Laser interferometer

Wise, J.L. and L.C. Chhabildas (1986), Laser Interferometer Measurements of Refractive Index in Shock-Compressed Materials, in Shock Waves in Condensed Matter (edited by Y.M. Gupta), Plenum, New York, pp. 441-454. 

Barker, L.M., and Hollenbach, R.E. (1972), Laser Interferometer for Measuring High Velocities of Any Reflecting Surface, J. Appl. Phys. 43, 4669-4675. 

Fig. 3.5 Principle of a laser interferometer for absolute calibration of the transducer velocity. Li and L2 denote the lengths of the two light paths of the split laser beam, giving a path difference A5 = 2(Li - L2)...

A sphere has a larger mass than a typical bar (L = 5D) resonating at the same frequency, and because it is equally sensitive for all directions and polarizations it has a cross-section (for the same material) that is about 75 times larger. A single sphere is also capable of determining the source direction and polarization. A spherical detector is the only detector for GWs with isotropic sky coverage and the capability of finding the location of the source. Both laser interferometers and bar detectors are unable to do this with just one detector six bar detectors would be needed to build an omni-directional observatory. 

Quantitative Analysis of a Laser Interferometer Waveform Obtained During Oxygen Reactive-Ion Etching of Thin Polymer Films... 

Table I. Calculation of Polymer Refractive Index from Laser Interferometer Waveform during Oxygen RIE...

The full expression for the reflected intensity of a laser interferometer in a plasma/polymer/silicon system can be used to measure the polymer refractive index to within about 3 percent. 

Dissolution Measurement. Resist solutions 1n mixtures of Isoamyl acetate/cyclohexanone/methyl Isobutyl ketone (90 5 5 by volume) were filtered through 0.45 pm disc filters, then spin-coated onto silicon wafers at about 2000 rpm. The coated wafers were prebaked 1n a convection oven at 90°C for 1 hour, then stored 1n a desiccator. The basicities of the alkaline solutions were titrated by a standard HC1 solution with a Fisher Accument pH meter, Model 805 MP. The film thickness 1s about 2 pm. Resist dissolution was measured by a He-Ne laser Interferometer 1n a thermostated bath at the desired temperatures (12.131-... 

Thermal Expansion Measurement. Thermal expansion measurements were made with a laser interferometer dilatometer (2Q) with a strain resolution of approximately 2x10 6. The temperature cycle for all tests went from room temperature to a maximum of 121°C (except where noted), down to -157°C and back to room temperature. Thermal strain data were taken at approximately 20°C increments with a 30-minute hold at each temperature to allow the specimen and interferometer to reach thermal... 

The laser interferometer consists of two coupled resonators, one containing the laser, the other the plasma under investigation (Fig. 10). The laser radiation, reflected back from mirror A/s, which contains phase information about the refractive index of the plasma, interferes with the laser wave in cavity A, resulting in an amplitude modulation of the laser output 267). This modulation can be related to the refractive index and therefore to the plasma frequency and electron density. With a curved rather than a planar mirror, the sensitivity can be increased by utilizing transverse cavity modes 268). 

Phase changes as small as 2 tr x 10 rad have been detected 269) by using a null method where phase drifts of the apparatus are compensated by a calibrated and controllable dielectric in cavity B. The response time of this laser interferometer is less than 5 psec when operated at 3.39 pm and repetitively pulsed plasmas can therefore be investigated. Gerardo etal. 270) even reached a time resolution of... 

Since the phase shift of light passing through a plasma is proportional to its wavelength, a 337 pm cyanide laser interferometer, described by Kon etal. can be 100 times more sensitive than one operated at 3.39 p. 

A laser interferometer is shown schematically in Fig 1. The parameter measured is the free surface velocity of the specimen material. The principle of operation is as follows. Light from the single frequency gas laser is focused on the... 

Fig 1. Laser Interferometer System (The velocity of the reflecting surface is re ated to the number of fringes observed by the photomultiplier)... 

The major advantages of the laser interferometer over previous free surface systems are the high time resolution and the high surface velocity capability. The limitations in rise time are iimited by the capability of the photomultiplier or oscilloscope recording system. The bandwidth of each system is typically 600 MHz or a response time of 1 nsec (Ref 13)... 

Refractive lenses must always be used in the step-and-repeat mode because the field size they cover is very much smaller than a silicon wafer. Sample position is either tracked by a laser interferometer, after an initial reticle to wafer alignment, or the reticle and sample are aligned with respect to each other at every chip site (12-17). Alignment at every chip avoids errors... 

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