Showing papers on "Laser Doppler vibrometer published in 1993"

Method and apparatus for creating an image by a pulsed laser beam inside a transparent material.

Abstract: A method of creating an image inside a transparent material with the aid of a pulsed laser beam involves use of a diffraction limited Q-switched laser, in particular, a solid-state single-mode TEM00 laser; sharp focusing of the laser beam to provide an adjustable microdestruction in the material being treated; and mutual displacement of the laser beam and the material being treated after each laser shot to a next point of the image being reproduced. The microdestruction induced in the material at a pre-set point is adjustable in size by varying the actual aperture of the focusing lens and laser radiation power simultaneously. A device for carrying out said method comprises a laser 1, a defocusing lens 2 having a variable focal length, a focusing lens 4 capable of performing controlled motion along the laser beam 3 with the aid of an actuator 5, a drive 7 moving a specimen 6 made of a transparent material in a plane perpendicular to the laser beam 3, and a computer 8 guiding the process of specimen 6 treatment.

Measurement of umbo vibration in human subjects--method and possible clinical applications.

Abstract: A commercial laser doppler vibrometer (LDV) was used to evaluate umbo displacement at sound pressure levels of 60, 70, and 80 dB SPL at the tympanic membrane (TM) of six subjects. Thirty-five pure-tone test frequencies, five per octave, were tested from 140 to 19,433 Hz. A computer program (Tymptest) produced and controlled the tones as well as improved the signal-to-noise ratio of the LDV. The test took about an hour to perform and provided reproducible results in all subjects. In addition, measurement of umbo displacement using the same system was made in 15 fresh human temporal bones for comparison

Diagnostic tests using near infrared laser absorption spectroscopy

Abstract: RF modulation spectroscopy of a near infrared laser diode source is used to determine the amount of a target substance in a breath sample. In this type of modulation the laser output is modulated to produce sidebands displaced from the laser carrier by the modulation frequency. The modulated beam is passed through a gas sample which differentially absorbs the sidebands, the result of which is the conversion of some of the laser frequency modulation into amplitude modulation which is subsequently detected using a broadband photodetector. In certain tests, the target substance is a particular isotope, whose concentration is measured as an isotope ratio. In order to measure the presence of first and second isotopic species, provision is made to provide laser illumination at characteristic wavelengths for absorption lines for the first and second isotopic species of the gas. This may sometimes be accomplished using a single laser diode and scanning at least one of its operating parameters in order to achieve one of the wavelength difference. Alternatively, first and second laser diodes operating at the first and second wavelengths are used.

Method and system for scanning a laser beam for controlled distribution of laser dosage

Abstract: A system and method for distributing an output beam from a laser system on a body which provides for a uniform fluence level throughout an entire treatment region. A first structure receives the laser beam and aims it along a propagation axis. A scanner scans the propagation axis of the laser beam at a controlled scan velocity, so that the laser beam essentially continuously scans a treatment pattern on the body. The treatment pattern can consist of an essentially straight line, or a ring, or other pattern which can be easily fitted together with other patterns to fill in a treatment area. The method includes the steps of: supplying a laser beam, directing a laser beam along a propagation axis to the body, and scanning the propagation axis of the laser beam at a controlled scanned velocity, so that the laser beam essentially continuously scans the treatment pattern on the body.

Laser beam generator

Abstract: A laser beam generator (13) includes first and second mirrors (14R, 16R), a laser light source (11), a laser medium (15), a non-linear optical crystal element (16) and a birefringent element (14). The laser light source generates a pumping light beam. The laser medium (15), arranged between the first and second mirrors (14R, 16R) is irradiated with the pumping light beam via one of the mirrors (14R) to generate a fundamental laser beam based on the pumping light beam. The non-linear optical crystal element (16) is arranged between the first and second mirrors to generate a second harmonic laser beam under the type II phase matching as the fundamental laser beam from the laser medium (15) is passed through it in resonant oscillation. The birefringent element (14) has its one surface at a pumping light beam inlet side coated with a high reflectance coating (14R) and has its opposite surface parallel to it with a nonreflective coating (14T). The birefringent element (14) is set so that its optical axis is inclined at a predetermined azimuth angle with respect to the crystal axis of the non-linear optical crystal element (16). The surface of the birefringent element (14) coated with a high reflectance coating (14R) constitutes one of the first or second mirrors.

