JPH04315120A - Light source for microscope - Google Patents

Abstract

PURPOSE:To obtain a sharp image having no speckle noise by using laser light whose interference is reduced by superposing a sine wave, etc., of high frequency on a DC input to a laser. CONSTITUTION:For the measurement of a fine shape on a disk 9 which is rotated by a motor 8 at a high speed, a semiconductor laser 1 emits light, which is reflected by a half-mirror 4 and focused on the disk 9 through an objective 5. Its image is photographed by a video camera 6 and observed on a monitor 7. A synchronizing circuit 10 extracts a synchronizing signal from the rotation of the motor 8 so as to obtain a still image on the disk 9. A delay circuit 11 obtains signal which is a constant time delayed behind the synchronizing signal so as to observe an optional point on the disk 9. Then an RF superposing circuit 2 obtains an RF output which is inputted as an input signal to the semiconductor laser 1. Further, the RF-superposed light from the semiconductor laser 1 is passed through an optical fiber or aspherical lens, etc., to disorder the phase of the laser light.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light source used in a microscope, and particularly to a light source suitable for photographing a subject moving at high speed.

0002

2. Description of the Related Art Conventionally, a strobe light has been used to photograph a subject moving at high speed using a microscope. In particular, when a strobe light is applied to an object that is moving periodically, and the period of the object's movement matches the period of the pulsed light, the object appears to be at rest. Furthermore, if there is a difference between the two, the image will be observed as a slow motion image that is slower than the actual movement. When this strobe light is used as a light source for a microscope, it is possible to observe high-speed changes in minute objects such as the rotation of a motor or the movement of a domain wall.

0003

[Problems to be Solved by the Invention] With the recent progress in electronic equipment, there has been an increasing need to observe objects that change at extremely high speeds, such as from several MHz to several GHz. However, strobes store electric charge in a capacitor and emit light, so it is difficult to emit light periodically for less than 1 μs. In other words, when the light emission period becomes faster, the amount of light decreases because the charge cannot be accumulated sufficiently, and if a high-power light source is used to increase the amount of light,
The problem was that large spark noise was generated, which had a serious negative effect on the surrounding circuitry.

Further, a laser microscope using a laser as a light source uses confocal optics to avoid speckle noise caused by interference of laser light. Although this method reduces speckle noise, it cannot perform high-speed surface measurements because the light is scanned using an acousto-optic device or the like. Among laser light sources,
Semiconductor lasers are compatible with high-frequency rectangular wave drive of 1 MHz or higher, and are suitable light sources for observing rapidly changing objects as still images. As mentioned above, speckle noise, which is a mottled black and white pattern, occurs due to the temporal and spatial coherence of the laser light.
Unable to measure object. This is caused by interference between optical systems, dust, or surface roughness of the measurement object.
This is an essential problem unique to laser light.

[0005]

[Means for Solving the Problems] In order to solve the above problems, the light source for a microscope of the present invention uses a laser beam whose coherence is reduced by superimposing a high frequency sine wave or the like on the DC input to the laser. It is characterized by:

[0006]

[Operation] In the present invention, since the spectrum has sidebands due to the above-described configuration, the coherence of the laser beam is significantly reduced, and a clear image without speckle noise can be obtained.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A light source for a microscope according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows an example of the configuration of a measuring device using a light source for a microscope according to an embodiment of the present invention. (Figure 2) is (
FIG. 2 is a diagram showing signal waveforms of main parts of FIG. 1). (Fig. 1), 1 is a semiconductor laser, 2 is an RF superimposition circuit, 3 is a pulse generator, 4 is a half mirror, 5 is an objective lens, 6
1 is a video camera, 7 is a monitor, 8 is a motor, 9 is a disk rotated by the motor, 10 is a synchronization circuit, and 11 is a delay circuit. In FIG. 2, (a) is the motor synchronization signal output, (b) is the delay circuit output, (c) is the pulse generator output, and (d) is the RF superimposition circuit output.

The semiconductor laser 1 has a wavelength of 780 nm.
, with an output of 40 mW was used. The semiconductor laser to be used may be selected from a blue laser to an infrared laser with an appropriate wavelength and output depending on the wavelength characteristics of the video camera used and the object to be observed. Gas lasers and the like are not suitable because the spectrum does not expand due to RF superimposition and the transmission is unstable. The RF superimposition circuit is a circuit that can superimpose an 800 MHz sine wave on a rectangular wave pulse. The RF frequency may be higher than the frequency of the rectangular wave, and 100 MHz to 10 GHz is suitable. The video camera 6 was used because it is dangerous to measure semiconductor laser light with the naked eye. Motor 8 is 45 per minute
A disk 9 with a diameter of 12.5 cm was attached to the device rotating at 00 rpm.

