Dispersion interferometer using orthogonally polarized waves

Details Dispersion interferometer using orthogonally polarized waves Dispersion interferometer using orthogonally polarized waves

1995-02-28

1997-06-24

Gonzalez, Frank

Optics: measuring and testing

By dispersed light spectroscopy

Utilizing a spectrometer

356349, 356361, G01B 902

Patent

active

056421958

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The invention relates to dispersion interferometers of the type used for measuring the dispersion part of a refractive index of media under examination by an interferometric method and can be used in the optical industry and also in the composition of diagnostic complexes of various plasma installations of the type of Tokamak, Stallarator, gas discharge lasers.


PRIOR ART

The methods of interferometry make it possible to determine a change, necessitated by media, in the optical length of a path nS (n--refractive index, S--geometric length of the path). Given the length of the object under examination, one may conclude about the refractive index of a material and vice versa for objects with a known refractive index one can register the profile of its thickness with an accuracy comparable with the wavelength of radiation. If measurements are carried out on two different wavelengths .lambda..sub.1 and .lambda..sub.2, one can determine the dispersion portion of the optical length of the path [n.sub.1 (.lambda..sub.1)-n.sub.2 (.lambda..sub.2)]S. For example, in plasma the value of (n.sub.1 -n.sub.2) is unambiguously associated with electron concentration. The common feature of interferometers is the provision of two independent optical branches. The result of interference depends on the difference of wave phases travelling along two branches and converged in an interference element. Inasmuch as the wave phase in media depends on the geometric path, polarization and radiation frequency, we can single out three types of interference circuits. In classic interferometers practised on a large scale, the radiation of a source is divided into two waves with equal frequency, which travel on different geometric paths in the branches.
Very popular are interferometers for plasma diagnostics operating simultaneously on two and more wavelengths which are constructed according to the classical circuits of the first type, say, of Mach-Zender, Michelson, to mention only a few (L. N. Pyatnitsky, S. L. Rak, V. A. Ron'kin, G. C. Yakushev "Three-frequency high-responsive laser interferometer", PTE, 1983, N 5, pp. 181-185). The difference of geometric paths is a main reason behind the defect of such circuits--high response to the vibration of optical elements. For elimination of a vibration effect, a complex of measures are taken which complicate these systems, say, use of vibration-insulating bed plates, long wave radiations (inclusive of 337 .mu.m), two-wavelength interferometers with a compensation of vibrations on a shorter wavelength (for instance, 0.63 .mu.m).
Known in the art is also a new type of interferometers called dispersion of which two branches correspond to waves with a different frequency with the same geometric path (SU--PS 864942, O OID 9/02). They display a number of substantive advantages: first, a dispersion contribution is measured therein into a refractive index (in plasma it is determined by electrons), and is not derived as a difference of two large values; second, they possess a lesser response to the spurious vibrations of optical elements.
The dispersion interferometer of this type comprises a radiation source with a frequency .omega., two non-linear optical doublers of frequency at a distance providing the arrangement of an object under examination therebetween, a light filter and a register, means all located along the optical axis.
In this device, given the illumination of an interferometer with laser radiation with a frequency .omega..sub.1, part of this radiation is converted into harmonic radiation with a frequency .omega..sub.2 =2.omega..sub.1 in the first non-linear element. Thus, the object under examination is translucent with two wavelengths of the frequency .omega..sub.1 and .omega..sub.2. When passing through the second non-linear element the frequency .omega..sub.1 is partially converted into a wave .lambda.'.sub.r with the frequency .omega..sub.2. A light filter cuts off the radiation of the fundamental frequency. At the output of the interferometer there remain two wav

REFERENCES:
patent: 5037202 (1991-08-01), Batchelder et al.
patent: 5394240 (1995-02-01), Matsumoto
Pyatnitskii, L.N., et al., "Sensitive Three-Frequency Laser Interferometer", PTE, 1983, No. 5, pp. 181-18, with translation.

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