Laser interferometric system for displacement measurement. A heterodyne laser interferometer with detection electronics has been developed for. A new type of twowavelength interferometer for the measurement of absolute distance is described. Pdf we describe a simple heterodyne laser interferometer that has subnanometer. Modeling and analysis of phase fluctuation in a high.
Laser heterodyne interferometric signal processing method. A few aspects of the heterodyne interferometer make it superior to the homodyne interferometer. Scanning heterodyne laser interferometer for phasesensitive. Development of a heterodyne laser interferometer for very small.
By adjusting the local oscillator frequency correctly, the beat. A basic michelson laser interferometer for the undergraduate. Acoustic second harmonic generation in solids is difficult to measure and often requires careful sample preparation. An advantage of the heterodyne interferometer is the potential for smaller non linearity in the quadrature pair. Introduction heterodyne manywavelength interferometry laser 1. Scanning heterodyne laser interferometer for phase. A digital heterodyne laser interferometer for studying. A twomode laser is not suitable for heterodyne method interferometer, because the difference between f1 and f2 is usually. In this paper, a heterodyne interferometer modified to measure acoustic fundamental and second harmonics is presented. To measure length with a laser interferometer the fringes are counted. To permit concurrent morphological studies and to allow precise control of the measurement location and angle, the interferometer is integrated with a laser. The heterodyne laser interferometer system consists of a hene laser head, a beam splitter, a polarization beam splitter, photodetectors, a moving mirror, and a fixed mirror. Picometer laser interferometry is an essential tool for ultraprecision measurements in frontier scientific research and advanced manufacturing. Based on the reference signal, four intervals with.
A basic michelson laser interferometer for the undergraduate teaching laboratory demonstrating picometer sensitivity kenneth g. A novel phase measurement method composed of the risingedge locked signal processing and the digital frequency mixing is proposed for laser heterodyne interferometer. There are three sources of errors of quadrature detector signals that affect the displacement measurement error. Analog processing based vibration measurement technique using. Currently, the setup allows detection of vibration amplitudes down to. Optical heterodyne detection is a method of extracting information encoded as modulation of the phase, frequency or both of electromagnetic radiation in the wavelength band of visible or infrared light. Figure 1 shows a heterodyne laser system where the beat laser beam before entering the interferometer is proportional to the next signal as a function of the difference in frequency and phase of the two beams that are perpendicular as shown in. Heterodyne interferometry using two wavelengths for dimensional.
The light signal is compared with standard or reference light from a local oscillator lo that would have a fixed offset in frequency and phase from the signal if the latter carried null. The light output from a heine laser a 632 nm enters the bragg cell. We describe a balanced heterodyne detection method for a sagnac interferometer that uses a polarizationdependent beam splitter. Twowavelength laser diode interferometer with a time. Neural networkbased laser interferometer compensation for. Polarizationbased balanced heterodyne detection method in a. We describe a scanning heterodyne interferometer for imaging surface vibrations with a wide frequency range, with current electronics, up to 6 ghz.
Pdf simple heterodyne laser interferometer with subnanometer. The risingedge locked signal processing, which employs a high frequency clock signal to lock the risingedges of the reference and measurement signals, not only can improve the steepness of the risingedge, but also can. Laser heterodyne interference signal processing method based on phase shift of reference signal. The integer fringe counting method based on overflow judgment and compensation can realize longtime and correct integer number measurement. The phase measurement method is based on crosscorrelation. This invention concerns a heterodyne interferometer for measuring the amplitude of vibration of a vibrating object. Signal processing for laser heterodyne interferometer is a key technique to realize nanometer measurement accuracy. It is shown that the output of an ideal heterodyne interferometer does not contain any even harmonics of a single. The reflected beam is used as the reference signal after passing through a. Fpgabased signal processing of a heterodyne interferometer. Odd harmonics, however, are produced in calculable amounts. Since the displacement information is carried on an ac signal rather than a dc signal, it is less sensitive to laser power fluctuations, ambient light, and various other noise affecting dc measurements.
A dualheterodyne laser interferometer for simultaneous. Without loss of generality, t sp can be set to include all analogue and digital delays occurring from modulation through to processing. This technique can be applied to a phase meter for measuring dynamic phase. In order to eliminate the influence of jitter in measurement signals on combination of integer and fraction fringe counting, the reference. In order to test the phase measurements in the tjii heterodyne interferometer co2, 10. Optical mixing errors in a fibercoupled heterodyne. The laser is ran at the sampling heterodyne frequency and then passed through a running counter that counts up to the full length of a prn code, 32768 bytes. Signal processing method of phase correction for laser.
