求翻译：目前主要有的单频激光多普勒测速仪：迈克尔逊式位移干涉仪[1]，差分混频测速仪[2], 速度干涉仪[3]；外差式双频激光多普勒测速仪[4-5]是什么意思？

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Currently there are mainly of single-frequency laser Doppler Laser Speed Detector: Michael Robinson-type displacement interferometer [ 1] and a differential mixing Laser Speed Detector [ 2] [ 3] interferometers, speed, and poor-style dual frequency laser Doppler Laser Speed Detector [ 4 - 5]

At present mainly has monofrequent laser Doppler velometer: Michael abdicates type displacement interferometer [1), difference mixing velometer [2), speed interferometer [3); Heterodyne type dual-frequency laser Doppler velometer [4-5)

At present, the main existing single frequency laser Doppler velocimeter: Michelson Interferometer type displacement [1], the difference frequency mixing guns [2], velocity Interferometer [3]; type double frequency heterodyne laser Doppler velocimeter [4-5]

At present, the main existing single frequency laser Doppler velocimeter: Michelson Interferometer type displacement [1], the difference frequency mixing guns [2], velocity Interferometer [3]; type double frequency heterodyne laser Doppler velocimeter [4-5]