Showing papers on "Laser Doppler vibrometer published in 1990"

Laser beam deflection as a probe of laser ablation of materials

Abstract: Probe beam deflection is used for identification of the laser fluence threshold for excimer laser photoablation of various materials. The beam deflection signal due to an acoustic wave and a thermal wave are both distorted as the excimer laser beam fluence is raised through the ablation threshold.

Scanning laser Doppler Technique for velocity profile sensing on a moving surface.

Abstract: A scanning laser Doppler technique based on Chebyshev demodulation has been developed for the rapid measurement of spatially distributed velocity profiles. Scan frequencies up to 100 Hz can be used over scan lengths up to 270 mm. The Doppler signals are processed in the conventional manner using a frequency counter. The analog velocity output from the counter is post-processed to obtain the velocity profile. The Chebyshev demodulation post-processing technique for processing the velocity signals from solid surfaces has been introduced. The data processing technique directly yields the spatial velocity distribution in approximate functional form through frequency domain analysis of the scanning LDV velocity output. Results from a rotating disk setup are presented to illustrate the concept.

A scanning laser doppler vibrometer for modal testing

Abstract: Accelerometers are widely used to sense structural response in modal testing. The mass loading and local effects due to accelerometers are not always negligible. The laser Doppler velocimeter/vibrometer (LDV) is a noncontact optical sensing tool for accurately measuring point velocities. The noncontact nature of the instrument makes it particularly attractive for use on lightweight structures where measurement interaction must be minimized. Real-time scanning LDV's have recently been introduced to measure fluid flow velocity profiles rapidly. In this paper, the development of a real-time scanning LDV for structural applications is described. The instrument can be used to simultaneously measure the velocity response at a series of locations on a vibrating structure. Standard modal analysis techniques can then be applied to extract the usual modal data, e.g., natural frequencies, damping and mode shapes. The special case of beam vibration is considered in this paper though the technique can be readily extended to generic planar measurements. The measurement technique has been validated through modal testing of a simple beam structure. Comparisons between theoretical and LDV measured mode shapes and natural frequencies are presented. 20 refs.

Narrow-band oscillation excimer laser

Abstract: A narrow-band oscillation excimer laser employing a diffraction grating as a wavelength selecting element, which is particularly suited for a light source of a reduction type projection aligner. The grating used in the narrow-band oscillation excimer laser of the invention is so disposed that the direction of grating lines is nearly perpendicular to the direction of laser discharge. When a beam expander is used to expand laser beam falling on the beam expander is so disposed that the direction of beam expansion is nearly perpendicular to that of discharge of the laser. Further, when an aperture is to be used in the optical resonator, the aperture is placed so that the longitudinal direction may be parallel to the direction of laser discharge. Moreover, the front mirror of the optical resonator is a cylindrical one, whose mechanical axis is in parallel with the direction of laser discharge. This makes it possible to provide a narrow-band oscillation excimer laser having very high efficiency and excellent durability.

Integrated semiconductor diode laser and photodiode structure

Abstract: An integrated semiconductor structure with optically coupled laser diode (11) and photodiode 12A, both devices having etched, vertical facets (16A, 21). The photodiode has a spatially non-uniform sensitivity profile with respect to the incident light beam (18A) emitted by the laser. This is due to the varying distance from the laser facet and/or to variations in the angle of incidence and results in photocurrents produced by the photodiode that depend on the intensity distribution of the light beam. The spatially non-uniform sensitivity profile allows the measurement of the far-field intensity distribution of the laser and thus on-wafer screening of lasers with respect to their mode stability.

Laser alignment servo method and apparatus

Abstract: A servo alignment method and apparatus for maintaining laser beam alignment. An operating parameter of the laser (such as output beam power) is measured, and error signals are generated from the measured operating parameter signal for controlling the laser beam alignment. In one class of embodiments, modulation signals are supplied to an intra-cavity component of a laser system to modulate the beam path. The beam path may be modulated by reciprocating a laser resonator mirror about a mirror axis or two substantially orthogonal mirror axes. In the latter case, the mirror may be vibrated about the axes either alternately (first about one axis and then about the other) or simultaneously. In embodiments in which an intra-cavity component is modulated, the laser operating parameter is measured during such modulation, the measured operating parameter signal is demodulated (preferably by multiplication in a mixer with a selected frequency component of the modulation signal currently being asserted, and error signals are generated from the demodulated signal for controlling the laser beam alignment.

