JPS5853731B2 - Reflectance transmittance measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for measuring reflectance and transmittance, which are optical properties of glass and other materials.

To explain the conventional technology using an example of transmittance measurement shown in FIG. The photocurrent was converted into a photocurrent by a converter 4 and read by an ammeter 5.

In such a measurement method, since the measured reflectance and transmittance depend on the linearity and signal-to-noise ratio of the photoelectric converter 4, it is necessary to measure a weak region of light incident on the photoelectric converter 4 and the ammeter 5. was difficult.

Therefore, in the present invention, a laser device is used as the light source 1, and by pulse width modulating the laser light, light with varying apparent intensity is guided to the test object 3, and the amount of light entering the photoelectric conversion device 4 is always constant. By doing so, it is intended to expand the measurement range of low reflectance and low transmittance.

The present invention will be explained below based on the drawings.

In FIG. 2, 11 is a laser oscillation device, a laser beam 12 is split into two by a beam splitter 13, one enters a photoelectric converter 14, and the other is pulse width modulated by a modulator 15 and then optical system 16. The light enters the test object 17 via the.

The light reflected or transmitted through the test object 17 is detected by a photoelectric converter 18.

The comparator 19 uses three factors: the intensity of the laser beam 12 detected by the photoelectric converter 14, the intensity of the reflected light or transmitted light of the object 17 detected by the photoelectric converter 18, and a preset reference amount. By comparing the values, it is determined whether the illumination light 20 should be strengthened, (B) it can be left as it is, (C) it should be weakened, etc., and the command is sent to the pulse generator 21.

The beam splitter 13 and the photoelectric converter 14 are installed to ensure that the measured values are not affected by variations in the laser light output.

The pulse generator 21 generates pulses with a predetermined repetition frequency, and the pulse width changes according to a command from the comparator 19.

For example, when a signal (4) to strengthen is input, the pulse width gradually increases, and when a signal (C) to weaken is input, the pulse width gradually decreases.

22 is a modulator drive control circuit that supplies power to the modulator 15 according to a signal generated by the pulse generator 21.

In the apparatus of the present invention, as an example, the beam splitter 13
The laser beam 12 is divided into two equal parts, the repetition frequency of the pulse generator 21 is IKHz, and the test object 17 is
If the comparator 19 is set to balance with a pulse width of 1 microsecond, that is, a duty of -1/1000 in a state where The ratio to the amount of light is 1/1000.

In other words, a constant of 171,000 is set.

Next, when the test object is attached, the output light amount decreases and the ratio with the reference light amount becomes smaller than the constant 1/1000, but the pulse width of the illumination light 20 increases until it reaches an equilibrium state where this value is equal to the constant l. The light is modulated and controlled so that a constant amount of light always enters the photoelectric converter 18.

The value obtained by dividing the duty of the illumination light in this equilibrium state by the constant is the reciprocal of the reflection or transmittance of the object.

With the above settings, it is possible to measure reflection or transmittance of up to 1/1000.

In the actual device t, a constant is set taking into account the split ratio of the beam splitter 13 and the ratio of conversion efficiencies of the two photoelectric converters 14 and 18.

Furthermore, it is clear that a beam splitter is not necessary when the same amount of laser light is emitted from both ends of the laser transmitter.

As described above, according to the device of the present invention, measurement is performed with the amount of light incident on the photoelectric converter always being a constant value, so it is not affected by the linearity of the converter and has extremely low reflection or transmission. This makes it possible to measure with high accuracy down to the rate.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing a conventional technique. FIG. 2 is an explanatory diagram showing an embodiment of the present invention. 1... Light source, 3... Test object, 4...
...Photoelectric converter, 5...Ammeter, 11...
...Laser device, 15...Modulator, 17...
...Object to be tested, 18...Photoelectric converter, 19.
... Comparator, 21 ... Pulse generator, 22 ... Modulator drive control circuit, 23 ...
····display.

Claims (1)

[Claims] 1 A means for pulse-width modulating one of the two divided laser beams oscillated by a laser oscillation device based on a predetermined frequency using a modulator, and making the modulated laser beam enter the test object as incident light, and means for reflecting or transmitting the laser light from the test object. The ratio of the output light amount and the light amount of the other of the two divided laser beams is compared with a preset constant, and the modulator is controlled so that the ratio is in an equilibrium state where the values are equal, and the pulse of the incident light is A reflectance/transmittance measuring device comprising: means for varying the width; and means for calculating and displaying reflection or transmittance as the reciprocal of a value obtained by dividing the duty of the incident light pulse in the equilibrium state by the constant value.