Patent ID: 7426038

Claim:
A detection apparatus comprising: a light source emitting probe light having a first wavelength and reference light having a second wavelength different from said first wavelength; a frequency shifter branching said probe light into first probe light and second probe light, and said reference light into first reference light and second reference light, and shifting frequencies of said first probe light and said first reference light or frequencies of said second probe light and said second reference light; an irradiation unit irradiating a measurement object with said first probe light and said first reference light; a superimposition unit superimposing said first probe light and said first reference light applied to said measurement object by said irradiation unit on said second probe light and said second reference light; and a phase detecting unit detecting a phase of a beat produced by superimposition of said first probe light on said second probe light on the basis of a beat produced by superimposition of said first reference light on said second reference light.