Medical laser apparatus, high powered red laser used in same, and laser resonator with non-linear output

Abstract: A laser system generates suitable laser power for use in photodynamic therapy, and particularly photodynamic therapy using dyes which undergo desired photodynamic reactions at 659 mm, ie, Purpurin The laser system generates a red output power of greater than 4 watts For the therapeutic applications, a means for delivering the red beam to therapeutic sites is provided The laser system provides for a frequency doubled solid-state laser system in which the non-linear birefringent crystal used to provide frequency doubling is mounted adjacent a flat mirror whereby losses due to walkoff of the beam caused by the crystal are minimized The laser resonant cavity defined by one flat and one other mirror, which may be stabilized by means, such as thermal lensing in the solid-state gain medium, inside the cavity A frequency doubled Nd:YAG rod in such cavity tuned to 1319 microns with a KTP frequency doubling crystal for generates an output beam at 0659 microns via type II phase matching required for photodynamic therapy in conjunction with a suitable PDT compound or dye

Pel placement correction in the scan dimension of a multiple beam laser scanning system

Abstract: This is an electronic scheme for correcting mechanical misalignment and electrical delays from laser beam to laser beam in the scan direction of a multiple beam laser scanning system for use in an electrophotographic machine. The position at which a reference beam is turned on is sensed and adjusted to a desired position. Thereafter, the positions at which non-reference laser beams are turned on are sensed and adjusted to the desired position. In one enbodiment, the energization of laser beams is positioned at the trailing edge of the second element of a photodector. In a second embodiment, the point of full laser energy is matched, beam to beam, at the junction of the same two elements in a CCD array. Programmable delay lines are used to obtain sub-pel resolution.

Diode laser frequency doubling using nonlinear crystal resonator with electronic resonance locking

Abstract: A semiconductor laser apparatus comprises a DC power supply coupled with an RF source which generates a low-amplitude RF current which is injected into a diode laser source An optical beam shaping system processes the laser beam and directs it to a nonlinear resonator having a plurality of longitudinal resonator frequencies with a fundamental spatial mode The nonlinear resonator uses a phase-matched, second harmonic generation (SHG) process to generate a second laser beam by frequency doubling the central carrier frequency of the diode laser source, and further reflects a portion of the incident laser beam to an electronic resonance locking system The electronic resonance locking system has a photodetector to receive the reflected portion of the incident beam from the resonator and generates an RF signal arising from the difference in phase shifts or amplitude losses experienced by the RF sidebands An RF mixer receives the RF signal from the photodetector and an input from the RF source to generate an error signal as a feedback signal which is supplied to the diode laser source for tuning the laser injection current

In vivo comparison of a twin wavelength laser Doppler flowmeter using He—Ne and laser diode sources

Abstract: This paper reports the results of a preliminary in vivo investigation in which laser Doppler blood-flow measurements were made in a variety of tissues in the anaesthetized rat using a twin wavelength laser Doppler system. The aim was to assess whether there was any detectable difference in the depth response of the laser Doppler system to blood-flow in skin, muscle and brain tissue using red light (633 nm) from a He—Ne laser source and near infrared (NIR) light (780 nm) from a semiconductor diode laser source. The results show that under normalized conditions, the flow signals obtained from the near infrared laser Doppler system is consistently larger than that recorded from the red He—Ne laser Doppler system. This suggests that laser Doppler flowmetry systems based on NIR laser sources sample larger volumes of tissue than those based on red He—Ne lasers.

Laser projection type display unit

Abstract: A laser projection type display unit. A light modulator is provided between a laser light source and a galvanometer scanner. By cutting off the laser beam or modulating the amplitude of the laser beam by means of the light modulator, independent point groups can be displayed.

