Laser-diode interferometer with a photothermal modulation.

A laser-diode (LD) interferometer that uses an accurate photothermal-modulating technique is proposed. Since this technique with the photothermal method modulates only a wavelength of the LD, measurement accuracy is not affected by an intensity modulation that usually appears in the current modulation. The fundamental characteristics of this technique are investigated in detail. The new setup is tested, and its accuracy is compared with that of a previous system.