JP2656106B2 - Optical waveform measurement device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to an optical waveform measuring device, and is used, for example, for measuring the lifetime of fluorescent light generated when a measurement object is irradiated with laser light.

[Conventional technology]

As a conventional optical waveform measuring device having a high time resolution, for example, the following is known. The first is a time-correlation single-photon counting method, which irradiates an object to be measured with a light pulse having a sufficiently short duration, detects fluorescent photons emitted from the object by this irradiation, and generates an optical signal. The time from irradiating the pulse to detecting a fluorescent photon is measured.

The second one uses a streak camera device, and measures the waveform of light from the object to be measured by a streak camera tube that performs a sweep operation of an electron beam in synchronization with irradiation of a light pulse. According to this, the light waveform can be measured even in the first case by repeating the light pulse irradiation and the sweep operation many times. Further, even when a large number of photons are generated from the measured object by one pulse light irradiation, the optical waveform can be measured.

As the optical waveform measuring device, in addition to the above cases, a sampling optical waveform measuring device using a sampling streak tube, a device using a pin photodiode, an avalanche photodiode as a photodetector, and the like are known. .

For such a measurement, a signal serving as a reference for starting the measurement must be given. For example, in the time-correlation single-photon counting method, measurement cannot be performed unless a start signal (start signal) for time measurement is given, and in the case of using a streak camera, measurement is not possible without a start signal (trigger signal) for sweeping. It is. Therefore, the signal which is a reference for starting the measurement is obtained by the conventional device as follows. First
In this technique, a pulse light from a laser light source is branched by a half mirror or the like, one of the excitation light is irradiated to a sample, and the other is guided to a photodetector to obtain a measurement start signal. The second is to take out the signal itself given to the drive circuit of the semiconductor laser constituting the laser light source and use it as a measurement start signal.

[Problems to be solved by the invention]

However, according to the first method, an optical system for splitting an optical pulse is required, and the configuration is complicated.
In addition, since the pulse light is split, the effective use of the light amount is not sufficient. According to the second method, drift and jitter occur between the electric signal and the output of the pulse light in the drive circuit of the pulse light source, and the temporal relationship between the measurement start signal and the timing of the pulse light can be kept constant. Disappears. For this reason, especially when performing a plurality of counts, it is difficult to improve the time resolution because the timing is shifted for each count. In addition, since a detection circuit and the like are provided, the circuit configuration becomes complicated.

Therefore, an object of the present invention is to provide an optical waveform measuring apparatus which has a simple configuration, can effectively use the amount of pulsed light from a light source, and can increase the time resolution.

[Means for solving the problem]

An optical waveform measurement device according to the present invention is an optical waveform measurement device that measures an optical waveform of light to be measured generated when a sample is irradiated with pulsed light, and a light emitting element such as a semiconductor laser that emits pulsed light, An electric signal source that outputs an electric drive signal for driving the semiconductor light emitting element; and a branching unit that branches the electric drive signal between the electric signal source and the semiconductor light emitting element as a step voltage, a pulse voltage, a sine wave voltage, or the like. And measuring means for measuring the optical waveform of the light to be measured by sweeping the photoelectrons obtained by detecting the light to be measured based on the electric drive signal branched by the branching means.

[Action]

According to the present invention, the signal for sweeping the photoelectrons generated by the incidence of the light to be measured is obtained by branching from the electric drive signal itself for driving the semiconductor light emitting element (laser) as the pulse light source, so that the drive circuit The timing of the sweep operation of the pulsed light and the photoelectron does not shift due to drift or jitter of the pulse.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a configuration diagram of an optical waveform measuring device according to a first embodiment of the present invention. In FIG. 1, a voltage generator 1 outputs an electric drive signal such as a pulse voltage, a step voltage or a sine wave voltage of a predetermined frequency. The electric drive signal from the voltage generator 1 100Psec
Is changed to a short-pulse current (electric pulse signal) having a fast rise time and supplied to the semiconductor laser LD. As a result, the semiconductor laser LD emits ultrashort pulses of several tens of Psec in accordance with the known current-light output (IL) characteristics. Semiconductor laser LD
Irradiates the measurement object (sample 3) via an optical lens system (not shown), whereby fluorescent light PL is generated from the sample 3. The fluorescent light PL is received by the streak camera device 7 described later in detail, and photoelectrons are generated.

On the other hand, a part of the electric drive signal from the voltage generator 1 is branched by the branch unit 2 including a coil, a resistor, and the like, and provided to the streak camera device 7 via the delay line 5 and the filter 6. Here, the delay line 5 functions as a trigger delay for adjusting the timing between the fluorescent light PL and the sweep operation of the streak camera device 7, and the filter 6 functions as the voltage generator 1
This serves as a means for adjusting the rise time of the electric drive signal from the camera, thereby making the time range of the streak camera device 7 variable. Data relating to the streak camera image obtained by the streak camera device 7 is read into the reading device 8 and subjected to predetermined analysis processing.

