Optical-path-difference compensation mechanism for acquiring wave form signal of time-domain pulsed spectroscopy apparatus

A time-domain pulsed spectroscopy apparatus comprising:

• a pulsed laser light source;
• a splitting unit configured to split pulsed laser light from the pulsed laser light source into excitation pulsed laser light and detection pulsed laser light;
• a pulsed-light emitting unit configured to emit pulsed light including wavelengths in the far-infrared wavelength region due to irradiation of the excitation pulsed laser;
• a detector configured to detect a wave form signal of the electric field intensity of reflected or transmitted pulsed light from the sample onto which the pulsed light from the pulsed-light emitting unit is radiated;
• a sample holder configured to hold the sample;
• and
• sample-unit entrance and exit optical systems configured to guide the pulsed light from the pulsed-light emitting unit to the sample and to guide to the detector pulsed light reflected from or transmitted through the sample due to the irradiation,
• wherein the time-domain pulsed spectroscopy apparatus further comprises:
• at least one optical-path-length varying unit, disposed in an incident-side optical path from the splitting unit to the pulsed-light emitting unit and/or in a detection-side optical path from the splitting unit to the detector
• wherein the optical-path-length varying unit for setting a photometric range is a reflector that is either moveable or fixed;
• and,
• said reflector includes, at the incident side of the pulsed light to the reflector, a gate member configured to pass or block the pulsed light to the reflector by blocking to add an optical path via the reflector to extend the optical path length or passing to skip the reflector to shorten the optical path length.