摘要:

A two‐dimensional cross‐correlation technique is described, which allows time‐resolved pump‐and‐probe experiments to be performed with two continuous broadband excitations. The progress of a rate process stimulated by one excitation is investigated by the second. Within the linear response limit the technique is characterized by low excitation power and high response energy. Potential applications are in the study of dynamic mechanical and electrical material properties by spectroscopic methods such as nuclear‐magnetic resonance or Fourier transform infrared spectroscopy, and in opticalT1measurements with a time resolution on the order of the inverse bandwidths of the excitations. A two‐dimensional digital interferometer capable of microsecond resolution is described and used to illustrate the principle of the method with an investigation of a two‐input electronic circuit.

ISSN:0034-6748    

DOI:10.1063/1.1139575

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

An active wavelength stabilization and scanning system is described which reduces the dye laser wavelength fluctuation under feedback by detecting the changes in the fringe diameter of a temperature‐stabilized Fabry–Perot interferometer with the help of two photodiodes. An estimate of the wavelength drift due to thermal effects is made. Short‐ and long‐term fluctuations in the wavelength, monitored by recording iodine fluorescence are reported. The system response to a sudden external disturbance to the wavelength was studied.

ISSN:0034-6748    

DOI:10.1063/1.1139576

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A high‐resolution infrared optical absorption spectroscopy system based on lead‐salt tunable diode lasers as light sources has been developed for detection and monitoring of trace gases by resolving their narrow‐width absorption bands. The system is a double beam setup, where a reference cell containing the monitored gas is used for tuning and locking the laser light frequency to that of a desired absorption line and a measurement cell where the examined gas flows continuously at a reduced pressure. Frequency modulation of the laser light is achieved by square waveform modulation of its current source and both the frequency locking and signal analysis devices are based on sample‐and‐hold techniques. The system capability is demonstrated by the monitoring of ammonia traces in human breath. Gas trace monitoring in respiration may prove to be an effective medical diagnostic method.

ISSN:0034-6748    

DOI:10.1063/1.1139577

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

We investigate the factorial moments and photon correlation properties of two Sharp Corporation 780‐nm laser diodes and assess their suitability for use in photon counting and correlation experiments.

ISSN:0034-6748    

DOI:10.1063/1.1139578

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A new design concept of a streak tube is conceived to obtain femtosecond temporal resolution. It is based on four factors as follows. First, in order to decrease the photoelectron transit time spread, one must investigate how high electric field is practically usable near the photocathode. It is found that the value can be increased up to ∼6 kV/mm and this is used as a design value. Second, as the other method to decrease the photoelectron transit time spread, an electromagnetic focusing method must be adopted because there is no region similar to the focusing section of an electrostatic focusing type where the electric potential is low. Third, the focusing magnetic field should be located in a limited region to obtain a very high sweep speed of ∼2×108m/s. And fourth, in the operation, a special readjustment of the focusing magnetic field should be performed to compensate the photoelectron beam defocusing caused by the very rapid transient deflection field. Based on the above, a new streak tube has been designed, manufactured, and tested. The limiting temporal resolution of ∼400 fs has been predicted theoretically and the value less than ∼500 fs has been experimentally produced.

ISSN:0034-6748    

DOI:10.1063/1.1139665

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

Traditionally optical multichannel analyzers (OMAs) have been turnkey instruments. Controllers are now available which replace the OMA console with the users existing computer. The increased flexibility of this approach comes at the expense of increased involvement in the details of system operation. This is particularly the case for pulsed experiments where the detector is gated on for short periods. We report here implementation of an OMA controller hosted by an IBM personal computer using IEEE‐488 communication. A microchannel‐plate intensified detector is used in gated mode to collect spectra of intermediates formed by nanosecond laser photolysis. Three different pulsers for intensifier gating are compared. Both conventional absorbance measurements on transparent samples and diffuse reflectance measurements on opaque low‐temperature matrices are described. In both cases, however, the samples are sufficiently photostable that noise can be reduced by signal averaging using repeated photolysis of the same sample volume. A second paper describes the additional complexity required for high signal‐to‐noise measurements on small quantities of photolabile samples.

ISSN:0034-6748    

DOI:10.1063/1.1139579

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

An optical multichannel analyzer system for obtaining high‐quality spectra of intermediates formed by nanosecond laser photolysis is described. The system is useful for samples which undergo irreversible photochemistry and which are available in limited amounts. Sample volumes as small as 25 &mgr;l are possible and a syringe pump driven by a linear stepper motor is used to deliver fresh sample after each photolysis pulse. The microchannel‐plate intensified detector used here in gated mode can collect an entire spectrum in 5 ns, but proper synchronization of the detector scans is required to avoid severe distortion which can appear as random noise in signal averaging. Noise from various sources such as phosphor lag in the detector, time jitter, source intensity fluctuations, and the photon character of light are discussed. Experimental design for noise reduction is described including diagnostic procedures and light source filtering to produce more uniform signal‐to‐noise ratio throughout the spectrum. Finally, a comparison is made between the noise observed to occur between detector channels and the noise predicted to occur based on the photoelectron gain of the intensifier. The disagreement between these is discussed in terms of the spatial resolution of the detector.

ISSN:0034-6748    

DOI:10.1063/1.1139580

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

An experimental setup for the measurements of multiphoton optical rotary dispersion is described. It is demonstrated that the effect is measurable and amenable to experimental observation. The experiments were carried out on 10% aqueous solutions of (+)−, (−)−, and racemic camphorsulfonic acid.

ISSN:0034-6748    

DOI:10.1063/1.1139581

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

Accurate calculations of the axial chromatic aberration coefficients of symmetric two‐cylinder bipotential electrostatic lenses for three different gap values (0.10D, 0.50D, and 1.0D) are presented. This is an extension of the first‐order properties and the third‐order spherical aberration coefficients published by Harting and Read.

ISSN:0034-6748    

DOI:10.1063/1.1139582

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

The equipotential lines and the trajectories of electrons in a Moellenstedt analyzer are computed. The effects of relativity and the self‐magnetic field of the moving electrons are taken into account. The dispersion, resolution, and caustic position are defined and calculated. The sensitivity of the dispersion and resolution to not only the voltageVapplied to the electrode rods, the electron energyE, the incident angle &fgr;, or the geometrical construction of the analyzer, but also the distanceLbetween the analyzer and detector has been investigated. The caustic position varies strongly with the incident angle and the geometrical construction of the analyzer. The dependencies of resolution on the incident angle and the geometrical construction are significantly reduced in the vicinity of the caustic with the angular spread of the incident electrons remaining the major contributor to the finite resolution.

ISSN:0034-6748    

DOI:10.1063/1.1139583

出版商:AIP    

年代:1987

数据来源: AIP