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: In this article, a thermal method to measure laser beam profiles was developed, where a laser beam is absorbed by a heat-resisting film and transformed into heat, and a profile of the temperature increment over the receiving film is radiometrically detected by a thermographic instrument.
Abstract: A thermal method to measure laser beam profiles has been developed. A laser beam is absorbed by a heat‐resisting film and transformed into heat. A profile of the temperature increment over the receiving film is radiometrically detected by a thermographic instrument. The method is demonstrated by one‐dimensional profile measurements of a pulsed YAG laser beam whose energy density is several J per cm2.
22 citations
Patent•
01 Apr 1992
TL;DR: In this article, a beam splitter is used to divide the laser beam into two beams, one pointing along a reference path, and the other pointing at an object to be identified as a friend or foe.
Abstract: A friend-or-foe (IFF) identification system (10) comprises a laser generator (12) for generating and transmitting a laser beam (B). A beam splitter (16) divides the laser beam into two beams. One of the beams (B1) is directed along a reference path (P). This beam is reflected back along the path by a mirror (24) positioned at the end of the path. The other laser beam (B2) is directed at an object (T) to be identified as a friend or foe. This second beam reflects off the object and the return, reflected beam is detected. The reflected beam includes a vibration signature of the object under investigation. The return beam and reference beam are processed together to correct the vibration signature of the object for arty distortions. This allows an accurate target signature to be obtained. Next, the target signature is compared against other signatures. The results of the comparison provide the IFF identification.
22 citations
Patent•
12 Jul 1999
TL;DR: In this paper, an apparatus and method for using an acousto-optic scanning laser vibrometer for measuring a dynamic parameter of micro and macro components is disclosed. But the method is based on the phase shift between the laser beam striking on the object of investigation and the beam striking the reference surface due to the difference in the optical path.
Abstract: An apparatus and method for using an acousto optic scanning laser vibrometer for measuring a dynamic parameter of micro and macro components is disclosed. A coherent source of a laser beam of single wavelength and of stabilized frequency is split into two orthogonal polarized beams. One of the beams strikes the surface of investigation and gets reflected back, and the other polarized beam impinges on the reference surface and gets reflected back. The beam reflected from the surface of investigation and the beam from the reference surface are combined, thereby causing them to interfere. At least one photo detector is positioned at the point of interference. The photo detector output signals are input to a signal processor or phase meter to obtain the dynamic parameter information. Information is provided that is based on the phase shift between the beam striking on the object of investigation and the beam striking the reference surface due to the difference in the optical path. The information provided relates to the dynamic parameters of the object under investigation.
22 citations
TL;DR: In this paper, a continuous scanning system based on a laser Doppler vibrometer (LDV) whose laser beam is driven to scan continuously over the rotor surface, in order to measure the operational deflection shapes (ODSs) in short time, with high spatial density and accuracy, appears very promising.
Abstract: In rotating machinery, variations of modal parameters with rotation speed may be extremely important in particular for very light and undamped structures, such as helicopter rotors or wind turbines. The natural frequency dependence on rotation speed is conventionally measured by varying the rotor velocity and plotting natural frequencies versus speed in the so-called Campbell diagram. However, this kind of analysis does not give any information about the vibration spatial distribution i.e. the mode shape variation with the rotation speed must be investigated with dedicated procedures. In several cases it is not possible to fully control the rotating speed of the machine and only coast-down tests can be performed. Due to the reduced inertia of rotors, the coast-down process is usually an abrupt transient and therefore an experimental technique, able to determine operational deflection shapes (ODSs) in short time, with high spatial density and accuracy, appears very promising. Moreover coast-down processes are very difficult to control, causing unsteady vibrations. Hence, a very efficient approach for the rotation control and synchronous acquisition must be developed. In this paper a continuous scanning system able to measure ODSs and natural frequencies excited during rotor coast-down is shown. The method is based on a laser Doppler vibrometer (LDV) whose laser beam is driven to scan continuously over the rotor surface, in order to measure the ODS, and to follow the rotation of the rotor itself even in coast-down. With a single measurement the ODSs can be recovered from the LDV output time history in short time and with huge data saving. This technique has been tested on a laboratory test bench, i.e. a rotating two-blade fan, and compared with a series of non-contact approaches based on LDV: traditional experimental modal analysis (EMA) results obtained under non-rotating conditions by measuring on a sequence of points on the blade surface excited by an impact hammer, continuous scanning LDV measuring the ODS of the structure excited by an impact hammer modulating the laser output, tracking laser Doppler vibrometry (TLDV) operating at different rotation speeds under stationary conditions, tracking continuous scanning laser Doppler vibrometry (TCSLDV) operating at different rotation speeds under stationary conditions. EMA and TLDV have been performed over the same grid of points sufficiently dense to have ODSs with adequate spatial resolution, it requiring long measurement time. The application of different techniques allowed us to completely characterize the tested bladed rotor and to validate the continuous scanning application to transient rotator processes.
22 citations
TL;DR: In this article, a compact I2-stabilized frequency-doubled Nd:YAG laser has been developed for a long gauge block interferometer, where a fast frequency modulation (20 kHz) is applied to the piezoelectric transducer attached on the laser crystal.
Abstract: A compact I2-stabilized frequency-doubled Nd:YAG laser has been developed for a long gauge block interferometer. The laser frequency stabilization is realized by the third-harmonic technique, where a fast frequency modulation (20 kHz) is applied to the piezoelectric transducer attached on the laser crystal. The relative uncertainty of the laser frequency has reached 3.6×10-12 for a 0.01-s averaging time. It is theoretically indicated that the phase error in the interferometric measurement due to the optical frequency modulation is sufficiently small to measure the long gauge block up to 1000 mm. Long gauge block measurement up to 1000 mm was successfully demonstrated with the developed I2-stabilized frequency-doubled Nd:YAG laser.
22 citations