摘要:

A compact, high‐peak‐power, user‐friendly, single‐longitudinal‐mode (SLM) tunable dye laser has been developed. The device yields ≳12 mJ pulses of 6 ns duration and ∼2.7×transform‐limited linewidths of <200 MHz. Seamless single‐mode tunability of ≳20 cm−1is possible without resetting. The dye laser makes efficient use of the pump laser, with ∼10% conversion of the 532 nm pump energy to tunable dye power and occupies <4 m2(including pump laser and all diagnostics). The linewidth of the device can be switched from <200 MHz SLM operation to <0.5 cm−1broadband modeless operation by moving one mirror. This allows rapid interchange between high‐resolution scanning and a ‘‘fast survey scan’’ mode of operation to isolate the spectral region of interest at low resolution.

ISSN:0034-6748    

DOI:10.1063/1.1144612

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A simple and sensitive method for detecting small forces applied to an optically trapped microsphere utilizes the transmitted beam of the trapping laser to monitor microsphere deflections within the potential well of the trap. The rms dynamic displacement detection sensitivity measured in the frequency range from 1 Hz to 10 kHz is ∼1 nm in the radial direction and ∼10 nm along thez(optic) axis. Radiation trapping force constants were calibrated against viscous drag on microspheres in the range between the Rayleigh (r<0.2&lgr;) and Mie (r≫&lgr;) size regimes. For a 1‐&mgr;m‐diam polystyrene sphere trapped with a 60 mW beam the rms spontaneous thermal motion limits the force sensitivity to better than 10−12N and lateral spatial resolution to ∼10 nm in a frequency range from 1 Hz to the viscous rolloff frequency ∼1 kHz. The measured maximum trapping efficiencies are compared with the theoretical predictions of the ray‐optics approximation.

ISSN:0034-6748    

DOI:10.1063/1.1144613

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Autodetachment spectroscopy of a molecular anion has been demonstrated for the first time using a weak infrared diode laser. A low‐power (5 &mgr;W) laser beam overlaps a fast ion beam, driving an infrared vibrational‐rotational transition in a molecular anion. The vibrationally excited anion autodetaches, and the resulting fast neutral is detected. In the first demonstration of the new technique, a previously unmeasured transition in the fundamental (1←0) band of NH−was observed near 2806 cm−1with a signal‐to‐noise ratio of 15:1. There is reasonable agreement between calculated and observed signal strengths. Future instrumental improvements are expected to yield substantial improvement in sensitivity. The present experiment extends the range of applicability of autodetachment spectroscopy beyond the range of color‐center lasers. With straightforward improvements, the technique is applicable to a number of larger molecular anions having low electron affinity.

ISSN:0034-6748    

DOI:10.1063/1.1144614

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A method for the determination of a focused laser beam waist via photoionization and retarding potential analysis is discussed. The focused laser beam was employed to photoionize gas phase clusters generated from a supersonic cluster source. It intersects the cluster beam at right angle in the first stage of the time‐of‐flight (TOF) acceleration lens assembly. With a simple modification on a laser‐based TOF mass spectrometer, retarding fields were applied right in front of the microchannel plate ion detector to map out the kinetic energy distribution of the cluster ions. The size of the laser beam along the molecular beam axis in the ionization region can then be directly related to this energy distribution. In addition, this method manifests a sensitive probe (within 10 &mgr;m) to the laser beam position.

ISSN:0034-6748    

DOI:10.1063/1.1144615

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

An optical spectrometer for the study of low level optical absorption and reflection of spread monolayers at the air‐water interface is described. This spectrometer is suitable for measurements at wavelengths from ∼350 to 800 nm and has a precision of ∼2×10−5in terms of effective optical density. It employs a dual beam design utilizing fiber optic bundles to guide light and a multichannel photodiode array detection system. Instrumental control and data gathering are designed within Labwindows software. Representative spectral absorption data from chlorophylladegradation kinetics are presented by way of illustration. Comparison of chlorophyllareflection and absorption is also given.

