JPH0422811A - Light/heat displacement microscope - Google Patents

Abstract

PURPOSE:To obtain a microscope hard to receive the influence of a noise and vibration from the outside by forming a focal point on a sample by modulating the output light of a semiconductor laser, and detecting reflected light with a displacement detecting optical system. CONSTITUTION:The output of an oscillator 3 is formed in a rectangular wave with constant frequency, and the output of the semiconductor laser 1 is modulated at a driving circuit 2. The output light of the laser 1 transmits a beam splitter 4, and forms the focal point on the sample 6 with an objective lens 5. The reflected light from the sample 6 passes the lens 5, and is reflected on the beam splitter 4, and is made incident on the columnar lens 71 of the displacement detecting optical system 7, and a circular image is formed on a quadripartite photodiode 72. The circular image is changed to an image of vertically elongated ellipse or that of laterally elongated ellipse from the circular image corresponding to the displacement of the sample 6 arranged at the focusing position of the lens 5. Such image is detected by each element comprising the quadripartite photodiode 72, respectively, and is converted to an electrical signal. A signal in accordance with the displacement of the sample 6 can be obtained by taking the difference of the diagonal sum of the electrical signal.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a signal detection method of a photothermal displacement microscope and to improvement of device performance.

<Prior art> Generally, when an object is irradiated with intermittent light, the object repeatedly expands and contracts, causing pressure fluctuations in the object and its surroundings (photoacoustic effect).The photoacoustic signal generated by this photoacoustic effect is used to An image of the sample can be obtained by scanning the sample surface with intermittent light focused by an optical microscope.

FIG. 4 is a block diagram showing a conventional example of a photothermal displacement microscope that utilizes such a photoacoustic effect, and has a configuration in which a microphone is used for signal detection.

In FIG. 4, a sample 22 placed in a sealed cell 21 is irradiated with intermittent light focused by an objective lens 23. Part of this light is reflected by the surface, and the rest is reflected by the sample 22.
absorbed into. The absorbed light energy turns into heat,
diffuses into the sample 22.

A part of the diffused heat is transmitted to the gas near the surface of the sample 22, and the gas expands and contracts. Therefore, the pressure inside the cell 21 increases and acoustic waves are generated. This is detected by the microphone 24, and the signal from the microphone 24 is synchronously amplified by the lock-in amplifier 25 and recorded. In order to obtain a two-dimensional image of the sample 22, the cell 21 is moved to an X-Y moving table 26.
All you have to do is fix it on the top and scan it.

<Problems to be Solved by the Invention> However, in the photothermal displacement device shown in the above-mentioned prior art, the sound pressure of the acoustic wave generated by the photoacoustic effect is 10'
Since it is very small, about Pa, and close to the detection limit of the microphone 24, the measurement results in a poor S/N ratio. Also, since the microphone 24 is easily affected by external noise and vibration, a lock-in amplifier 25 is used for signal amplification.
are using. However, since it is necessary to narrow the bandwidth, the time constant is increased, which increases the measurement time.

Furthermore, since the sealed cell 21 is required, the structure is complicated, and there are problems such as the size of the sample 22 that can be measured is diluted.

The present invention has been made based on the problems of the prior art described above, and aims to provide a photothermal displacement reference WL mirror that has a good S/N ratio and is less susceptible to external noise and vibration. There is nothing.

Means for Solving the Problems> The configuration of the present invention for solving the above problems includes a semiconductor laser, a drive circuit for modulating the output light of the semiconductor laser, and a drive circuit for modulating the output light of the semiconductor laser onto a sample. an objective lens to narrow down the light, a beam splitter to guide the reflected light from the sample to the displacement detection optical system (described later), a displacement detection optical system to detect minute displacements of the sample, and a The present invention is characterized in that it is provided with a displacement signal processing circuit that converts the output of the displacement signal into a displacement signal.

Effect> According to the present invention, the displacement of the sample surface by modulated light is detected, and a sample cell is not required, making the device simpler and less susceptible to external noise and vibration. can.

<Example> Hereinafter, the present invention will be explained based on the drawings.

FIG. 1 is a configuration diagram showing an embodiment of a photothermal displacement microscope according to the present invention. In FIG. 1, 1 is a semiconductor laser, 2 is a drive circuit for the semiconductor laser 1, 3 is an oscillator, 4 is a beam splitter, and 5 is an objective lens incorporating a linear actuator. can. Reference numeral 6 indicates a measurement sample, and 7 indicates a displacement detection optical system for detecting minute displacements of the sample 6. For example, as shown in FIG. shall be. 8 is a displacement signal processing circuit with an automatic gain control function, which calculates a displacement signal from the output signal of the displacement detection optical system 7. A lock-in amplifier 9 amplifies the output of the displacement signal processing circuit 8 in synchronization with the output of the oscillator 3. 10 is a control circuit for the linear actuator of the objective lens 5, and 11 is a sample hold circuit.

