Fizeau wavemeter

The path difference between the beams 2 and 2 is As2 = (m+l)A. The interference of the reflected light produces a pattern of parallel fringes with the separation 

Az is equal to the fringe separation A, and the two fringe patterns for A and A+5A look identical, apart from the slight change of A. It is, therefore, essential to know A at least within 5A/2. This is possible from a measurement of A. With a diode array of 1024 diodes the fringe separation A can be obtained from a least-squares fit to the measured intensity distribution I(z) with a relative accuracy of 10 , which yields an absolute value of A within 10 A [4.79]. 

With a value d = 1 mm of the air gap the order of interference, m, is about 3000 at A = 500 nm. An accuracy of 10 is therefore sufficient for the unambiguous determination of m. Since the position of the interference fringes can be measured within 0.3% of the fringe separation, the wavelength A can be obtained within 0.3% of a free spectral range, which gives the accuracy A/AA 10. The preliminary value of A, deduced from the 

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The Fizeau wavemeter constructed by Snyder [4.82] can be used for pulsed and cw lasers. While its optical design is simpler than that of the sigmame-ter and the FPI wavemeter, its accuracy is slightly lower. Its basic principle is shown in Fig. 4.70b. The incident laser beam is focused by an achromatic... 

Fig. 4,70a,b. Fizeau wavemeter (a) interference at a wedge (the wedge angle 0 is greatly exagerated) (b) schematic design A, aperture as spatial filter P, parabolic mirror C, distance holder of cerodur D, diode array... 

M.B. Morris, T.J. Mclllrath, J. Snyder Fizeau wavemeter for pulsed laser wavelength measurement. Appl. Opt. 23, 3862 (1984)... 

Figure 476 Densitometer trace of the fringe pattern in a Fizeau wavemeter [185]...

The advantage of the Fizeau wavemeter is its compact design and its low price. A very elegant construction by Gardner [203, 204] is sketched in Fig. 4.77. The... 

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