Doppler velocimeter and apparatus using the same

An apparatus for measuring a flowing fine particle, comprising:

• means for permitting a fluid including the fine particle to flow;
• a light source for producing a light beam;
• a diffraction grating on which said light beam is incident and which produces .+-.nth-order diffracted lights at an angle of outgoing intersection conforming to a wavelength of said light beam;
• an optical system for making said .+-.nth-order diffracted lights enter so as to intersect with each other at a flow position of the fine particle at an angle substantially equal to said angle of outgoing intersection and converging said .+-.nth-order diffracted lights at the intersection position, said optical system having a lens system disposed in an optical path between said light source and said diffraction grating and for acting so that said light beam is converged, said lens system acting so that said light beam is incident on said diffraction grating in a non-focused state and said .+-.-nth-order diffracted lights are incident on the flow of the fine particle in a focused state;
• and
• detection means for detecting a scattered light subjected to Doppler shift produced from the fine particle to which the .+-.nth-order diffracted lights are radiated.

A Doppler velocimeter for detecting a movement information of an object, comprising:

• a light source for producing a light beam;
• a diffraction grating on which said light beam is incident and which produces diffracted light to be radiated onto said object;
• optical components for making said diffracted light enter at a position of the object;
• a lens system disposed in an optical path between said light source and said diffraction grating and for acting so that said light beam is converged, said lens system acting so the said light beam is incident on said diffraction grating in a non-focused state and said diffracted light is incident on the object in a focused state;
• and
• detection means for detecting a scattered light subjected to Doppler shift produced from the object to which the diffracted light is radiated and for producing a detection signal according to the detecting,
• wherein said diffraction grating and said optical components are arranged so as to prevent a frequency change of the detection signal caused by wavelength change of said light beam.