An interference imaging device includes a light interference generator that includes: a light wave splitter configured to reflect a part of incident light and to allow a remaining part of the incident light to pass through; a phase modulator configured to modulate a phase of incident light that has passed through the light wave splitter; and a reflector configured to reflect the phase-modulated incident light from the phase modulator so that the reflected, phase-modulated incident light overlaps with incident light that has been reflected by the light wave splitter.

An interference imaging device includes a light interference generator that includes: a light wave splitter configured to reflect a part of incident light and to allow a remaining part of the incident light to pass through; a phase modulator configured to modulate a phase of incident light that has passed through the light wave splitter; and a reflector configured to reflect the phase-modulated incident light from the phase modulator so that the reflected, phase-modulated incident light overlaps with incident light that has been reflected by the light wave splitter.

A substrate holder for use with an interferometer comprises a first and second support each comprising a bearing land and a bearing base arranged to form a bearing pocket and a gas inlet fluidly coupled to the bearing pocket. The first support and the second support are positioned relative to one another such that the first bearing pocket is opposed to the second bearing pocket thereby forming a measurement cavity between the first support and the second support. At least one of the first support and the second support comprises reference optics through which one or more interferometric or optical measurements can be taken. Gas supplied to the first bearing pocket and gas supplied to the second bearing pocket form an air bearing in the measurement cavity for supporting a substrate in the measurement cavity without contact between the substrate, the first support, and the second support.

In a general aspect, a wavelength of light is measured. In some aspects, a wavelength measurement system includes an interferometer, a camera system, a sensor and a control system. The interferometer includes two reflective surfaces and a transmission medium between the two reflective surfaces. The interferometer is configured to receive an optical signal from a laser and produce an interferogram in response. The camera system is configured to receive the interferogram from the interferometer and generate interferogram data in response. The interferogram data represents the interferogram received from the interferometer. The sensor is configured to sense an environmental parameter of the transmission medium and generate sensor data in response. The control system is configured to perform operations including, receiving the interferogram data from the camera system and the sensor data from the sensor; and computing a wavelength of the laser based on the interferogram data and the sensor data.

Heterodyne spectrally controlled interferometry is performed by combining a delay line in Twyman-Green configuration with a Fizeau interferometer. By splitting a white-light beam in the delay line and introducing a time delay in one of the resulting beams, the delay line produces a recombined output beam with a sinusoidally modulated spectrum. By introducing a frequency shift in one of the beams in the delay line, the output beam is also continuously phase shifted in the spectral domain in a time-varying fashion, as required for heterodyne SCI.