抄録
Laser interferometers are widely utilized for the displacement measurement at nanoscale because of its inherent accuracy. Moreover, this method can keep the traceability to the definition of the meter if the wavelength or frequency is calibrated. Recently, an LD is selected as a light source because of its high power, small size, large frequency tunability and it offers direct frequency modulation through an injection current modulation. However, the long term drift of the laser frequency, typically at a rate of several megahertz per minute, must be improved before it can be applied for high accurate displacement measurements. Fortunately, molecular iodine has a broad spectrum of absorption lines from the green to the near infrared (500-900nm). Its hyperfine structure components provide a spectrum of reference frequencies for frequency stabilization of lasers. To detect the absorption signal buried in the noise, the frequency of the laser is modulated across the hyperfine lines. A sinusoidal phase (frequency) modulation technique is effective for the displacement measurement by an interferometer. In this paper, we propose the use of sinusoidal phase (frequency) modulation on a laser diode (LD) to achieve both the frequency stabilization of the LD and a displacement measurement by a homodyne interferometer.