To recover object motion, the reflected light is made to interfere with a reference beam of artificially altered frequency, producing a beating signal. The phase stability was good, with no visible fluctuations observed during the course of the experiment. Remote laser interferometer with pseudoheterodyne signal processing 1. The llrf4 board we are using was developed for the sns low level rf system2. Nov 27, 2000 remote laser interferometer with pseudo heterodyne signal processing 1. The detected heterodyne signal is arranged to be shot noise limited. Recording depth of the heterodyne laser in terferometer for cochlear vibration measurement. The system consists of an optical interferometer, a signal processing board, and a. Phase extraction for laser interferometry in space leibniz. As shown in figure 1, a beam from a doublefrequency laser containing two orthogonal linear polarization components e1 and e2 with a slight frequency difference applied to beat frequency is split into two beams by a nonpolarizing beam splitter bs. Pdf signal processing method of phase correction for laser.
Precision displacement measurement by active laser heterodyne interferometry yijyh lin and ciling pan we demonstrate an active laser heterodyne interferometer which can automatically compensate environmental disturbances and is capable of precision displacement measurement. To this end, various techniques can be implemented such as optical resonant cavity readout, or homodyne and heterodyne laser interferometry, which are discussed further in section 3 the optical readout of the test mass dynamics is not a ected by external electromagnetic disturbances, which. In this paper, we present a dualheterodyne laser interferometer for simultaneously measuring linear and angular displacements with resolutions of picometer and nanoradian, respectively. A cw double sideband suppressed carrier dsbsc signal is added onto the rf signal as a common mode. For each of the n constituent interferometers present, p n is the sum of the optical powers of the two arms forming the constituent interferometer, v n is the mutual. The signal and the local oscillator are orthogonally polarized components of a single laser beam, permitting the detection of the signal by subtraction of two photocurrents produced in appropriate polarization. Each laser transmits a prn code at the running heterodyne frequency to the far satellite where it is received, backreflected, and transmitted back to its source. Laser heterodyne interference signal processing method. Pdf laser heterodyne interferometric signal processing. The main aim of this investigation was heterodyne detection of a weak laser light scattered from a. Novel phase measurement technique of the heterodyne laser interferometer rev. In this section a method for quantifying the heterodyne interferometer measurement uncertainty and its influence on the overall calibration uncertainty is. Signal error detection and correction of quadrature detectors. Figure 1 shows the heterodyne laser interferometer seismic system.
These two heams 20 and return between the interferometer each mirror two times. Heterodyne interferometry with a frequency comb the. The heterodyne interferometer used to test the dpd system. Laser heterodyne interferometric signal processing method based on rising edge locking with high frequency clock. The spacebased gravitational wave detector lisa laser interferometer space. The block diagram of an interferometer working according to the homodyne method. It compares a far laser beam to its own local signal onboard. Detection of acoustic second harmonics in solids using a. Simple digital phasemeasuring algorithm for lownoise heterodyne interferometry. The reference beam and the measurement beam are then aligned into one beam in the. A novel signal processing method of movement direction identification and phase correction is presented for laser heterodyne interferometry. Alaserinterferometer fortheundergraduateteachinglaboratory.
The invention is particularly useful for measuring the amplitude of vibrations of objects having reflectivities below about 0. A twofrequency hene laser head emits two orthogonal linear polarized light components with the slightly different frequencies. A digital heterodyne laser interferometer for studying cochlear mechanics. In the typical superhet, the incoming radio frequency signal from the antenna is mixed heterodyned with a signal from a local oscillator lo to produce a lower fixed frequency signal called the intermediate. Recording depth and signal competition in heterodyne. Improved signal processing method for heterodyne interferometer. Pdf a novel signal processing method based on phase shift of reference signal is proposed for heterodyne interferometer. An important and widely used application of the heterodyne technique is in the superheterodyne receiver superhet, which was invented by u. A novel signal processing method based on phase shift of reference signal is proposed for heterodyne interferometer. A heterodyne laser interferometric seismometer to measure displacement, a heterodyne laser interferometer. Heterodyne laser vibrometry heterodyne laser vibrometry abramski, krzysztof m.
The light signal is compared with standard or reference light from a local oscillator lo that would have a fixed offset in frequency and. Analog processing based vibration measurement technique. The heterodyne operation facilitates measurement of absolute amplitude and phase of the surface vibration without calibration. Osa laser heterodyne interference signal processing method. Phase measurements in an acdc interferometer prototype. Simple digital phasemeasuring algorithm for lownoise. Optical heterodyne detection of laserinduced gratings. Wataru kokuyama, hideaki nozato, akihiro ohta, and koichiro hattori national metrology institute of japan nmij, national institute of advanced industrial science and technology aist, tsukuba, ibaraki 3058563, japan. This method is called the laser heterodyne vibrometry. Cn201622111u lownoise heterodyne laser interferometer for.
