Laser Doppler vibrometer

About: Laser Doppler vibrometer is a research topic. Over the lifetime, 6319 publications have been published within this topic receiving 76068 citations.

Apparatus for direct display of an image on the retina of the eye using a scanning laser

Abstract: A direct viewing picture image display apparatus displays a good picture image with a small amount of light and low power consumption using a laser beam without producing speckle noises. The display apparatus comprises a light source for emitting a laser beam, an optical modulating system for optically modulating the laser beam from the light source in response to a video signal, a scanning system for horizontally and vertically scanning the modulated laser beam from the scanning signal in response to a scanning signal, and a projecting optical system for projecting the scanned laser beam from the scanning system to form an image of the laser beam on the retina of an eye of an observer. Depth information is provided to the laser beam at a suitable stage after optical modulation by the optical modulating system so that a stereoscopic image is displayed.

Laser Doppler detection systems for gas velocity measurement.

Abstract: The velocity of gas flow has been remotely measured using a technique which involves the coherent detection of scattered laser radiation from small particles suspended in the fluid utilizing the doppler effect. Suitable instrumentation for the study of wind tunnel type and atmospheric flows are described. Mainly for reasons of spatial resolution, a function of the laser wavelength, the wind tunnel system utilizes an argon laser operating at 0.5 micro. The relaxed spatial resolution requirement of atmospheric applications allows the use of a carbon dioxide laser, which has superior performance at a wavelength of 10.6 micro, a deduction made from signal-to-noise ratio considerations. Theoretical design considerations are given which consider Mie scattering predictions, two-phase flow effects, photomixing fundamentals, laser selection, spatial resolution, and spectral broadening effects. Preliminary experimental investigations using the instrumentation are detailed. The velocity profile of the flow field generated by a 1.27-cm diam subsonic jet was investigated, and the result compared favorably with a hot wire investigation conducted in the same jet. Measurements of wind velocity at a range of 50 m have also shown the considerable promise of the atmospheric system.

Injection laser characteristics due to reflected optical power

Abstract: Fluctuations in injection laser output intensity and spectrum caused by light reflected from an optical system are investigated theoretically and experimentally. The theoretical analysis is accomplished by applying the semiclassical theory to an injection laser, and introducing an optical feedback term. It is shown that light reflected from a near-field region causes power deviation and an oscillating wavelength shift. It is also shown that reflected light from a far-field region changes laser light spectrum and introduces frequency noise components in laser output power.

Laser vibrometer based on optical-feedback-induced frequency modulation of a single-mode laser diode

Abstract: We describe a sensitive and inexpensive vibrometer based on optical feedback by diffuse scattering to a single-mode diode laser. Fluctuations in the diode laser’s operating frequency that are due to scattered light from a vibrating surface are used to detect the amplitude and frequency of surface vibrations. An additional physical vibration of the laser provides an absolute amplitude calibration. The fundamental bandwidth is determined by the laser response time of roughly 10−9 s. A noise floor of 0.23 nm/Hz1/2 at 30 kHz with 5 × 10−5 of the incident light returning is demonstrated. This instrument provides an inexpensive and sensitive method of noncontact measurement in solid materials with low or uneven reflectivity. It can be used as a vibration or velocity sensor.