As described above, since the semiconductor laser LD and the streak camera device 7 are driven by the same signal (electric drive signal) from the voltage generator 1, there is a difference between the generation timing of the fluorescent light PL and the sweep timing of the streak camera device 7. Does not occur. Therefore, there is an effect that the time resolution is not deteriorated even when the streak image is settled for a long time.

FIG. 2 is a detailed configuration diagram of the optical waveform measuring device shown in FIG. 1, and FIG. 3 is a signal waveform diagram of each part thereof.

As shown in FIG. 2, a capacitor C having a small capacity is provided between the branching device 2 and the semiconductor laser LD, and a pulse-like electric drive signal from the voltage generator 1 (V ₁ shown in FIG. 3A).
As a result, an extremely short pulse voltage (V ₂ shown in FIG. 3 (b)) having a very fast rise can be obtained. Therefore, several tens of Psec as shown in FIG.
An ultrashort pulse light LB having a short pulse width is output. Here, the output voltage from the voltage generator 1 is several hundred [V], but the voltage for driving the semiconductor laser LD may be several [V].
The value of the capacitor C may be small. Accordingly, only the electrical drive signal from the voltage generator 1 (falling portion of the V ₁₎ higher component frequency component of (pulse voltage V ₁₎ is applied to the semiconductor laser LD as V _2. That is, since the impedance Z of the capacitor C is Z = 2π · fc, the higher the frequency component, the lower the impedance.

The filter 6 shown in FIG. 2 includes a passive element 61 including a resistor, a capacitor, an inductor, and the like, and the sweep speed of the streak camera device 7 can be selected by switching the passive element 61 with a switch. The streak camera device 7 includes a streak tube 71, a lens 72 on the light input side, and a lens 73 on the streak image output side. The streak tube 71 has a photocathode 74 for emitting photoelectrons in response to the fluorescent light PL, an accelerating electrode 75 for accelerating electrons from the photocathode 74, and a focusing electrode for forming an electron beam emitted from the photocathode 74 on the MCP. (Not shown),
It has a deflecting electrode 76 for deflecting the accelerated electrons EB, a microchannel plate (MCP) 77 for multiplying the electrons EB, and a fluorescent screen 78 for emitting fluorescence by irradiation of electrons.
Then, the streak image formed on the fluorescent screen 78 is picked up by the reading device 8 having, for example, a CCD, taken in as data, and subjected to processing such as integration and analysis.

The optical waveform measuring device shown in FIG. 2 operates as follows.

First, when the short pulse current V ₂ generated by the capacitor C is sent to the semiconductor laser LD via the voltage generator 1 and the branching device 2, the fluorescent light PL is generated from the sample 3, and the fluorescent light PL is generated by the streak camera device 7. Swept as photoelectrons. here,
To the deflection electrode 76 of the streak camera device 7, an electric drive signal (pulse voltage) branched by the branch unit 2 and subjected to delay or the like is sent as a streak sweep voltage. That is, since the sweep voltage is generated based on the electric drive signal itself output from the voltage generator 1, even if the voltage generator 1 or the like has drift or jitter, the laser LD of the present invention is used.
The relationship between the light emission timing and the streak sweep timing is kept constant. Therefore, the sample 3
In synchronization with the irradiation of the ultrashort pulse light LB, the sweep of the streak camera device 7 is started.

In that embodiment, one ultrashort pulse LB on sample 3
When many photons are emitted as fluorescent PL by irradiation of
It is also possible to observe the optical waveform by one sweep. That is, since the streak tube 71 is used, a plurality of photons may be generated for one irradiation of the ultrashort pulse light LB. However, when a large number of photons are not emitted at once, the light emission of the semiconductor laser LD and the sweeping of the streak camera device 7 may be repeated a plurality of times, and the data of the streak images obtained thereby may be accumulated and integrated.

FIG. 4 is a configuration diagram of an optical waveform measuring device according to a second embodiment. In this embodiment, a voltage generator 1 having a sine-wave oscillator 11 and an amplifier 12 is used. This sine-wave voltage is split by a splitter 2 and one is sent to a comb generator 22 and the other is a resonance circuit 65. Sent to The comb generator 22 is composed of, for example, a step coverage diode and forms a waveform shaping means. The comb generator 22 inputs a sine wave like a waveform A shown in FIG. 4 and outputs a pulse wave like a waveform C shown in FIG. The pulse waveform C is a short pulse of about 100 Psec and has the same repetition as the frequency of the input sine wave A. The pulse waveform C from such a comb generator 22
Is input to the semiconductor laser LD, the semiconductor laser LD outputs an ultrashort pulse light LB having a pulse width of several tens of Psec.

The resonance circuit 65 selects a resonance frequency for the frequency of the input sine wave A, and is resonated between the deflection electrode 76 and a capacitor. As a result, a high-voltage sine wave is applied to the deflection electrode 76, and a high-speed scan called a synchro scan is performed. Also in the second embodiment, the sample 3
Since the timing of the ultrashort pulse light LB irradiated on the streak camera and the timing of the sweep in the streak camera device 7 are completely synchronized, the time resolution can be significantly improved.

