Controlled Fabry-Perot Wavemeter

A can be determined from the ring diameters Dp and the excess e, provided the integer order mg is known, which means that A must already be known, at least within one half of a free spectral range (Sect.4.3). 

The device is calibrated with different lines from a CW dye laser which are simultaneously measured with the travelling Michelson waveme-ter (see above). This calibration allows  

The whole measuring cycle is controlled by a computer and for pulsed lasers one pulse (with an energy of 5/iJ) is sufficient to initiate the device while for CW lasers a few /iW input power are sufficient. The arrays are read out by the computer and the signals can be displayed on a screen. Such signals for the arrays D1-D4 are shown in Fig.4.68. 

Since the optical distances n-dj of the FPI depend critically on temperature and pressure all FPI must be kept in a temperature-stabilized pressure-tight box. Furthermore, a stabilized HeNe laser can be used to control long-term drift of the FPI [4.73]. 

With a free spectral range of 8u = GHz the uncertainty of calibration and the determination of an unknown wavelength are both about 10 MHz. This gives an absolute uncertainty of less than 20 MHz. For the optical frequency u = 6 10 Hz the relatice accuracy is then Au/u 3-10 . 

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A. Fischer, H. Kullmer, W. Demtrdder Computer-controlled Fabry-Perot-wavemeter. Opt. Commun. 39, 277 (1981)... 

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