| 摘要 |
PURPOSE:To improve S-N ratio, by executing synchronous wave detection by utilizing zero-order diffracted light, which passes an acoustic optical element without undergoing wavelength dispersion, and first-order diffracted light which undergoes the wavelength dispersion. CONSTITUTION:A beam having entered from a slit 1 is converted to parallel beams by a lens 2, single-polarized by a polarizer 3 and brought into an acoustic optical element 4. DC vaoltage and a wave, which is formed by putting AC voltage on the DC voltage at a cycle longer than the frequency, are added to an electrode 5 alternately. During the period when AC voltage is overlapped, sine wave refraction distribution is formed in the acoustic optical element 4, it becomes a kind of diffraction grid, the entered beam is bent by diffraction and received by beam-receiving unit 6 through a lens 2' and a slit 1'. On the other hand, in the case of applying only DC voltage, the entered beam goes straight and is received by a beam-receiving unit 6'. And wave of an output of the beam-receiving unit 6 is synchronously detected with an output of the beam-receiving unit 6' as a reference source. It is possible, by doing so, to measure wavelength of even a weak input beam with high accuracy. |