A new, high sensitivity laser vibrometer

Abstract: This paper introduces a new design of laser vibrometer which allows high sensitivity, noncontact measurement of normal-to-surface target motion. The design includes use of a retro-reflective tape covered PZT-element to remove the sign ambiguity in surface velocity, which is inherent in the form of Doppler detection used in laser vibrometers. Utilization of this element offers the potential for a compact, cost effective design, suitable for portable, on-site use in engineering situations.

Slider-disk interactions during the load-unload process

Abstract: The issue of slider-disk contact during the loading process is investigated. The effects of initial altitude, pitch, and roll are studied by using the LDV (laser Doppler vibrometer). The relative displacement of the slider with respect to the disk and the change of pitch and roll during the loading process are obtained for the 3380-type slider and the thin-film disk. The effect of the loading location of the disk is studied. LDV and AE (acoustic emission) measurements are carried out to detect possible slider-disk contacts during the loading process. The AE signal shows some bursts which have the slider ringing-frequency components. But by comparing the AE signal with the LDV results before and after lubricating the gap between the pivot and suspension, the sources of the AE bursts are found to be the normal contact and slip between the pivot and suspension. It is therefore concluded that carrying out the load-unload process of the positive pressure slider using a mechanism which actuates the middle part of the suspension is a suitable solution to high stiction and friction problems that can develop in the contact-start-stop process. >

Cutting apparatus for an optical disc

Abstract: A cutting apparatus is provided, in which a recording laser beam from a laser light source is ON/OFF-modulated by an optical modulating device on the basis of a square output signal in which a video FM wave signal is pulse width modulated by an audio FM wave signal thereby to form exposure pits on a master disc. This cutting apparatus includes a photodetector for receiving one portion of the recording laser beam irradiated on the master disc from the laser light source or a photodetector for receiving a reflected light of the recording laser beam irradiated on the master disc from the laser light source and which is reflected on the master disc. A detected output signal from the photodetector is supplied through a low-pass filter to a control circuit which controls an intensity of an output laser beam from the laser light source, and an offset of a source system line is adjusted so that a secondary higher harmonic component of a main carrier in the detected output from the photodetector is minimized.

Power laser generator with control of the direction of emission of the output beam

Abstract: This invention relates to power laser generators in which it is possible to control the angular direction of output laser beams. The generator according to the present invention is characterized by the fact that it successively comprises on the same optical axis of propagation, a pilot laser beam generator to generate a laser beam wavelength, a controllable deflector, a beam separator, a laser amplifying medium with the wavelength of the pilot beam, and a phase conjugation nonlinear mirror. The laser generator is applicable, in particular, to missile guidance systems or in telemetry systems.

Tracking Dynamics of Read/Write Head Suspensions in High-Performance Small Form Factor Rigid Disk Drives

Abstract: Recording density of rigid disk drives is related to both linear and track density. High linear density requires submicron recording spacing which is made possible by using a gas-lubricated slider bearing to support the read/write transducer. This critical component has inspired much reseach effort in the past, both in industry and in academia. On the other hand, a major limitation in increasing the track density is the structural resonance of the suspension which connects the slider bearing to the actuator arm. In this paper, a nonintrusive measurement technique using a Laser Doppler Vibrometer is utilized to measure the submicron suspension vibration

Method of stabilizing the laser beam and apparatus utilizing the same

Abstract: According to the invention, a probe laser beam having a wavelength which is different from that of the laser beam emitted from a laser apparatus is introduced into the apparatus to adjust the optical device so that any fluctuations in the probe laser beam passing through or reflected from the optical device may be eliminated. Therefore, any fluctuations in output power and/or the oscillation wavelength of the narrowed bandwidth laser beam emitted from the apparatus can be directly detected and the laser apparatus can be so controlled as to ensure a stabilized operation under an optimum condition.