Laser beam irradiating apparatus enabling uniform laser annealing

Abstract: A laser beam irradiating apparatus is capable of laser annealing with high precision and uniform over the entire surface of a sample. Luminous flux of the laser beam output from a laser source is expanded by a beam expander. The power of the laser beam which has passed through the beam expander is adjusted by a half-wave plate of synthetic quarts and a polarizing prism of synthetic quarts. The laser beam emitted from polarizing prism is guided to a prescribed position by mirrors, and swung in the direction of the X-axis by an X-axis rotation mirror. The laser beam reflected from X-axis rotation mirror has its diameter reduced by a f-θ lens to have a prescribed beam spot diameter on the surface of a silicon wafer, and laser beam scanning is carried out at a constant speed. Since half-wave plate and the polarizing prism are formed of synthetic quarts, thermal deformation of optical components caused by continuous irradiation of laser beam can be suppressed, beam profile of the laser beam can be stabilized, therefore highly uniform and highly precise laser annealing becomes possible.

Laser synchrotron source (LSS)

Abstract: The laser synchrotron source (LSS) utilizes a high peak power or high average power laser to generate within a vacuum chamber a laser beam travelling in one direction to interact with an electron beam traveling in an opposite direction in order to generate high-power x-rays. A ring resonator formed by a plurality of mirrors directs the laser beam in a closed loop to impact with the electron beam to produce x-rays. Concave mirrors in the ring resonator focus the laser beam upon the point where the laser beam interacts with the electron beam to intensify the laser energy at that point. When a radio frequency linear accelerator (rf linac) is used to produce the electron beam, x-rays having a short pulse length are generated. When a betatron is used as an electron source, x-rays having a long pulse length are generated.

Ultrasonic bonding apparatus and quality monitoring method

Abstract: An ultrasonic bonding apparatus comprises an ultrasonic wave controller, a bonding system including a bonding head, a laser oscillator, a laser optics, a vibration monitoring system including a vibrometer, and a mechanism for feeding a result of monitoring back to a bonding condition.

Electronic speckle pattern interferometry using diode lase stroboscopic illumination

Abstract: An electronic speckle pattern interferometer (ESPI) using stroboscopic illumination from a diode laser, and its application in vibration measurement, are described. Diode lasers are readily frequency (FM) and power modulated (AM) via control of their injection current; they are inexpensive and compatible with the single-mode optical fibres used in the described system. However, their modest peak power output demands the use of high-duty-cycle pulses, so that it was necessary to synchronize the illumination with the turning points of the vibration. This was achieved by operating the ESPI system in conjunction with a laser vibrometer. Injection-current-induced FM of diode lasers is non-uniform for modulation frequencies less than about 10 MHz, and to achieve successful stroboscopic illumination an electronic equalization stage was included to shape the current pulse, and hence compensate for the non-uniform FM.

Laser Doppler velocimetry using a bulk optic Michelson interferometer: A student laboratory experiment

Abstract: The Doppler frequency of reflected light from a moving mirror is measured using a Michelson interferometer and a low cost spectrum analyzer. The experimental data for the Doppler frequency are in agreement with the calculated theoretical values with a standard percent error of 0.54%. The concept of optical mixing of a phase‐modulated signal with the Doppler signal is presented, with a derivation of the resulting detected signal power, using the small phase modulation amplitude approximation. An experiment is described using laser Doppler velocimetry to heterodyne the Doppler signal with an acoustic wave. The experiment provides a good illustration of the Doppler effect, spectral analysis, and principles of optical mixing and interferometry in an advanced undergraduate laboratory.

