Laser interferometer

A laser interferometer, comprising:

• a light source configured to emit laser light;
• an optical divider configured to divide the laser light into a first optical path and a second optical path;
• an optical modulator on the first optical path;
• an oscillation circuit configured to output a reference signal and a drive signal wherein
• the optical modulator includes an oscillator that oscillates in a case where the drive signal is supplied to the oscillator,
• the optical modulator includes a container that accommodates the oscillator and the oscillation circuit,
• the optical modulator is configured to modulate the laser light by making the laser light enter the oscillator, and
• the oscillator is a signal source of the oscillation circuit;
• a photoreceptor configured to receive the laser light and output a photoreception signal, wherein the laser light is reflected by an object to be measured that is provided on the second optical path;
• and
• a demodulation circuit configured to demodulate, from the photoreception signal, a Doppler signal derived from the object to be measured, wherein
• the demodulation is based on the reference signal output from the oscillator and a modulation signal derived from the optical modulator,
• the reference signal is changed according to an angular frequency of the modulation signal,
• the modulation signal is different from the Doppler signal, and
• Iq/f≤1×10−7 is satisfied, where an amplitude value of the current applied to the oscillator that is oscillating is Iq and an oscillation frequency of the oscillator is f.