JPS62197754A - Measurement of heat conductivity - Google Patents

Abstract

PURPOSE:To measure heat conductivity of an object to be measured at a high accuracy, by a method wherein a beam from a pulse laser is made incident to one end of an optical fiber and emitted from the end thereof to irradiate the object being measured and a rise in the temperature is measured. CONSTITUTION:A laser beam 2a from a pulse laser 1 is focused with a lens 3 to be incident into one end of a step index type optical fiber 4. At this point, the laser beam 2a propagates through the optical fiber 4 while being totally reflected repeatedly many times to become uniform spetially by being distributed evenly. The beam is emitted from the other end of the optical fiber 4, made parallel with a lens 5, adjusted in the beam diameter with a diaphragm to irradiate and heat the surface of the object 7 being measured, A rise in the temperature of the object 7 being measured is measured with a thermometer 8 to determine heat conductivity. This makes spatial energy distribution of a pulse laser beam uniform thereby enabling highly accurate measurement of heat conductivity.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to the spatial energy distribution of a pulsed laser beam, and relates to a thermal conductivity measuring method having an irradiation optical system formed of a pulsed laser and an optical fiber.

[Prior art and problems]

In conventional methods, a pulsed laser beam was directly guided to the object to be measured to irradiate and heat it (for example, Maglich.

Cesaryan, Pellecky (ed.) Introduction to Thermophysical Properties Measurement, Volume 1, Review of Measurement Techniques J (1984) Plenum Press, New York; Maglic, Ceza
irli-yan, edited by Pe1etsky Com
pendium of Thermopbisical
Property Measurement Meth
ods, Volume 1, 5urveyof M
easurement Techniques J +
(1984).

Plenum Press, New Yark, p.
308.312.313). However, the spatial energy distribution of the pulsed laser beam is not necessarily uniform, and as a result, the surface of the object to be measured is not heated uniformly, which poses a problem in that it reduces the measurement accuracy of thermal conductivity (for example, .

p320-326 of said document).

In view of the above points, there is a need for a thermal conductivity measurement method that can irradiate and heat an object to be measured with a pulsed laser beam having a uniform spatial energy distribution.

[Purpose of the invention]

In view of the above points, the present invention provides a novel method for measuring thermal conductivity that improves the measurement accuracy of a pulsed laser beam. The purpose is to

[Structure and operation of the invention]

This object is achieved according to the invention by focusing a pulsed laser beam into one end of an optical fiber and exiting it from the other end. When a laser beam is introduced into an optical fiber, the beam propagating through the optical fiber undergoes multiple total reflections, and as a result, the spatial energy unevenness at the time of incidence disappears and is averaged out, resulting in spatial uniformity. An extremely good beam can be obtained.

[Embodiments of the invention]

The present invention will be explained below with reference to the drawings. FIG. 1 shows an embodiment of the present invention, in which a laser beam 2a emitted from a pulsed laser 1 is focused by a lens 3 and made incident on one end of a step-index type optical fiber 4.

Since thermal conductivity measurement requires a pulsed laser with high output energy, the laser is usually oscillated in multiple modes.

At this time, even if the laser is adjusted most carefully, the spatial energy distribution of the laser beam 2a cannot be made uniform.

When a laser beam is incident on a step-index optical fiber as in this example, the beam propagating through the optical fiber undergoes multiple total reflections (as it undergoes repeated experiences, the spatial energy unevenness at the time of incidence changes). disappears,
Averaging results in a beam with very good spatial uniformity.

Laser beam 2b emitted from the other end of optical fiber 4
is converted into a parallel beam by a lens 5, and the beam diameter is adjusted by an aperture 6 as necessary to irradiate and heat the surface of the object to be measured 7. At this time, the spatial energy distribution of the laser beams 2C and 2d can be obtained with extremely good uniformity. The temperature rise on the back surface of the object to be measured 7 is measured with a thermometer 8.

〔Effect of the invention〕

As explained above, the present invention uses an optical fiber to generate a pulsed laser beam with a uniform spatial energy distribution, and irradiates and heats the surface of a thin plate-shaped object to be measured with this beam. .

As a result, the heat flowing inside the thin plate-shaped object to be measured from the front surface to the back surface can be regarded as a one-dimensional flow, and -
It is possible to improve accuracy when calculating thermal conductivity using an analytical formula assuming dimensional heat flow.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing an example of an apparatus for carrying out the method of the present invention. 1...Pulse laser, 4...Optical fiber/<-,7
...Object to be measured, 8...Thermometer. Designated agent 2t) Figure 1

Claims (1)

[Claims] A beam from a pulsed laser is focused and input into one end of an optical fiber, and the beam emitted from the other end irradiates and heats the surface of the object to be measured, and the resulting temperature rise in the object is measured. Characteristic thermal conductivity measurement method.