SU1185195A1 - Apparatus for measuring absolute indicator of refraction - Google Patents

Abstract

A DEVICE FOR MEASURING THE ABSOLUTE RELIEF INDICATOR, containing an optical radiation generator and an amplitude detector optically coupled to it, the output of which is connected through an amplifier to a frequency meter that registers an absolute index of refraction. the refractive index of samples with a thickness greater than the wavelength, in the device between the optical radiation generator and the amplitude detector are introduced in series An amplitude modulator, a nonreciprocal radiation power divider, and a mirror, along the optical radiation path, the non-reciprocating power divider is optically coupled to the amplitude detector S and the control input of the amplitude modulator is connected to the amplifier output. SL /

Description

The invention relates to optical measurements and can be used to measure the absolute refractive index of optical materials / 1,

The aim of the invention is to extend the measurement range of the absolute refractive index value of samples with a thickness greater than the wavelength.

The drawing schematically shows a diagram of the proposed device.

The device consists of successively arranged oscillator 1 of optical radiation, amplitude modulator 2, and reciprocating power divider 3, mirror A, as well as amplitude detector 5, amplification 6, frequency / measure 7, and non-reciprocal dividend 3 is optically connected to amplitude detector 5, the output of the amplitude detector is connected to the input of the amplifier 6, and the output of the amplifier is connected to the input of the frequency meter 7 and the control input of the modulator 2.

The device works as follows.

In the absence of a sample to be measured, the optical radiation from the generator 1 passes through the amplitude modulator 2 and its mutual power divider 3, hits the mirror 4. Reflected from the mirror, the optical radiation is diverted by the reciprocating power divider to the amplitude detector 5. The signal from the amplitude detector 5 is amplified by weight 6 and is supplied to the control input of the amplitude modulator 2. Thus, in the circuit there is feedback for the modulating signal. To obtain stable self-oscillations modulating optical radiation, it is necessary to fulfill two conditions for the amplitude balance and the phase balance. To fulfill the amplitude balance condition, it is necessary that the gain factor of amplifier 6 is greater than the loss factor in the rest of the circuit. The phase balance is fulfilled for auto-oscillation, the period of which is equal to the time required for optical radiation to pass through the channel: amp; An effective modulator - non-reciprocal power divider - mirror - non-reciprocal power divider - amplitude detector, and depends on the optical length of this channel. In the event of

self-oscillations, their frequency is measured by a frequency meter 7 connected to the output of amplifier 6. When a measured sample is inserted into the device, which is placed between the non-reciprocating power divider 3 and the mirror 4, the optical length. The aforementioned channel changes, and consequently, the frequency of self-oscillations modulating the optical radiation. The refractive index of the sample to be measured is calculated using the formula c (fo - fi)

n 1 +

df f

where n is the refractive index j

c is the speed of light in the free

space, m / s; f - frequency of self-oscillations in from i. the absence of the sample, Hz;

f - frequency of self-oscillations at

sample availability, Hz; d - sample thickness, m. This formula is valid for samples in the form of plane-parallel plates.

The possibility of measuring the absolute refractive index of samples with a thickness greater than the wavelength of the applied optical radiation is due to the fact that the period of self-oscillations modulating the optical radiation is greater than the time required for the sample to pass.

The refractive index measurement range is determined by the optical thickness measurement range. In known devices, this range is small, its relative value is, at best, a fraction of a unit. This is due to the fact that in these devices the measurement range of the optical thickness cannot exceed the wavelength. Otherwise, ambiguity appears in the measurements,

In the invention, the measurement range of the optical thickness is determined by the wavelength (frequency f) of an auto-oscillation modulating optical radiation in amplitude. The modulation wavelength exceeds the wavelength of the optical radiation by at least two orders of magnitude. This leads to a two-fold expansion of the optical thickness measurement range and, consequently, to an expansion of the measurement range of the absolute refractive index, for example, glasses, ceramics and ferrites in millimeter and submillimeter: The second portion of the optical range.

Claims (1)

A device for measuring the absolute refractive index, comprising an optical radiation generator and an optically coupled amplitude detector, the output of which through an amplifier is connected to a frequency meter, which is a recorder of the absolute refractive index, characterized in that, in order to expand the measuring range of the absolute refractive index samples with a thickness greater than the wavelength in the device between the optical radiation generator and the amplitude detector are introduced sequentially located e along the path of the optical radiation is an amplitude modulator, an in-direct radiation power divider and a mirror, the non-reciprocal power divider being optically coupled to the amplitude detector, and the control input of the amplitude modulator connected to the output of the amplifier. SU., „1185195>