Calibration apparatus and calibrating a laser doppler vibrometer

A calibration apparatus for calibrating a laser Doppler vibrometer, the calibration apparatus comprising:

• a monodirectional frequency shifter stage in optical communication with the laser Doppler vibrometer and that:
• receives, from the laser Doppler vibrometer, primary laser light comprising a primary frequency;
• produces, from the primary laser light, frequency shifted light comprising a shifted frequency, such that the shifted frequency differs from the primary frequency;
• communicates the frequency shifted light from the monodirectional frequency shifter stage to a reflector;
• the reflector in optical communication with the monodirectional frequency shifter stage and that:
• receives frequency shifted light from the monodirectional frequency shifter stage;
• and
• reflects the frequency shifted light from the monodirectional frequency shifter stage to a beam splitter;
• and
• the beam splitter in optical communication with the monodirectional frequency shifter stage and the reflector and that:
• receives the primary laser light from the laser Doppler vibrometer;
• communicates the primary laser light to the monodirectional frequency shifter stage;
• receives the frequency shifted light from the reflector;
• and
• communicates the frequency shifted light as secondary light to the laser Doppler vibrometer, such that the laser Doppler vibrometer receives the secondary light from the beam splitter and produces a synthetic velocity shift from the secondary light.