Optical information reading method for reducing laser noise using a semiconductor laser and a driving device for the semiconductor laser

Abstract: A method for optically reading recorded information by radiating laser light emitted from a semiconductor laser which oscillates in a single longitudinal mode to an information recording medium and by detecting laser light reflected from a recording face of the information recording medium is disclosed. In the method, the optical frequency of the laser light is modulated in order that the modulated optical frequency is a periodic function dependent on time, and the absolute value of a time differential coefficient R (Hz/s) of the periodic function, a spectral line width δ ν (Hz) of the laser light, and a time period τ (s) from the time when the laser light is emitted to the time when the laser light reflected from the recording face of the information recording medium reaches the semiconductor laser satisfy the condition of R≧δ ν/τ. The periodic function varies to have a sawtooth waveform or a triangular waveform.

Increasing the frequency stability of single‐frequency lasers

Abstract: We have developed an improved technique to increase the stability of single‐frequency lasers by employing a scanning Fabry–Perot interferometer and a stabilized helium neon laser. Our instrument surpasses earlier devices in several key areas. The laser frequency can now be stabilized while scanned across its inherent single‐frequency tuning range. The frequency stability is long term with an increased frequency correction rate of nearly 500 Hz. The laser frequency can be scanned repeatedly with a repetition accuracy equal to the frequency stability. Also, the electronics permit the laser frequency to be swept externally while synchronized with other instruments. Our stabilizer reduced the frequency drift of a commercial ring dye laser to ±1 MHz relative to the reference laser.

Distributed laser Doppler velocimeter

Abstract: Classical LDV techniques permit the recovering of the flow profile at the expense of the movement of projection and recovery optics. This operation limits the performances of the LDV and extends the measurement time. The aim of this communication is to present a novel monobeam distributed laser Doppler velocimeter (DLDV) which permits the continuous recovery of the flow velocity at any point belonging to the light beam, without moving the collimating optics. The DLDV applies the low-coherence multiplexing technique to a backscattering reference-beam LDV scheme. The DLDV uses a very-short coherence source (a superluminescent diode) which feeds an unbalanced interferometer. The sensing arm of the interferometer is launched in the flow while the remote reference arm permits the user to interrogate different flow volumes. The scheme has been implemented by all-fiber components. Preliminary measurements were given on a laboratory hydraulic circuit. The DLDV can be used as a conventional LDV, to measure with high accuracy a flow velocity component in a point of the duct, or in a distributed mode, to recover the flow velocity profile along a duct cross-section. Profiles of the flow were recovered at different average velocity and the first results confirm the exceptional capabilities of the novel instrument.

Two-Channel Laser Vibrometer Techniques for Vibrational Intensity Measurements: Part 1—Flexural Intensity

Abstract: A laser technique which measures vibrational energy flow (intensity) via propagating bending waves is described. A pair of scanning laser beams from a two-channel laser vibrometer is used to provide a nonintrusive measurement of the intensity at various points on a vibrating beam. Results are shown to compare well with those of two additional techniques. These techniques, used for validation, employ a single laser beam and can only be used at resonance frequencies in beams or rods. The two-channel laser technique described can be applied to two-dimensional intensity measurements, is not limited to single frequency excitation, and has an inherent capability to facilitate phase error elimination via a photodetector switching technique which is also described.

Measuring apparatus with optically conjugate radiation fulcrum and irradiated area

Abstract: A laser beam from a light source having a laser beam emitting portion and a laser output mirror is applied to an irradiation area in a flow cell by an irradiation optical system. Scattered light and fluorescence radiated by particles flowing through the flow cell are detected by a detector. The vicinity of the laser output mirror which is the fulcrum of the fluctuation of the pointing of the laser beam and the irradiation area are made optically substantially conjugate with each other, and even if the pointing of the laser beam fluctuates, measurement can be effected accurately without being affected thereby.

Method for controlling the amplitude of an optical signal

Abstract: An amplitude control scheme for a high bit rate digital optical transmitter is disclosed. The data to be transmitted by the laser is pulse-width modulated by a low frequency signal. The pulse-width modulated signal is applied to the laser via a laser driver and to a mark density reference generator. The magnitude of the low frequency components from the mark density reference generator is a signal indicative of the desired amplitude of the laser light pulses. A back-face photodiode converts a portion of the laser light into an electrical signal, the magnitude of the low frequency portion thereof being a signal indicative of the actual amplitude of the laser light pulses. The actual amplitude of the laser light pulses is computed to the desired amplitude and the laser driver output amplitude may then adjusted to compensate for variations in the laser performance.