ISSN:0034-6748    

DOI:10.1063/1.1144616

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A modular polarization spectrometry system for the measurement of the degree of polarization (linear or circular) of luminescence intensity is described. It is based on polarization modulation with a photoelastic modulator and two lock‐in amplifiers for signal recovery. Interfaced to the spectrometer is a microcomputer configured with CRT monitor, disk drive, and digital printer to provide system control and to permit digital data storage and data manipulations such as multiple scan averaging and averaged background subtraction. The system described is capable of measuring linearly polarized emission, linearly polarized excitation luminescence, and circularly polarized emission spectra. The modular design also allows the spectrometer to be rapidly and easily modified for the measurement of circular dichroism, magnetic circular dichroism, or magnetic circularly polarized emission. The system performance is demonstrated.

ISSN:0034-6748    

DOI:10.1063/1.1144617

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

We have developed a new design for a cryogenically cooled monochromator employing a thin‐crystal strategy which is capable of handling the central‐cone power of the advanced photon source’s undulator A at machine currents up to 300 mA. The key to the proposed design is to machine two opposing narrow channels in a large, indirectly cooled block of Si crystal, leaving a thin, ∼0.6‐mm‐thick strip of Si. The thin section absorbs only a fraction of the incident beam power so that the operating temperatures of the crystal are in the range where Si has both a very high thermal conductivity and a very small or slightly negative thermal expansion coefficient. The fact that the crystal is operated in the negative range of thermal expansion means that the crystal surface illuminated by the x‐ray beam is always under tension and therefore will not buckle.

ISSN:0034-6748    

DOI:10.1063/1.1145222

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A high‐precision, computer‐controlled monochromator of modest cost is described. The folded sine bar is used for the grating drive that provides high linearity even for large scanning angles. With a 200 steps/turn stepper motor and 600 grooves/mm grating, the minimum step size in first order is 0.05 nm, which can be further reduced. Over the 300–750 nm range, a bandpass better than 0.1 nm and a reproducibility of ±0.05 nm can be achieved. The stray light rejection of 8.9×10−7at 5.5 nm from the laser line is remarkable for this single grating instrument. Its performance promises to be an important tool for most forms of laser spectroscopy.

ISSN:0034-6748    

DOI:10.1063/1.1144618

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Extensive laboratory experiments and measurements are required for the operational evaluation and optimization of thermal gradient programmed gas chromatography (TGPGC). To accommodate these numerous laboratory investigations, an instrumentation assembly has been designed and constructed which possesses the needed built‐in experimental flexibility or adaptability. This system has been configured to test a variety of column sheath assembly designs and their associated open tubular separation columns. It is also used for performance testing many other special TGPGC components, including devices needed for the different types of sample introduction. The major application area of TGPGC is the rapid analysis of complex organic mixtures which cover a broad volatility range. Consequently, this system has been designed to permit exploratory investigations over a temperature range of −100 to 500 °C, while using programmed flows of a variety of inert transport gases. With the use of this instrumentation assembly, operational data and performance assessments can systematically provide the information needed to optimize and spatially compact this different analytical chromatographic procedure.

ISSN:0034-6748    

DOI:10.1063/1.1144619

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Development of initial versions of hardware and software for a Hewlett‐Packard HP‐5971A mass selective detector (MSD) was performed in order to improve its capabilities for monitoring gaseous waste streams. The development allowed for initial evaluation of the feasibility of the conversion of the MSD from an integrated gas chromatography/mass spectrometry (GC‐MS) detector to a stand‐alone, on‐line, real‐time mass spectrometry (SOR‐MS) detector. Chemical compound quantitation is accomplished via mass spectrometric step heights, rather than gas chromatographic peak areas or heights. Contributions of more than one chemical compound to a singleM/Zratio are accounted for by nonlinear deconvolution of the mass spectrum, provided a calibration can be obtained for all contributing chemical compounds. The enhanced MSD was tested by a number of calibration and monitoring experiments in order to evaluate the potential and limitations of the conversion. With sufficient care and awareness of the potential and limitations, it appears to be possible to convert the GC‐MS detector to a SOR‐MS detector. In particular, this conversion could allow for simple monitoring of reactive chemical compounds.

ISSN:0034-6748    

DOI:10.1063/1.1144620

出版商:AIP    

年代:1994

数据来源: AIP