摘要:

We report a method to stabilize the frequency of a laser diode for a long time by means of four feedback loops including a digital feedback circuit. The laser frequency was locked at a saturated absorption peak of cesium atoms. In addition, by feeding back the frequency error signal to the temperature controller of the laser diode, the power as well as the frequency was stabilized at the same time. The power stability of 0.03% was obtained, which was 260 times better than that obtained without the feedback. The frequency stabilization continued for over 1 week and the fluctuation width was about ±0.5 MHz around the locking point. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147091

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We demonstrate the design and implementation of a fiber‐optic‐bundle beam delivery system for particle image velocimetry (PIV) applications. The system is designed for the transmission of high peak power pulses (≳20 mJ) from aQ‐switched and frequency doubled Nd:YAG laser. A fiber bundle offers advantages over a single fiber in beam delivery systems for light sheet formation. The damage‐limit‐maximum power that can be transmitted is greater for the bundle than for any of its component fibers, and the quality of the derived light sheet is higher than that obtainable from a single large core fiber of power handling capacity equivalent to that of the bundle. The beam delivery system was demonstrated in PIV measurements on a premixed propane‐air flame. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147093

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We report measurements on a 1.75 m long Fabry–Perot cavity locked to a Nd:YAG tunable laser using the Pound–Drever technique. The cavity decay time was measured to be about 291 &mgr;s corresponding to a quality factorQof about 5×1011, the highest value ever reported for an optical resonant cavity. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147094

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

An interferometer previously developed for measuring instantaneous film thickness of the order of 10 &mgr;m–1 mm [T. Ohyama, K. Endoh, A. Mikami, and Y. H. Mori, Rev. Sci. Instrum.59, 2018 (1988)] has been improved with respect to both facility of handling and accuracy of thickness determination. The improved version of the interferometer uses an expanded laser beam focused aslant on the subject film. The rays reflected from the front and rear surfaces of the film form interference fringes on a screen, which are then recorded in the form of a single snapshot interferogram or as a set of serial interferograms to be geometrically analyzed. Experiments with thin glass plates as sample films verified the expected advantages of the new version over the original one. The improved version of the interferometer was also tested on a liquid film asymptotically thinning as it drained down a vertical plate. The test indicated that the accuracy and precision of the new improved version far exceed those of other transient film‐thickness measuring techniques. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147095

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Pulsed photoacoustic spectroscopy (PAS) technique for immediate measuring absolute optical absorption coefficient is presented. It is based on determination of amplitude‐time characteristics of photoacoustic (PA) signal generated in air surrounding the sample under investigation. The PA signal is excited by a short laser pulse. The sample is placed in the lateral chamber of a three‐chamber PA cell. The difference of PA signals excited in two other chambers is recorded. Time dependence of PA signal for each PA cell chamber is derived. The theoretical predictions are experimentally verified. The pulsed PAS technique presented was tested experimentally by measuring water absorption coefficient at an infrared wavelength. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147096

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

When using a multimode fiber lead in an optical current measurement system, the optical power in the guided modes is often determined by the coupling conditions at the input end of the fiber. If only the skew rays are excited in the fiber lead—under appropriate coupling conditions—the vibration‐induced noise normally experienced in the fiber lead in such an optical current measurement system can be effectively suppressed, especially when a low coherence source and a long length of multimode fiber is used. The experimental conditions for this are considered and discussed in this article. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147097

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The aim of this work is to present an analytical model able to interpret the role of the thin collecting resistive layer on the static performances exhibited by 1D amorphous silicon hydrogenatedp‐i‐nthin film position sensitive detectors. The data obtained show that the devices present a linearity and a spatial resolution, of respectively, better than 99% and 20 &mgr;m for a spatial detection limit of about 80 mm, highly dependent on the characteristics exhibited by the collecting resistive layer that should have sheet resistivities in the range of 10 to 103&OHgr;/sq, as predicted by the model proposed. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147098

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We present a pulsed multiplex absorption spectrometer in which the sensitivity of the cavity ring down absorption detection technique is combined with the multiplex advantage of a Fourier Transform spectrometer. A description of the Fourier transform cavity ring down (CRD) spectrometer—substantiated with first experimental results on the atmospheric band of molecular oxygen—is given. It is shown that as in the case ofnormalCRD spectroscopy, the measurement is independent of light intensity fluctuations provided the spectral intensity distribution of the light source is known and is constant during the measurement. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147092

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We report on a new design for a Fourier transform microwave spectrometer in the spectral region 1–4 GHz, specially constructed for the investigation of rotational spectra of heavy van der Waals complexes. In contrast to the commonly known molecular beam spectrometers using a Fabry–Perot resonator working with TEM00qmodes, the proposed design employs a different type of resonator operating with TE01qmodes. This resonator allows for compact dimensions even at cut‐off wavelengths above 0.1 m. Details of the design, performance data, and example spectra of stable molecules and complexes are given. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147099

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We present an improved method for making pump‐and‐probe optical measurements in the picosecond to nanosecond time range. In this type of measurement, a pump light pulse is used to excite the sample and the resulting changes in the optical properties are investigated by means of a probe pulse that is time‐delayed relative to the pump pulse. In most measurements of this type, a mechanical stage is used to introduce the variable time delay of the probe pulse. As a result of imperfections in the stage motion, alignment problems, and divergence of the probe beam, it has been difficult to make accurate measurements when the time delay of the probe relative to the pump is in the range above a few hundred picoseconds. To overcome these difficulties, we have developed an apparatus that utilizes a single‐mode optical fiber. In order to demonstrate the performance of this system, we present results of experiments in which the flow of heat from a thin film into a substrate has been measured. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147100

出版商:AIP    

年代:1996

数据来源: AIP