement is repeated, and the obtained streak images are integrated by an image processing device (not shown), etc., and a streak image with a good signal-to-noise ratio (S/N ratio), that is, an optical waveform of the light to be measured, is It is now possible to obtain

Note that the streak camera 50 shown in FIGS. 3 and 4
Instead, a sampling type optical waveform observation means can also be used.

An example of the structure and operation of this sampling type optical waveform observation means will be briefly explained with reference to FIG. The sampling type optical waveform observation means shown in FIG. 5 mainly includes a sampling type streak tube 65 and an information processing system that processes information regarding the optical waveform of the measured light obtained by extracting a part of the measured light 51 using the sampling type streak tube 65. 66. The light to be measured 51 emitted from the sample and observed by the sampling type optical waveform observation means is focused by the lens 67 onto the photocathode 68 of the sampling type streak tube 65 . This incident light is converted into electrons according to the light intensity on the charging surface 68, and the converted electrons are accelerated by the accelerating electrode 70, pass between the deflection plates 71, and pass through the slit plate 7.
2.

When the electrons pass between the deflection plates 71, the electrons pass between the deflection plates 71
It is swept by the sweep voltage applied between them and reaches the slit plate 72. Since the slit plate 72 has minute slits perpendicular to the sweep direction, only a part of the electrons that have reached the slit plate 72 pass through this slit.
It reaches the fluorescent surface 73 behind it. The fluorescent surface 73 emits light by collision with electrons. This emission intensity is the photomultiplier tube 7
5, amplified by amplifier 76, and output as an electrical signal. In this way, the light to be measured 5
The signal obtained by sampling the light intensity of 1 is stored in the information processing section 66.

Such a sampling operation is repeated by sequentially shifting the sweep timing slightly with respect to the incident timing of the light to be measured, so that the optical waveform as shown in Fig. 6 can be obtained from the information obtained by 1q. It has become.

Note that the detection output of the first photodetector 4 is input to the sampling streak tube 65, and the application of the sweep voltage to the deflection plate 71 is based on the sampling of the detection output of the first photodetector 4. The timing is sequentially shifted from the time when the data is input to the mold streak tube 65.

〔Effect of the invention〕

As explained above, according to the optical waveform measuring device of the present invention, a laser beam whose wavelength has been shortened by the wavelength conversion means is irradiated onto a sample to be used as sample excitation light, and at the same time, the laser beam is transmitted through the wavelength conversion means. Since the fundamental wave laser beam is detected and the optical waveform is measured based on this detection output, the irradiation time of the optical pulse can be accurately determined without reducing the intensity of the laser beam irradiated onto the sample from the wavelength conversion means. can be taken out.

1... Semiconductor laser, 2... Pulse power supply, 3...
sample, 4... first photodetector, 5... time voltage converter (TAC), 6... second photodetector, 7... pulse height analyzer (PHA), 8...・Method for calculating fluorescence life characteristics;
10... Wavelength conversion means, 50... Streak camera, 65... Sampling type streak tube.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a graph showing calculation results of PHA7, and FIG. 3 is an embodiment of the present invention, which is different from the embodiment shown in FIG. Block diagrams of different embodiments, FIG. 4 is a structural diagram of a streak camera, FIG. 5 is a structural diagram of a sampling type optical waveform observation means, and FIG. 6 is a diagram of an optical waveform obtained using the sampling type optical waveform observation means. This is the graph shown.

Claims (1)

[Claims] 1. An optical waveform measuring device that measures light to be measured emitted from the sample by irradiating the sample with laser light, the device comprising: a semiconductor laser;
A wavelength conversion means for shortening the wavelength of the laser light from the semiconductor laser and irradiating it onto the sample; and a first wavelength conversion means for detecting the laser light having the fundamental wavelength of the semiconductor laser that passes through the wavelength conversion means.
a photodetector, and the output of the first photodetector is input,
An optical waveform measuring device comprising: a measuring means for measuring the optical waveform of the light to be measured based on this output. 2. The optical waveform measuring device according to claim 1, wherein the measuring means is a streak camera that performs a sweeping operation based on the output of the first photodetector. 3. The optical waveform measuring device according to claim 1, wherein the measuring means is a sampling type optical waveform observing means that operates based on the output of the first photodetector. 4. The measuring means includes a second photodetector that detects photons of constant light from the sample, and a time period from the output of the first photodetector to the output of the second photodetector. Claim 1, further comprising: means for measuring a plurality of times and calculating a light waveform from a sample by a time-correlated single photon counting method.
The optical waveform measuring device described.