摘要:

This review describes recent instrumentation developments of the thermal lens techniques. It will begin with a brief discussion of the theory of the techniques. Its main focus is, however, on the detail description of various instruments. Specifically, the discussion will begin with the description of single beam instruments which were initially developed following by dual beam instruments. Elaboration will be focused on some of the most sophisticated instruments which were developed recently. These include differential thermal lens instruments, multiwavelength and spectral tunable instruments, circular dichroism spectropolarimeters, rotoreflecting instruments, and miniaturized thermal lens instruments. Selection of lasers, focusing, modulation, sample position, sample cells, data acquisition, noise reduction, and applications of acousto‐optic tunable filters will also be discussed. The future of the techniques in terms of instrumentation will be finally forecasted. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147512

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A new photothermal technique is proposed. It is based on the temperature characteristic of the dielectric constant of light‐irradiated material. When chopped light is absorbed in a dielectric material, an alternating variation of capacitance is caused by the heat produced due to light absorption and is detected by using a frequency demodulation technique. A quantitative derivation is presented for the alternating capacitance variation in terms of the optical, thermal, dielectric, and geometric parameters of the system. The experimental results for lead zirconate titanate ceramics, barium titanate single‐crystal, TiO2–Bi2Ti4O11ceramics, and ethyl alcohol are shown, where the observed signals agree with theoretical ones very well. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146544

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We show how to measure dynamic specific heat and thermal conductivity of a solid or liquid sample using the 3&ohgr; technique, which is an ac‐modulation method where we use a heater simultaneously as the sensor. By varying the width of the heater relative to the thermal decay length, one can choose the proper regime to measure thermal conductivity or specific heat. The technique is applied to window glass and the results confirm the validity of the method. Experimental results for potassium dihydrogen phosphate crystal demonstrate the first‐order transition at the Curie point, and the dynamic specific heat of supercooled liquid potassium–calcium nitrate is shown. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146545

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Mode‐locking techniques are well known for the generation of short pulses. However, little work has been done to evaluate the use of this technique with long wavelength (10.6 &mgr;m) CO2waveguide lasers. For this region of the spectrum, mode locking has the advantage of requiring smaller modulation voltage than other conventional modulation techniques which makes possible the generation of pulses at a frequency higher than 100 MHz. The efficient generation of pulses at these frequencies makes this type of laser attractive for active imaging at long wavelengths. In this paper, the design of a mode‐locked waveguide CO2laser is reported and its characteristics of operation are compared with an existing model. Significant depth of modulation is observed at 190 MHz with an applied modulation voltage lower than 50 V. From the comparison between the experimental results and the theoretical model, improvements are proposed. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146546

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A phase fluorometer based on a low‐cost and versatile high‐frequency modulated light source and a fast gain‐modulated photomultiplier is described. The apparatus is particularly well‐suited to high‐sensitivity frequency‐domain fluorescence measurements requiring ultraviolet excitation. The system is very compact since it features a directly modulated light source, a miniature photomultiplier tube, and an rf synthesizer on a PC board. Equipped with a suitable fiber optic probe sensor, the device has potential as a portable unit for a wide range of remote sensing applications. The lamp can be modulated at frequencies up to 120 MHz and the phase fluorometer has been tested at up to 70 MHz with a range of fluorescent lifetime standards containing quinine sulfate quenched with sodium chloride. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147228

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A new method of high speed simultaneous deconvolution of multiple fluorescence decays with equal lifetimes and variable amplitudes is offered. The absence of need for initial guesses and comparably high accuracy make it suitable for obtaining initial conditions for other methods like iterative least squares. We discuss optimizations of the deconvolution procedure based on reductions of the matrix dimension. This establishes a higher processing speed and requires less computer memory. The properties and potential of this method were investigated through tests on simulated decay surfaces. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147226

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

This paper reports an experimental characterization of the EG&G SPCM‐AQ single‐photon avalanche diode module with an active quenching bias circuit that gives a dead time of ∼35 ns for use in high count rate, fast timing applications. A quantum efficiency of ≳70% and an optimal timing jitter with a full width at one‐thousandth maximum of 1.5 ns is obtained if the light is tightly focused to a spot of <25 &mgr;m in the center of the active region, if the signal from the diode before the active quenching circuitry is used as input to the timing electronics, and if an external dead time of ∼55 ns is imposed. Under these conditions, the total probability of obtaining an afterpulse is found to be ∼2×10−3. Limitations of existing time‐correlated single‐photon counting instrumentation for count rates exceeding 106s−1are discussed. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146551

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have compared the circularly polarized x‐ray flux obtained from an elliptical multipole wiggler to that obtained from a planar undulator combined with phase retarding crystal optics. This comparison is carried out for low (3.5–13 keV) and high (50–100 keV) x‐ray energies. For both these energy regimes, we demonstrate that phase retarding crystal optics are not only a viable alternative to specialized insertion devices but in some cases provide a superior source of circularly polarized x rays. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146552

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Modulation of an ion beam is crucial to several applications in time‐of‐flight (TOF) mass spectrometry, especially for tandem TOF instruments which require selection of a particular precursorm/z(mass to charge) value prior to fragmentation. Here we present a detailed description of an ‘‘interleaved comb’’ ion deflection gate device with suitable electronics which offers a performance advantage over the more commonly used deflection plate devices. We demonstrate unit mass resolution for selection tom/z167 in the tandem TOF instrument constructed in our laboratory. Calculations suggest that the real time of unit resolution for our experimental arrangement is greater than 300. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146553

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

This paper presents a method for estimating the resonance frequency of a bridged loop‐gap resonator (BLGR). It first describes the structure of the BLGR and its equivalent electrical circuit, and then a procedure for calculating the resonance frequency is revealed. In this procedure, node analysis, which is a circuit theory, is applied to calculate the branch voltages of the equivalent circuit. Finally, this paper reports on the calculations and measurements of the resonance frequency, and the validity of the method for estimating resonance frequency. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1146554

出版商:AIP    

年代:1996

数据来源: AIP