摘要:

A simple and inexpensive analog technique which corrects spectroscopic signals for pulse‐to‐pulse fluctuations in the output power of an excitation laser is described. The technique is applicable to both linear and nonlinear spectroscopy and, in the latter case, requires no fast electronic function generator. This design yields an improved time‐constant characteristic which parallels the approach of the effective time constant toward RC. Furthermore, since this improvement does not require any preintegration, pulse shape information is preserved. A description of a photoacoustic (PA) spectrometer which incorporates the signal‐correction device and which relies on the photogalvanic effect for wavelength calibration is presented as an example. Finally, signal‐corrected PA spectra of theS1←S0transition in azulene are presented.

ISSN:0034-6748    

DOI:10.1063/1.1137391

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Laser beam wave‐front measurement is important for laser beam quality evaluation and beam control. In this paper we report on a laser beam wave‐front sensor consisting of a phase detector and a scanner. With the use of this sensor, the wave‐front phase profile across a hydrogen fluoride (HF) laser beam has been obtained. The major advantages of this technique are that it is fast, sensitive, and compact. Other features are electric scanning, self‐alignment, noise cancellation, and no drift. Wave‐front sensor operational principles, features, and experimental results are presented. The sensitivity of the sensor was 5°. This sensitivity corresponds to the change of beam quality parameter, the Strehl ratio, by 1%. Hence it is a sensitive beam quality measurement technique.

ISSN:0034-6748    

DOI:10.1063/1.1137392

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Outgassing of contamination in large quantity was observed in a helical TE CO2laser housed in an acrylic (Perspex) chamber. This considerably reduced the sealed operational life of the device. In a helium‐free mixture the laser energy initially improved and then reduced with time, while in the mixtures with helium it reduced monotonically. Water vapor seemed to be the main constituent in the contamination. By circulating the contaminated gas through a trap at dry‐ice temperature, the water vapor was condensed, enhancing the sealed‐off life of the device.

ISSN:0034-6748    

DOI:10.1063/1.1137393

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A simple cost‐effective microprocessor‐based correlator is described which can be used for Gaussian as well as non‐Gaussian light sources. Error calculations are presented to show that there is no significant improvement in accuracy by adopting 4‐bit word length in preference to 3‐bit word length. The instrument can also be used in Raman and Raleigh scattering experiments. A few experimental results are presented bringing out the importance of correlation averaging in S/N enhancement. Some autocorrelograms for fluctuations in the scattered light from polystyrene spheres suspended in water are also presented. The instrument can sample 1500 points and calculate 85 correlations in each scan. All the parameters such as number of samples, number of correlations, number of scans, and the sampling time are user programmable.

ISSN:0034-6748    

DOI:10.1063/1.1137394

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The coercive forceHcof commercially pure iron and an 80% NiFe alloy were measured on toroid samples using a hysteresigraph and on nontoroid samples of the same materials using a vibrating sample magnetometer. Within experimental error, the results were equal for each case. Values ofHcappeared to be insensitive to specimen shape. It appears that the demagnetizing field, which for nontoroid specimens affects the gross shape of the hysteresis loop, can be ignored in the region of low‐field measurements for these materials.

ISSN:0034-6748    

DOI:10.1063/1.1137395

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A simple low‐cost circuit for automatic selection of two successive echoes during measurement of ultrasonic attenuation is described. When ultrasonic attenuation is measured as a function of a varying parameter like temperature, the transit time through the sample also changes, resulting in the shift of echo positions. This calls for manual adjustment of sample pulses used for sample and hold circuits. The present logic eliminates the need for manual adjustment. Details of the logic circuitry along with salient features of peak detectors and sample‐and‐hold circuits used are described. The results of performance tests are presented.

ISSN:0034-6748    

DOI:10.1063/1.1137396

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The electrochemical behavior of 20% strontium‐doped lanthanum chromite (SDLC), deposited onto a 8% yttria‐stabilized zirconia (YSZ) solid electrolyte, has been investigated. The electromotive force developed across the interface SDLC/YSZ and a Pt/YSZ reference at 0.21 atm (air) corresponds to the Nernst theoretical relationship. This behavior has been tested between 700° and 1000 °C in the ranges 100–10−5and 10−13–10−20atm of oxygen, the lower pressures by the equilibrium of carefully calibrated steam and hydrogen mixtures. Although not demonstrated, it is probable that the oxygen pressure range of applicability of this mixed oxide electrode covers the entire field of pure ionic conductivity of any zirconia‐base electrolyte. The fair agreement between the measured values and the theoretical emf values, the resistance of the electrode layer to scaling, as well as its good thermodynamic stability, suggests SDLC as a possible alternative to platinum in high‐temperature oxygen pressure sensors.

ISSN:0034-6748    

DOI:10.1063/1.1137397

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A spectroradiometer has been designed for the study of crop reflectance characteristics in the spectral range of 400–1000 nm. Since the instrument records the ratio of incoming to reflected radiation the values obtained are independent of variations in solar elevation, and azimuth angle and atmospheric conditions. A filter wheel with four interchangeable interference filters is used for wavelength selection. The spectroradiometer traverses above a crop canopy on a movable track. This makes it possible to compare measurements from various locations several times in an hour, and to study more than one canopy a day. This instrument provides agronomists with data to estimate crop canopy characteristics such as leaf area index (LAI) rapidly and nondestructively. It also measures the variability of canopy reflectance introduced by temporal and spatial factors.

ISSN:0034-6748    

DOI:10.1063/1.1137398

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

We present a simple and inexpensive triggering circuit which provides a laser pulse jitter of 0.5 ns.

ISSN:0034-6748    

DOI:10.1063/1.1137399

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A novel optical configuration is described for use with angle‐tuned nonlinear frequency conversion crystals. By double passing the beams through the crystal, the new method suppresses wavelength‐dependent beam displacements more thoroughly and conveniently than previous approaches. This configuration is useful in automatic phase‐matching systems and experiments requiring overlapped beams.

ISSN:0034-6748    

DOI:10.1063/1.1137400

出版商:AIP    

年代:1983

数据来源: AIP