Method of evaluating quality of a laser beam in a laser processing machine

Abstract: A method of evaluating quality of a laser beam output of an X-Y-Z movement laser processing head of beam generator by detecting an instantaneous profile of the beam by means of dynamical laser beam analyzer, calculating values of beam stability parameter of the beam profiles, each value of the beam stability parameter corresponding to one of the laser beam profiles, comparing the beam profiles detected and adjusting mirror orientation in the generator and calculating a standard deviation of the stability parameters and adjusting condition in supplying a laser gas to the generator.

Role of disk surface roughness on slider flying height and air-bearing frequency

Abstract: The flying heights and air-bearing frequencies during the transition from flying to sliding were measured as a function of disk speed for thin-film disks with various roughness magnitudes using a multichannel laser interferometer and a laser-Doppler vibrometer. An acoustic emission transducer was also employed to detect head-disk contact. No significant differences in the flying heights or air-bearing frequencies were observed for different disk roughnesses at the tested speeds, but the landing speeds for the smoother disks were lower. It was found that the landing speed of a slider does not correlate with RMS surface roughness, but is more a function of asperity peak heights. There was no observed dependence of the air-bearing frequency on surface roughness at any speed. It is concluded that the effect of the surface roughness on the flying height and air-bearing frequencies is minimal, and the presence of isolated asperities affects the slider landing speed. >

Laser beam profiler having a multimode laser diode interferometer

Abstract: A laser beam profiler having a movable member on which is mounted a means adapted to be moved through a laser beam for measuring the profile of the laser beam. The profiler comprises an interferometer which uses a multimode diode laser to generate a reference laser beam and a distance measuring laser beam. A retro-reflector is rigidly attached to the movable member and varies the path length of the distance measuring laser beam as the movable member is moved. A photodetector responsive to the reference laser beam and the distance measuring laser beam as said movable member is moved provides a frequency modulated output signal, said output signal having an envelope, the amplitude of which varies as a function of Δl, where Δl is the difference in the path lengths of said reference and said distance measuring laser beams, said interferometer, including said movable member, being so arranged that the amplitude of said envelope of said output signal is maximum when Δl is zero.

Laser doppler frequency control

Abstract: A pulse Doppler, laser radar as described which includes master laser whose output Fo is shifted in frequency by dF(t) during its amplification. The dF(t) frequency shift is compensated by providing a modulator which modulates the master laser output frequency Fo with a local oscillator signal F1. A first mixer is provided which combines the shifted master laser frequency signal and the local oscillator modulated, master laser output so as to eliminate the master laser frequency Fo from the combined signals. A second mixer is provided for combining the reflected, Doppler shifted laser signal with the local oscillator modulated, master laser output signal Fo +F1 to eliminate the master laser output frequency Fo from the combined signal. Additional detection circuitry is provided to determine the difference in frequencies of the combined signals from the first and second mixers so as to isolate the Doppler shift signal from the amplifier-induced shift dF(t). An additional frequency control subsystem for the master laser is also described which employs an absorption cell in the feedback loop.

Optical disk cutting apparatus

Abstract: An optical disk cutting apparatus comprises an exposure optical system for expanding an exposure laser beam and for modulating the exposure laser beam in response to a signal to be recorded, and a focus servo optical system for expanding a focus servo laser beam and for detecting a reflected beam from a master recording disk through a polarizing means, in which one of the exposure and focus-servo optical systems the laser beam of which has a wave length longer than that of the other one includes a focusing lens provided in a stage preceding the objective lens for focusing the expanded laser beam Therefore, it is possible to make the respective focal positions of the exposure laser beam and the focus servo laser beam be substantially the same and to obtain a small aberration by means of the difference in refractive index between laser beams

Laser beam controller for surveying equipment

Abstract: A laser beam controller for surveying equipment comprises a laser beam irradiation unit for irradiating a target with a laser beam, an observation unit for observing the laser beam reflected from the target and a light quantity controlling unit for controlling the quantity of the laser beam projected to the target. The laser beam controller is capable of constantly controlling the quantity of the laser beam incident on the observation optical system within a range which allows the observation of a laser beam spot and which has no harmful influence on the observer's eyes.