In order to measure minute shapes on a disk 9 that is rotated at high speed by a motor 8, a semiconductor laser 1 emits light, is reflected by a half mirror 4, and is focused onto the disk by an objective lens 5. The image is photographed with a video camera 6 and observed on a monitor 7. In order to obtain a still image on the disk, a synchronization signal (FIG. 2a) is extracted from the rotation of the motor using a synchronization circuit 10. Then, in order to observe an arbitrary point on the disk 9 using the delay circuit 11, a delayed signal (FIG. 2b) which is delayed by Δt from the motor synchronization signal is obtained. Then, the pulse width t1, which is the light emission time for obtaining a still image, is determined by the pulse generator 3, and a shaped output signal (FIG. 2c) is obtained. A DC bias may be applied to the output. In this example, 100n
The luminescence time was set to s. Then, the RF superimposition circuit 2 obtains an RF output (FIG. 2d) which becomes an input signal to the semiconductor laser. In the present invention, the RF frequency is 800 MHz. As a result, laser emission with widened sidebands can be obtained. Normally, the half-width of a semiconductor laser is less than 0.5 nm, but R
By applying F superimposition, it can be expanded to about 5 nm. This reduced coherence in terms of frequency, making it possible to obtain a surface image with less speckle noise. With conventional strobe methods, it is not possible to set such short pulse widths; if the pulse width is long, the image will blur and become unclear.

Furthermore, in order to reduce coherence,
Spatial modulation can be further applied by scanning the optical axis of the RF-superimposed light emitted from the semiconductor laser using an acousto-optic element (A0 element), a rotating half mirror, a rotating prism, or the like. Thereby, speckle noise can be further reduced.

Furthermore, the phase of the laser beam can be disturbed by passing the RF-superimposed light emitted from the semiconductor laser through an optical fiber or an aspherical lens. That is, phase modulation can be applied to laser light. This method also makes it possible to further reduce speckle noise.

Furthermore, spatial modulation using an acousto-optic element or the like and phase modulation using an optical fiber or the like may be used together.

The narrower the pulse width of the semiconductor laser, the clearer the image, but if it is too narrow, a sufficient amount of light cannot be obtained. Although it depends on the rate of change of the object, the pulse width is preferably 10 μs or less, preferably 1 μs or less. If it is longer than this, the image will become blurred. Further, the reciprocal of the multiplexed RF frequency determines the half-width of the semiconductor laser. If it is too low, the coherence cannot be reduced sufficiently, so 100MH
z or higher, preferably 800 MHz or higher.

Although an example in which a sine wave is superimposed on a rectangular wave pulse has been described, it goes without saying that it is also effective to use a triangular wave, a sine square wave, etc. to reduce the coherence of the laser beam.

[0016] Above, a method for obtaining a microscopic image of a rapidly rotating object by RF superimposition using a semiconductor laser has been described, but the present invention is also useful for observing minute and high-speed phenomena such as movement of domain walls. Needless to say, it is used.

[0017]

As described in detail above, by using the microscope light source of the present invention, it becomes possible to observe the high-speed motion of minute objects, and the microscope light source has extremely high industrial utility value.

[Brief explanation of drawings]

[Figure 1] Configuration diagram of a measuring device using a laser light source for a microscope

[Figure 2] Diagram showing signal waveforms (a) Motor synchronous signal output (b) Delay circuit output (c) Pulse generator output (d) RF superimposition circuit output

[Explanation of symbols]

1 Semiconductor laser 2 RF superimposition circuit 3 Pulse generator 4 Half mirror 5 Objective lens 6 Video camera 7 Monitor 8 Motor 9 Disc rotated by a motor 10 Synchronous circuit 11 Delay circuit

Claims (5)

[Claims] 1. A light source for a microscope, characterized in that it uses a laser beam with reduced coherence. 2. The light source for a microscope according to claim 1, wherein the laser coherence is reduced by frequency multiplexing the input voltage to the semiconductor laser. 3. The light source for a microscope according to claim 2, wherein the light emitted from the semiconductor laser is spatially modulated by an acousto-optic element. 4. The light source for a microscope according to claim 2, wherein the light emitted from the semiconductor laser is phase-modulated by passing through an optical element having a transmittance such as an optical fiber or an aspherical lens. 5. The light source for a microscope according to claim 2, wherein the pulse width of the semiconductor laser is 10 μs or less, and the high frequency to be multiplexed is 100 MHz or more.