Note that, instead of the streak camera device 7 shown in the first and second embodiments, a sampling type optical waveform observation unit can be used.

An example of the structure of the sampling type optical waveform observation means and its operation will be briefly described with reference to FIG. Fifth
The sampling type optical waveform observing means shown in the figure is mainly composed of a sampling type streak tube 91 and an information processing unit 100 for processing information relating to the optical waveform of the measured light obtained by extracting a part of the measured light PL. It is composed of The measured light PL radiated from the sample 3 and observed by the sampling optical waveform observation means is focused on the photoelectric surface 93 of the sampling streak tube 91 by the lens 92. This incident light is converted by the photocathode 93 into electrons corresponding to the light intensity, and the converted electrons are accelerated by the accelerating electrode 94, pass between the deflecting plates 95, and are guided to the slit plate 96.
When passing between the electron deflecting plates 95, the slit plate 96 is swept by the sweep voltage applied between the deflecting plates 95,
To reach.

Here, the sweep voltage is obtained by delaying the step voltage or the like from the voltage generator 1 by a predetermined delay or the like. A semiconductor laser for irradiating the sample 3 with a signal obtained by branching the step voltage by the branch unit 2 is used. The LD is emitting light. Therefore, the timing of incidence of the ultrashort pulse light LB on the sample 3 and the timing of streak sweeping by the sampling streak tube are completely synchronized.

Since a small slit perpendicular to the sweep direction is formed in the slit plate 96, only a part of the electrons that have reached the slit plate 96 pass through this slit and reach the fluorescent surface 97 behind the slit. The fluorescent screen 97 emits light due to the collision of electrons, and a streak image is formed. This emission intensity is based on a photomultiplier tube (PMT) 9
It is caught by 8, amplified by the amplifier 99, and output as an electric signal. The signal obtained by sampling the light intensity of the measured light PL in this manner is output to the information processing unit.
It is stored in 100.

Such a sampling operation is repeated with the timing of sweeping slightly shifted sequentially with respect to the incident timing of the light to be measured from the sample 3, and an optical waveform is obtained from the obtained information as shown in FIG. You can do it.

Note that a wavelength conversion element may be provided on the emission surface side of the semiconductor laser, or a spectroscope may be provided between the sample and the measuring means.

[Effects of the Invention] As described above in detail, according to the present invention, a signal for sweeping photoelectrons by light to be measured is obtained from an electric signal itself for driving a semiconductor light emitting element (laser) as a pulse light source. Therefore, the timing of pulse light and streak sweeping does not shift due to drift or jitter of the driving circuit or the like. Further, it is not necessary to provide a special detection circuit. Therefore, the optical waveform observation device of the present invention has a simple configuration, can effectively use the amount of pulsed light from the light source, and can increase the time resolution.

[Brief description of the drawings]

FIG. 1 is a block diagram of an optical waveform measuring device according to a first embodiment of the present invention, FIG. 2 is a diagram showing a detailed configuration of the device of the first embodiment, and FIG. 3 is a signal of each part in FIG. Waveform diagrams, FIG. 4 is a configuration diagram of an optical waveform measurement device according to a second embodiment, and FIGS. 5 and 6 are explanatory diagrams of a configuration and operation of an optical waveform measurement device according to another embodiment. DESCRIPTION OF SYMBOLS 1 ... Voltage generator, 2 ... Divider, 22 ... Com generator, 3 ... Sample, 5 ... Delay line, 6 ... Filter, 7
…… Streak camera device, 71 …… Streak tube, 91…
… Sampling streak tube, LD …… semiconductor laser,
LB: Ultra short pulse light, PL: Fluorescence.

Claims (4)

(57) [Claims] 1. An optical waveform measuring apparatus for measuring an optical waveform of light to be measured generated when a sample is irradiated with pulsed light, wherein the semiconductor light emitting element irradiates the pulsed light and the semiconductor light emitting element is driven. An electric signal source that outputs an electric drive signal for, and a branching unit that branches the electric drive signal between the electric signal source and the semiconductor light emitting element, and a photoelectron obtained by detecting the light to be measured, An optical waveform measuring apparatus, comprising: a measuring unit configured to measure an optical waveform of the measured light by performing a sweep based on the electric drive signal branched by the branching unit. 2. An optical waveform measuring apparatus according to claim 1, wherein said measuring means comprises a streak camera device for performing a sweeping operation based on said branched electric drive signal. 3. An optical waveform measuring apparatus according to claim 1, wherein a waveform shaping means having a step recovery diode is interposed between said branching means and said semiconductor light emitting device. 4. An optical waveform measuring apparatus according to claim 1, wherein said measuring means comprises a sampling type optical waveform observing apparatus which performs a sweeping operation based on the branched electric drive signal.