Miniature laser vibrometer system with multifunction integrated optic circuit

Abstract: A miniature laser vibrometer system (LVS) that uses a proton-exchanged LiNbO/sub 3/ multifunctional integrated optic circuit for signal processing is discussed. The system uses a pigtailed 0.83- mu m laser diode as the source and common-path interferometry to provide a phase-insensitive fiber-optic probe for monitoring moving or vibrating parts. The LVS provides a 55-dB signal-to-noise ratio for 3-kHz bandwidth, even when monitoring parts with relatively low (1%) reflectivity. The optical components and all electronics are housed in an 11.5-cm*10.5-cm*4.2-cm package which operates from a +or-15-V, 300-mA supply. >

Complementary two-dimensional laser Doppler velocimeter with an optical fiber probe

Abstract: Optical probing and interferometric sensing techniques have great advantages of non-loading, high resolution and wide dynamic range for motion measurement of a solid object. For this purpose, laser Doppler velocimeter (LDV) is widely utilized. However, optical measurement of two dimensional (2D) motion is a hard problem for a conventional LDV, because the instrument has a big frame size and heavy wight, and requires stable measurement environment such as an optical bench or a rigid base. In this paper, we discuss a newly proposed 2D LDV with a compact remote sensing probe. Laser light is bidirectionally transmitted via two optical fibers from a base unit to the probe head. The system is designed to measure a specific solid object that moves in 2D plane such as an optical pickup head equipped in an optical data storage system. As testing of the system, 1D displacement, velocity and acceleration of a moving membrane of a loudspeaker and 2D motion of a moving optical pickup actuator were successfully measured.

A laser power detector built up by application of thick-film technology

Abstract: A structure for a laser power detector appropriate for realization by thick-film technology has been developed. The incident laser radiation causes a heat flow in a metal plate where the resultant temperature differences, detected by thick-film Pt sensor elements, act as a measure of the laser power. The sensitivity of the sensor has been calculated and experimentally determined. By means of a theoretical model, it can be shown that the indicated laser power is independent of the radial intensity distribution of the laser beam.

Solid body laser - comprising microcrystal laser resonator and separate mirror

Abstract: Solid body laser (I) pumped by diodes has longitudinally and transversally determined unimodel operation, whose solid body is optically excited and the pump light is longitudinally focussed into the resonator mode. The novelty is that a microcrystal laser resonator is made of a laser crystal (10), e.g. Nd:YAG crystal and a separate mirror (11). The laser crystal (10) has flat ground and polished surfaces (f2,f3) and a piezoelectric foil (12) of strong electostriction determines the laser wavelength between the laser crystal (10) and mirror (11). ADVANTAGE - The laser can be easily made and has a frequency modulation 'in single frequency operation' in the GHz range.

Laser beam harmonics generator and light exposing device

Abstract: A laser beam harmonics generator comprises a laser beam source for emitting a laser beam, a harmonics generator for generating harmonics of the laser beam in response to the irradiation of the laser beam, and a displacement unit for relatively displacing the harmonics generator and the laser beam substantially perpendicular to a light path of the laser beam.

Method and apparatus for determining the position and diameter of the focal point of a laser beam

Abstract: The present invention is a process and apparatus for determining the position and diameter of the focal point of a laser beam, specifically for use in material processing with a heavy-duty laser beam. In a process for determining the position and diameter of the focal point of a laser beam, specifically a heavy-duty laser beam, a rotationally symmetric reflector which reproduces a laser beam on a focal line is introduced in the path of rays of a focused laser beam. Reflected on the reflector, the laser beam is captured by way of at least one sensor which is fixedly coordinated with the reflector in the focal line, while the focal plane, the lateral position of the focal point and the diameter of the focal point are then determined by way of measured values captured in the sensor, with the sensor being shifted relative to the focusing optics of the laser beam or relative to the reflector. The output intensity of the laser is reduced to a point where the laser can be safely and unequivocally measured with the aid of sensors.