Method of magneto-optical recording

Abstract: After a laser beam of a high-level laser beam is applied to a multilayer magneto-optical recording medium to record information thereon, a laser beam of a laser power lower than the laser power of a reading laser beam is applied or substantially no laser beam is applied for a period of time τ0. If one channel clock period or the period in which the high-level laser beam is of the second laser power is applied is τw, then the ratio R=(τ0 /τw)×100 is selected to be in the range from 15 to 70%.

Laser transmitter for light wave (fiber optic) communication espectially of AM modulated CATV signals having means . . . against damage

Abstract: A laser transmitter utilizes a laser diode which is biased to its stimulated (laser) emission mode of operation by the application of current from a source of one or more operating voltages The failure of any of these voltages and over temperature conditions of the laser are detected by an optical AND gate which switches the operating voltage off when any one of them is absent The temperature of the laser is also detected and applied to one of the optos in the chain of the AND gate such that an over temperature condition also results in the switching off of the operating voltage and shut down of the laser The temperature detection is by way of a circuit having hysteresis such that the optical AND gate is not enabled until the temperature the laser decreases below the initial cut off temperature Operating current for biasing the laser for laser emission is applied gradually over a period from one to five seconds by connecting the switched operating voltage source to the laser through a slow start circuit The laser operating current and also the level of the modulating signal (an RF modulating signal carrying a plurality of CATV channels) is applied to the laser through a switching circuit which cuts off the modulating signal when either the current to the laser or the modulating signal level is below predetermined limits

Co2 laser beam machine

Abstract: PURPOSE:To enable piercing at a high speed with high accuracy by reflecting a laser beam by a pair of rotationally moving mirrors and providing optical parts for focusing the beams to a prescribed plane. CONSTITUTION:The galvanomirrors 5, 6 are so rotated and positioned as to irradiate the prescribed piercing position with the laser beam according to the processing data previously inputted to a control unit 16. A light emission trigger signal is sent from this control unit 16 to a CO2 laser oscillator 1 and the laser beam 2 is outputted at a prescribed laser output and width. The laser beam 2 is reflected by the mirrors 3, 4, is polarized in a prescribed direction by the galvanomirrors 5, 6 and is focused by ftheta, by which a sheet 9 is irradiated and subjected piercing. The surface of the sheet 9 is nearly perpendicularly irradiated with the converging part of the laser beam 1. The sheet 9 is pierced with the piercing hole perpendicularly to the processing surface thereof with good accuracy.

Direction sensitive laser Doppler velocimeter using the optical frequency shift of two stabilized laser diodes

Abstract: The commonly used techniques for directional discrimination in velocity measurements involve a frequency shift of the LDA light beams which are focussed into the measuring volume. The paper presents a new technique for the generation of a frequency shift be using the optical frequency difference of two current and temperature stabilized monomode laser diodes. By focussing the output beams of the two frequency stabilized laser diodes into the measuring volume it is possible (1) to save the commonly required components for the beam splitting and frequency shifting and (2) to double the light intensity in the measuring volume. It will be shown that using conventional laser diodes, the influence of frequency shift fluctuations and large band widths on the measuring information in the carrier frequency signal can be eliminated by appropriate heterodyne signal processing techniques. The concept of the described new frequency shift technique will be discussed critically and first experimental results will be presented.

Inspection/adjustment method and apparatus for laser beam output optical unit and laser scanning optical system

Abstract: There is disclosed a laser beam output optical unit adjustment method and apparatus, which can perform inspection and adjustment of a laser beam unit and a laser scanning optical system including this unit used in a laser beam printer within a short period of time. The laser irradiation position is roughly adjusted using a wide-field position detector, and focus rough adjustment is then performed using a narrow-field position detector. Thereafter, fine adjustment of the irradiation position and focus fine adjustment are performed using the narrow-field position detector. An image enhancement tube capable of a high-speed gate operation is arranged in a laser scanning region, and instantaneously takes a beam spot during laser scanning. An image processing devices analyzes the taken spot image, and a calculation unit calculates various data.

