Topic
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.
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TL;DR: An industrial laser Doppler velocimeter has been developed for accurately measuring the velocity and length of moving surfaces and provides a large depth of field, high SNR, and large dynamic range making it very suitable to industrial process control applications.
Abstract: An industrial laser Doppler velocimeter has been developed for accurately measuring the velocity and length of moving surfaces The instrument’s advanced optical and electronic design provides a large depth of field, high SNR, and large dynamic range making it very suitable to industrial process control applications
94 citations
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TL;DR: The possibility of imaging the distribution of the moving red blood cell concentration is demonstrated, a first step toward laser Doppler imaging without scanning parts, leading to a much faster imaging procedure than with existing mechanical laser doppler perfusion imagers.
Abstract: We utilized a complimentary metal oxide semiconductor video camera for fast f low imaging with the laser Doppler technique. A single sensor is used for both observation of the area of interest and measurements of the interference signal caused by dynamic light scattering from moving particles inside scattering objects. In particular, we demonstrate the possibility of imaging the distribution of the moving red blood cell concentration. This is a first step toward laser Doppler imaging without scanning parts, leading to a much faster imaging procedure than with existing mechanical laser Doppler perfusion imagers.
93 citations
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TL;DR: In this paper, the BaO molecules are excited to the (v, 1') level whenever the laser wavelength coincides with an allowed v"i"-+v'i" transition in the A-X band system.
Abstract: passes through the reaction zone. As the wavelength of the dye laser is scanned, the BaO molecules are excited to the (v', 1') level whenever the laser wavelength coincides with an allowed v"i"-+v'i' transition in the A-X band system. The resulting fluorescence emitted at right angles to the laser beam is detected by a fast-response photomultiplier. The laser pulse triggers a boxcar integrator (Princeton Applied Research or Keithley Instruments) whose electronic gate (window) is maintained open from the time of the laser pulse to 2-5 times the BaO A state lifetime. This analog device permits us to average the signals resulting from many laser pulses. The scattered light from the laser beam is rejected either with a sharp cutoff Corning filter or by delaying by typically 20 nsec the opening of the electronic gate. The BaO fluorescence rate versus laser wavelength is shown in Fig.
93 citations
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TL;DR: The results suggest that the propagation of surface waves promotes the encoding of spectrally complex vibrations as the entire neural population is exposed to essentially the same stimulus.
Abstract: Because tactile perception relies on the response of large populations of receptors distributed across the skin, we seek to characterize how a mechanical deformation of the skin at one location affects the skin at another. To this end, we introduce a novel non-contact method to characterize the surface waves produced in the skin under a variety of stimulation conditions. Specifically, we deliver vibrations to the fingertip using a vibratory actuator and measure, using a laser Doppler vibrometer, the surface waves at different distances from the locus of stimulation. First, we show that a vibration applied to the fingertip travels at least the length of the finger and that the rate at which it decays is dependent on stimulus frequency. Furthermore, the resonant frequency of the skin matches the frequency at which a subpopulation of afferents, namely Pacinian afferents, is most sensitive. We show that this skin resonance can lead to a two-fold increase in the strength of the response of a simulated afferent population. Second, the rate at which vibrations propagate across the skin is dependent on the stimulus frequency and plateaus at 7 m/s. The resulting delay in neural activation across locations does not substantially blur the temporal patterning in simulated populations of afferents for frequencies less than 200 Hz, which has important implications about how vibratory frequency is encoded in the responses of somatosensory neurons. Third, we show that, despite the dependence of decay rate and propagation speed on frequency, the waveform of a complex vibration is well preserved as it travels across the skin. Our results suggest, then, that the propagation of surface waves promotes the encoding of spectrally complex vibrations as the entire neural population is exposed to essentially the same stimulus. We also discuss the implications of our results for biomechanical models of the skin.
93 citations
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TL;DR: It is shown that a stretched-pulse mode-locked fiber laser produces a welldefined frequency comb, providing a compact source of frequency combs and allowing comb-based optical frequency metrology to be extended into the 1.55 microm region.
Abstract: We show that a stretched-pulse mode-locked fiber laser produces a well-defined frequency comb, providing a compact source of frequency combs and allowing comb-based optical frequency metrology to be extended into the 1.55 μm region. This is achieved by comparing the frequency doubled output of the fiber laser to that of a mode-locked Ti:Sapphire laser, after the two lasers are synchronized. The offset frequency of the fiber laser frequency comb is found to be highly sensitive to the pump power, which enables the implementation of a feedback loop to control the offset frequency. The resulting RMS frequency jitter of the heterodyne beat signal is 355 kHz (0.5 Hz – 102 kHz BW) for this initial demonstration.
92 citations