Wavelength variation measuring apparatus

A wavelength variation stabilizing apparatus comprising:

• a light source whose wavelength is controllable;
• a light divider for dividing a light beam from said light source into two light beams;
• a frequency difference imparting device for causing a frequency difference between said two light beams comprising acoustooptic elements disposed in paths of the two light beams divided by said light divider respectively;
• a geometrical length difference between optical paths imparting device for causing a geometrical length difference between optical paths of said two light beams, the geometrical length difference between optical paths caused by said geometrical length difference between optical paths imparting device being substantially constant at least during detection of any variation in the wavelength of said light source;
• a light combining device for combining said two light beams between which the frequency difference and the geometrical length difference are imparted;
• a photoelectric detector for detecting a beat signal in the combined beams of constant geometrical length difference between optical paths;
• a variation detector for detecting any variation in the wavelength of said light source by using a result of detecting of the beat signal in the combined beams of constant geometrical length difference between optical paths performed by said photoelectric detector;
• and
• feedback control means for controlling feedback to said light source on the basis of said variation detector and stabilizing the wavelength of said light source.

A correcting apparatus comprising:

• a light source;
• a light divider for dividing a light beam from said light source into two light beams;
• a frequency difference imparting device for causing a frequency difference between said two light beams;
• geometrical length difference between optical paths imparting device for causing geometrical length difference between optical paths of said two light beams, the geometrical length difference between optical paths caused by said geometrical length difference optical paths imparting device being substantially constant at least during detection of any variation in the wavelength of said light source;
• a light combining device for combining said two light beams between which the frequency difference and the geometrical length difference are imparted;
• a photoelectric detector for detecting a beat signal in part of the combined beams of constant geometrical length difference between optical paths to thereby detect any variation in the wavelength of said light source, the rest of the combined beams being directed to an object to be measured for obtaining measurement data;
• and
• variation detector for detecting any variation in the wavelength of said light source by using a result of detecting the beat signal in the combined beams of constant geometrical length difference between optical paths performed by said photoelectric detector:
• the measurement data obtained by the rest of said combined beams being corrected with a signal from a variation detector as a measurement data correction signal.

A wavelength variation detecting apparatus comprising:

• light source means;
• light dividing means for dividing a light beam from said light source means into two light beams;
• frequency difference imparting means for causing a frequency difference between said two light beams;
• geometrical length difference between optical paths imparting means for causing a geometrical length difference between optical paths of said two light beams;
• and
• light combining means for combining said two light beams between which the frequency difference and the geometrical length difference are imparted, part of said combined beams being guided to an interference optical system,
• wherein a beat signal in the rest of said combined beams which is divided from the part in an optical path between said light combining means and the interference optical system is detected to thereby detect any variation in the wavelength of said light source means.

A wavelength variation detecting method comprising:

• an illuminating step of providing an illuminating light beam from a light source;
• a light dividing step of dividing the light beam from said light source into two light beams;
• a frequency difference imparting step of causing a frequency difference between said two light beams using acoustooptic elements disposed in paths of the two light beams divided in said light dividing step, respectively;
• geometrical length difference between optical paths imparting step of causing a geometrical length difference between optical paths of said two light beams, the geometrical length difference between optical paths caused by said geometrical length difference between optical paths imparting step being substantially constant at least during detection of any variation in the wavelength of said light source;
• a light combining step of combining said two light beams between which the frequency difference and the geometrical length difference are imparted;
• and
• a photoelectric detecting step of detecting a beat signal in the combined beams of constant geometrical length difference;
• and
• a variation detection step of detecting any variation in the wavelength of said light source by using a result of detecting the beat signal in the combined beams of constant geometrical length difference between optical paths performed in said photoelectric detecting step.