Method and device for measuring f-p cavity free spectral range based on characteristic absorption lines

Abstract

The invention provides a method of measuring an F-P (Fabry-Perot) cavity free spectral range based on a characteristic absorption line. A tunable narrow-linewidth diode laser wavelength scanning method is adopted to measure an F-P cavity transmittance curve and an absorption spectrum of two characteristic absorption lines at the same time; then, through counting the number of interference peaks on the F-P cavity transmittance curve in a line interval of the two characteristic absorption lines, measurement on the F-P cavity free spectral range is realized. The center frequency of the characteristic line is extremely accuracy and reaches 10<-6> cm<-1>, and is not influenced by the measurement environment and the measurement system. The precision of measuring the F-P cavity free spectral range can be effectively improved, and the FSR measurement precision can be better than 10<-6> cm<-1>. Besides, all calculation steps can be automatically processed through computer programming, and the operation is easy.

Description

technical field [0001] The invention relates to an optical precision measurement technology, in particular to a method and a device for measuring the free spectral range of an F-P cavity. Background technique [0002] Fabry-Perot etalon (referred to as F-P cavity) is an important instrument to realize multi-beam isoclinic interference. It is not only used in high-resolution spectroscopy to study the ultra-fine structure of spectral lines, but also widely used in laser wavelength stabilization, measuring length, fields such as wavelength and refractive index. Free spectral range (FSR), as an important characteristic parameter to characterize F-P cavity, needs to be accurately determined in many applications. [0003] In the prior art, the free spectral range is usually calculated according to its definition. For a parallel plane standing wave cavity, the light propagates back and forth in the cavity, and the expression of the free spectral range is as follows: [0004] FSR=...

AI Technical Summary

Problems solved by technology

However, the cavity length L and the refractive index n vary with different materials, ambient temperature, airflow, etc., and it is not easy to obtain accurate results, thus affecting the calculation results of the free spectral range

In view of this, even if the F-P cavity has been precisely calibrated at the factory, its free spectral range will change when the use environment changes, so it needs to be re-measured in many optical precision measurement experiments

[0008] At present, the measurement of the free spectral range of the F-P cavity mainly uses a spectrometer or a wavelength meter to detect the wavelength interval between the two peaks of the transmission spectrum of the F-P cavity for conversion. Due to the limited accuracy of the spectrometer or wavelength meter (about 10 -3 cm -1 ), and the scanning wavelength range is limited, so it is used to measure the free spectral range of the F-P cavity, which has the disadvantages of low sensitivity, poor precision, and small dynamic range.

In addition, high-quality spectrometers and wavelength meters are expensive, and manual interpretation of the projection spectrum peaks of the F-P cavity is required, which requires high professional skills for operators

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