摘要:

The characteristics of various cw mode‐locked dye lasers were thoroughly explored, and the characteristics of a pump/probe apparatus employing two such lasers pumped by a single mode‐locked pump laser. First, it was observed that the rf source used to drive the acousto‐optic mode‐locking element in the pump laser, while not affecting the average power or obtainable pulse width, had a profound effect on the noise characteristics of the pump laser, which are in turn passed along to the dye lasers. For a driver based on a tunable frequency synthesizer, pulse jitter on the order of 300 ps was observed, which represents ≊2.5% of the total interpulse time interval. This was deemed unacceptably high, and use of this mode‐locker driver was discontinued. For a driver with a fixed frequency reference source (an oscillating quartz crystal), pulse jitter on the order of 5 ps was measured, a great improvement over the other driver. Next we studied various dye laser configurations pumped by this pump laser. We found that for time resolution of several picoseconds, a pair of synchronously pumped dye lasers employing birefringent filter tuning elements was an excellent source of independently tunable pulse trains, and that these pulse trains were well synchronized with each other despite the absolute timing jitter in the pump pulse train. To obtain better temporal resolution with independently tunable lasers was more problematic, however. A hybridly mode‐locked laser (employing a saturable absorber within a synchronously pumped dye laser) can produce shorter pulses (≤100 fs has been reported), but the lack of temporal synchronization between two of these lasers limits the resolution of a two wavelength experiment to several picoseconds. An attempt was made to reduce this relative timing jitter by crossing two independently tunable hybrid lasers through a common intracavity saturable absorber, thereby temporally locking the pulse trains together. This mechanism failed to work well on time scales longer than a millisecond.  

ISSN:0034-6748    

DOI:10.1063/1.1142586

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A software‐based method for real‐time, active stabilization of tunable diode laser spectral scans is described. The procedure is suitable for use with field and laboratory instrumentation where automated, unattended spectrometer operation is required. An autocorrelation of two high‐resolution reference gas infrared spectra is computed at regular intervals, and the location of the maximum value of the autocorrelation provides the relative abscissa shift between the spectra. Small adjustments to the laser scan parameters are thereby made to ensure that drifts in the laser output frequency are tracked and compensated. Calculations required for stabilization of a 512‐point spectrum can be completed in under 25 ms using an inexpensive, moderate‐speed, array processor installed in a PC.

ISSN:0034-6748    

DOI:10.1063/1.1142587

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A pulsed dye laser system fully controlled by a microcomputer has been developed as a tunable light source for analytical spectroscopy. The system has 13 dyes with a rapid replacement mechanism and a frequency doubler inside, and any desired wavelength from 220 to 740 nm can be instantaneously generated by the aid of the microcomputer control. The absolute wavelength can be automatically calibrated with a newly developed optogalvanic wavemeter with an accuracy of ±1 cm−1over the whole spectral range.

ISSN:0034-6748    

DOI:10.1063/1.1142588

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The development and implementation of the paratellurite (TeO2) acousto‐optic tunable filter as the novel dispersive device are described. It will be demonstrated that this all solid state, rugged filter which contains no moving parts can be used to rapidly diffract white incident light into a selected color beam whose amplitude is kept constant in either pulsed or continuous mode.

ISSN:0034-6748    

DOI:10.1063/1.1142589

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A high‐resolution Fabry–Perot interferometer was inserted in a feedback loop which, by monitoring elements of the fringe pattern, keeps the position of the transmitting window fixed with respect to a given line, taking into account the instability of the radiation source which would produce a wander of the line itself and the noise affecting the tuning of the receiving interferometer. The system, in this preliminary form, is able to lock itself and maintain its position indefinitely for slow and moderately fast varying disturbances.

ISSN:0034-6748    

DOI:10.1063/1.1142590

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Velocity interferometer system for any reflector (VISARs) are used to measure the velocity of targets by monitoring the Doppler shift of laser light backscattered from them. In the design of these systems, there is a trade‐off between signal‐collecting efficiency and depth of focus. We present a VISAR architecture that maximizes the efficiency for any specified depth of focus for velocity sensitivities ranging from 20 m per second per fringe to several kilometers per second per fringe. We consider the usual system where the light going to and from the target is relayed with lenses. We also study fiber optically coupled systems. Our analysis shows that well‐designed fiber‐coupled systems can be as efficient as the equivalent lens‐coupled systems, assuming that the divergence of the fiber‐coupled laser beam is small.  

ISSN:0034-6748    

DOI:10.1063/1.1142591

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We discuss the techniques and describe the circuitry to build a visible diode laser picosecond light source. The rf circuitry is easy and inexpensive to build, and the final package is quite compact. Stable, low jitter, 108‐Hz trains of ∼100‐ps, 670‐nm optical pulses are therefore readily attainable.

ISSN:0034-6748    

DOI:10.1063/1.1142592

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A time‐resolved light‐scattering photometer based on a combination of a fiber optic device (an optical transformer) with an intensified photodiode array detector is described. The key feature includes a baffle arrangement which defines the angular apertures of the scattering angles as viewed by the array detector and limits the background stray light as viewed by the fiber bundles. The instrument, which is a modified version of a previous report [Moseretal., J. Phys. Chem.92, 6723 (1988)], can be used for time‐resolved measurements of angular distribution of scattered intensity from weak to very strong scattering systems.

ISSN:0034-6748    

DOI:10.1063/1.1143817

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Spectroscopic ellipsometry using photoelastic modulator [phase modulated spectroscopic ellipsometry (PMSE)] has been improved in the spectral range. Spectroscopic ellipsometry using the rotating analyzer [rotating analyzer spectroscopic ellipsometry (RASE)] has demonstrated its capability of measuring the reflectivity ratio, &rgr;(&ohgr;), from 1.5 to 6 eV with a single scan, but PMSE has not been able to do so. We demonstrate that PMSE also can measure &rgr;(&ohgr;) from 1.5 to 6 eV with a single scan. We discuss the problems and show their solutions to achieve this goal. We also discuss the accuracy of our PMSE by comparing the spectral data by RASE with those by our PMSE. We find that the simplest possible procedure with our system provides reasonably accurate values, after including the zone average which is easy to perform with our system. The extension of the spectral range is a decisive advantage, especially in studying theE1structure of the wide band gap materials such as ZnSe.

ISSN:0034-6748    

DOI:10.1063/1.1142593

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A cryogenic refractometer is described. It enables preparation of liquefied samples and measurement of their refractive index at low temperatures (down to 20 K). The liquid sample can be a pure liquefied gas or a mixture. The composition of the liquid mixture can be estimated from the volume and pressure of each gas measured during the liquefying process. The determination of absolute values of the refractive index necessitates a calibration, therefore the accuracy is limited to 10−3index unit. Sensitivity and reproductibility are better (5× 10−4) and could be improved to 10−4. The refractive index of pure liquid methane was determined at several temperatures (91–106 K) and 670 nm. The results obtained agree with the published data. The refractive index of mixtures of liquid methane and ethane, with and without dissolved nitrogen, was also determined at 94 K and 1.5 bar total pressure, for which conditions no data were previously available.

ISSN:0034-6748    

DOI:10.1063/1.1142594

出版商:AIP    

年代:1992

数据来源: AIP