The operation of such a configuration will be explained using the operation waveform diagrams shown in FIGS. 1, 2, and 3. Figure 3 (
As shown in FIG. 3B, the output of the oscillator 3 is converted into a rectangular wave of a certain constant frequency, and the output of the oscillator 1 is modulated between Pl and 22 by the drive circuit 2 (FIG. 3B). The output light of the semiconductor laser 1 passes through the beam sublime 4,
The reflected light from the sample 6, which is focused on the sample 6 by the objective lens 5, passes through the objective lens 5 and passes through the beam splitter 4.
, and enters the cylindrical lens 71 of the displacement detection optical system 7 . The incident light forms a circular image on a four-segment photodiode 72 installed at the focal position of the cylindrical lens 71 in the χ and V directions. This circular image changes from a circle to an image of a vertically long ellipse or a horizontally long ellipse in response to the displacement of the sample 6 placed at the focal point position of the objective lens 5 (Fig. 2).
Each element constituting the divided photodiode 72 detects the light and converts it into an electrical signal. By calculating the difference between the diagonal sums of these electrical signals, a signal corresponding to the displacement of the sample 6 can be obtained. Note that the amount of reflected light changes depending on the modulated light power of the semiconductor laser 1 and the reflectance of the sample. By dividing the difference signal of the diagonal sums of each element of the four-divided photodiode 72 by the sum signal of the diagonal sums in the displacement signal processing circuit 8,
A displacement output (FIG. 3 (c)) synchronized with the modulation signal is obtained. This displacement output is input to the lock-in amplifier 9, where it is amplified in synchronization with the output of the oscillator 3, and an output corresponding to the amount of displacement (FIG. 3 (d)) is obtained. Further, the displacement output of the displacement signal processing circuit 8 is inputted to the control circuit 810, and the displacement output of the displacement signal processing circuit 8 is inputted to the control circuit 810, and
Focus position control is performed. During measurement, the sample hold circuit 11 holds the control signal from the control circuit 10 to hold the objective lens 5 at a constant position.

In the above embodiment, the configuration of the displacement detection optical system 7 is not limited to the astigmatism method using the cylindrical lens 71 and the 4-part photodiode 72, but can also be used for focal position error detection such as the Knifezi method or the critical angle method. You may also use the law.

<Effects of the Invention> As described above in detail with the embodiments, according to the present invention, (1) The displacement detection optical system 7 can be designed as desired, and can detect a displacement of 10n1 or less. It is possible to detect. Since this is sufficiently small compared to the displacement due to thermal expansion, measurement with a good S/N ratio is possible.

(2) Since the lock-in amplifier 9 may have a wide bandwidth, the time constant can be made small and the measurement time can be shortened.

(3) Since the displacement of the sample surface due to modulated light is detected, a sample cell is not required, sideways are easier, and restrictions on sample size are reduced. Moreover, it is not affected by external noise.

(4) Since the semiconductor laser 1, objective lens 5, and displacement detection optical system 7 can be integrated, the sameness can be increased and the influence of external vibrations can be reduced.

(5) Since the focus point can be controlled using the displacement signal, the structure is simple and there is no need to adjust the focus position every time the sample moves, so the waiting time during measurement is shortened and measurement can be performed quickly.

It is possible to realize a photothermal displacement mirror W1 having the following effects.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the photothermal displacement microscope of the present invention, FIG. 2 is a block diagram showing a specific example of the displacement detection optical system used in the device shown in FIG. 1, and FIG. FIG. 4 is an operation waveform diagram for explaining the operation of the apparatus, and FIG. 4 is a conventional example. DESCRIPTION OF SYMBOLS 1... Semiconductor laser, 2... Drive circuit, 3... Oscillator, 4... Beam splitter, 5... Objective lens, 6... Measurement sample, 7... Displacement detection optical system 58・・・
・Displacement signal processing circuit, 9...Lock-in amplifier, 10
...Control circuit, 11...Sample hold circuit, 7
1... Cylindrical lens, 72... 4-segment photodiode.

Claims (1)

[Claims] A semiconductor laser, a drive circuit for modulating the output light of the semiconductor laser, an objective lens for focusing the output light of the semiconductor laser onto the sample, and guiding light reflected from the sample to a displacement detection optical system described below. and a displacement detection optical system to detect minute displacements of the sample.
A photothermal displacement microscope characterized by having a configuration including a displacement signal processing circuit that converts the output obtained from the displacement detection optical system into a displacement signal.