Method and apparatus for detecting laser light having a plurality of pulse integrator and automatic gain control circuits

Abstract: A laser light detector is provided which can be used to detect pulsed laser light that is produced by a rotating laser light source on a construction job site. The laser light detector provides an easily-read display which is indicative of the present level or elevation of the laser light detector with respect to the plane of rotating laser light. The laser light detector has a very large dynamic range, while maintaining a very good signal-to-noise ratio, and can, therefore, be used at both short and long distances from the rotating laser light source. The laser light detector is not dependent upon the energy level received of laser light, or by the spot size of laser light as it reaches the light detectors. Multiple discrete steps of elevation indication are provided, which can easily be increased to a larger number of discrete steps, if so desired. The laser light detector is available with several options, including dead band adjustment, normal or offset on-grade displaying, and averaging.

Spectrogram processing of laser vibration data

Abstract: Laser vibration sensing has traditionally relied on the use of limiters and frequency modulation (FM) discriminators to process frequency modulated laser radar returns. The performance of the traditional FM discriminator approach can be limited by laser radar target characteristics and motion (speckle noise) and laser temporal coherence. In this paper we examine a novel laser vibration signal processor, a spectrogram processor, and compare its performance with the traditional limiter/FM discriminator signal processor used to process laser radar vibration measurements. The two processes are also compared using some laser radar measurement data.

Laser beam irradiating device

Abstract: PURPOSE:To eliminate failures in the machining through the irradiation by the laser beam of the energy intensity distribution except the prescribed value. CONSTITUTION:The irradiation optical path of the converged laser beam 51a onto a work 52 is provided with a measuring member 64 to measure the energy intensity distribution of this laser beam 51a, and a shut-off means 65 which transmits the laser beam if the laser beam 51a to transmits this measuring member 64 is of the prescribed energy intensity distribution type, and on the other hand, shuts off the laser beam if it is not of the prescribed energy intensity distribution type.

Process-optimizing adaptive optics for the beam delivery of high-power CO2 lasers

Abstract: SUMMARYA newly developed opto-electronical system component for laser material processing was presented. It is a bending mirror,the surface of which can be deformed to approximately spherical. The focal length is negative and variable from infiniteto -2 metres. Depending on the optics position with regard to laser source and focussing optics there are different effectson the characteristic quantities of the focused laser beam. Locating it far away from the condensing optics mainly the spotsize is influenced while in a position very close to the focussing optics essentially the image length can be varied.Different applications were discussed and proofed by testing.In equipment with flying optics varying beam path length can be compensated for. Interference effects in the laser beam's delivery caused e. g. by thermal lensing can be corrected, too. A virtually mass-free adjustment of the focal position enhances the accessibility to at complex workpiece structures. Testpieces with stiffening corrugations and small radii could be welded.High frequencies in the focus shift lead to new laser technologies such as "laser beam sawing". Although there is a lot offundamental work left, first results with a non-adapted gas flow pointed to a high and innovative potential.

Laser beam machining method and laser beam machine

Abstract: PURPOSE:To provide the laser beam machining method and laser beam machine capable of always obtaining proper power density required for machining even when a cross-sectional shape of a laser beam is extended or contracted. CONSTITUTION:The laser beam 7 outputted from a laser beam oscillator 1 is changed into the elliptical cross-sectional shape by cylindrical surface lens 2a and 2b of a beam diameter converter 2. The distance change between the two cylindrical surface lens by movement of a movable table 20 is detected by a distance detector 21 and this detected signal is inputted to an arithmetic circuit 10. In the arithmetic circuit 10, the change of size of a spot 8 condenced on material 5 to be machined is calculated, a power density distribution is regulated so that the power density in a region of a specified area of the spot 8 exceeds a specified value corresponding to this change and the laser beam of this power density distribution is outputted from the laser beam oscillator 1.