In addition, by applying this method to a commercial heterodyne interferometer. Wataru kokuyama, hideaki nozato, akihiro ohta, and koichiro hattori. The phase of the carrier generated is dependent on the fbg and the environmental perturbations on both fibre arms of the interferometer. When the two signals are mixed, a beat frequency equal to the difference between the two frequencies is created. On the basis of the combination of phase measurement and integer periodic phase measurement, a signal processing scheme, which is used for optical heterodyne interferometer with.
On the basis of the combination of phase measurement and integer periodic phase measurement, a signal processing scheme, which is used for optical heterodyne interferometer with large range, is described. A michelson interferometer based sensor, to monitor the displacement and vibration of a surface, is presented. Therefore the transducer signal will be very dependent of the. By an appropriate processing of the two individual interference patterns a new. Heterodyne laser vibrometry, proceedings of spie 10. We present a 3axis displacement measuring heterodyne interferometer system developed for use with a hene laser at the wavelength of 633 nm having a split frequency of either 3. The complete instrumentation and signal processing are implemented. Signal processing for high precision phase measurements. The bragg cell splits the beam into two, an undiffracted beam and a diffracted beam. Precision displacement measurement by active laser. It requires relatively little sample preparation and it provides noncontact, wideband, absolute, and pointlike measurements.
Pseudoheterodyne signal processing scheme for interrogation. Pdf signal processing method of phase correction for. The utility model discloses a lownoise heterodyne laser interferometer for measuring vibration, which comprises a laser device, a first optical splitter, a first reflector, a second reflector, an acousticoptical modulator, a second optical splitter, a quarterwave plate and a detector. The interferometer is a heterodyne displacement measuring interferometer. Olsonc fowler memorial laboratory, department of otolaryngology, head and neck surgery, college of physicians and surgeons of columbia university, new york, new york 10032. Digital phase demodulation in heterodyne interferometry. Remote laser interferometer with pseudoheterodyne signal.
Design and performance analysis of a novel thermosstructure for measuring. Signal processing the heterodyne interferometer, which is described in this paper, uses two laser beams with a difference frequency of f1. Development of a 3axis displacement measuring heterodyne. Laser heterodyne interferometer with high precision, high speed and long distance has been widely used in displacement, straightness and microangle measurements. The optical layout shown in figure 1 was designed to provide enough degrees of freedom to. A novel signal processing technique using sinusoidal optical frequency. Mechanical vibrations are applied using a pzt piezoelectric transducer. Since the wavelength of the laser diode is temporally multiplexed, only one laser diode lightsource is required, thus eliminating the necessity of aligning two independent optical axes. In a heterodyne interferometer, light is projected against an object of study and motion of the target along the optical axis causes phase and frequency modulations of the backreflected light. The quadrature interferometer explicitly described in ref 2 is a homodyne type.
Errors of laser interferometers using quadrature detectors depend not only on the interferometers themselves, but also on the electronic systems for processing quadrature signals. In order to compensate the time delay due to signal processing, which becomes important at high motion speeds, a predictive position value can be generated at a point in time within the processing interval, which is determined by an external trigger signal. The data shown represent averages over repetitive measurements. Signal error detection and correction of quadrature. Phase measurement of various commercial heterodyne hene. Polarizationbased balanced heterodyne detection method in. Rangeresolved interferometric signal processing using. The laser interferometer space antenna lisa is a joint project of the esa and nasa to. We describe the signal processing for the phase measurement in this paper. Fpgabased smart sensor for online displacement measurements.
In the heterodyne method, shown on figure 3, two laser frequencies are used. Roll angle measurement based on a heterodyne interferometer. A quarterwave plate can be rotated to change the incident linearly polarized laser light into an elliptically polarized light. The signal features of the probe and coupling laser transmitted intensities showed strong differences in. Spectral measurement of the caesium d line with a tunable. Encoding the surface displacement information into the carrier frequency is accomplished in the following manner. Precision displacement measurement by active laser heterodyne. Heterodyne detection not only results in an increase. Introduction optic and fiber optic interference phase scheme are successfully used in creating of hydroacoustic sensors, vibration sensors and measurers of other gntu1,2 the most actual type of the interference sensors is a construction which utilize remote passive all.
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