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.

Near-IR retinal laser Doppler velocimetry and flowmetry: new delivery and detection techniques

Abstract: In laser Doppler velocimetry and flowmetry of the human ocular fundus, near infrared diode lasers, coupled with avalanche photodiode detectors, offer much improved signal-to-noise ratio compared to He–Ne laser delivery and photomultiplier tube detection. The increased signal-to-noise ratio is achieved through increased retinal irradiance and better quantum efficiency of the avalanche photodiode in the near infrared. Furthermore, the small size of the diode lasers allows delivery of two individually steerable beams for simultaneous measurements in different parts of the fundus. Applications are given as illustrations of the capabilities of the system: retinal laser Doppler velocimetry in humans without need for pupil dilatation and optic nerve head laser Doppler flowmetry in the cat using flicker as a stimulus to induce blood flow changes.

Complete model to simulate the thermal defocusing of a laser beam focused in water

Abstract: Reference LOA-ARTICLE-1996-009doi:10.1117/1.600995View record in Web of Science Record created on 2009-01-20, modified on 2017-05-10

Measurement of the velocity inside an all-fiber DBR laser by self-mixing technique

Abstract: The self-mixing interference for optical velocity sensing is experimentally investigated in an all-fiber configuration distributed Bragg reflector laser. Simultaneously, theory model of self-mixing interference laser Doppler velocimeter based on quasi-analytical method. The experimental results show Doppler shift frequency is linearly proportional to the value of the velocity which agrees well with theory analysis. The results preserve an enough signal-to-noise ratio around 40 dB in the range from 39.3–317.0 mm/s (measurement range depending on bandwidth of circuit) for velocity measurement. Additionally, the cutoff circuit is used in our system to get a stable Doppler signal and reduces the error rate to 0.136 % in practical measurement.

Young's Modulus Measurements in Standard IC CMOS Processes Using MEMS Test Structures

Abstract: This letter1 presents a method to measure the Young's moduli of individual thin-film layers in a commercial integrated circuit (IC) foundry process. The method is based on measuring the resonance frequency of an array of micromachined cantilevers and using the presented optimization analysis to determine the elastic modulus of each layer. Arrays of cantilever test structures were fabricated in a commercial CMOS IC process and were released using XeF2 as a postprocessing etch. A piezoelectric transducer placed under the test chip was used to excite the cantilevers to resonance, and the resonance frequency was measured using a laser Doppler vibrometer. It is reported that excellent agreement for values of Young's modulus is observed for cantilevers between 200 and 400 mum in length, with average standard deviation being 4.07 GPa.

Enhanced resolution in two-photon imaging using a TM(01) laser beam at a dielectric interface.

Abstract: We have experimentally demonstrated that the resolution of a commercial two-photon microscope is improved using a TM01 laser beam. With a water immersion objective having a 1.2 NA, the measured point- spread function has an area of 0.15λ2. We used a plane interface between dielectrics instead of an annular aperture to increase the relative contribution of the longitudinal field of the TM01 laser beam. The results are in agreement with the vectorial diffraction theory established by Richards and Wolf [Proc. R. Soc. Lond. A253, 358 (1959)]. The TM01 laser beam was produced with a quadrant of half-wave plates. We have also used the same mode converter to generate a TE01 laser beam with a zero at the beam center.