摘要:

A simple and inexpensive method is described for extending the tuning range of a conventional cw CO2laser into the 11–13‐&mgr;m region. The technique consists of optically pumping a mixture of NH3in Ar confined in a capillary waveguide. An output power as high as 1.9 W is attained in the 12‐&mgr;m region from a pump power of only 8.8 W and a total of 12 laser transitions are observed in15NH3. The construction of a compact line‐tunable laser is described.

ISSN:0034-6748    

DOI:10.1063/1.1139423

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

Scaling of a CO laser device of closed‐cycle self‐sustained discharge‐excited type has permitted the attainment of a maximum output power of 3.1 kW. The device incorporates two heat exchangers, operating, respectively, on freon R502 and liquid nitrogen. This permits regulation of the working gas temperature to any given level between room temperature and 120 K.

ISSN:0034-6748    

DOI:10.1063/1.1139424

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

The design and construction of a unique and precision pressure cell suitable for use in light‐scattering experiments has been described. The cell has been adapted to allow scattering experiments from liquid samples. The optics of the cell has been especially designed to obtain a higher signal‐to‐noise ratio. The cell has been designed to be small and compact with sample volume ∼40 mm3. However, it still has a large heat capacity (∼250 J/K) which ensures easy and stable temperature control of the sample. The cell can sustain hydrostatic pressure up to 1000 bar and temperature up to 150 °C. When operated in the constant temperature and pressure mode it offers long‐time (∼16 h) temperature and pressure stability of ±2 mK and ±0.05%, respectively, in this entire range.

ISSN:0034-6748    

DOI:10.1063/1.1139425

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A long path cell has been designed and constructed for absorption measurements at temperatures ranging from 215 to 470 K and at pressures from vacuum to 10 atm. It enables us to measure temperature and pressure dependence of the spectra and reaction rates of gases of atmospheric interest.

ISSN:0034-6748    

DOI:10.1063/1.1139426

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

We report a new type of normalization procedure for modulation spectroscopy experiments in order to obtain the relative change in the reflectance (transmittance) spectrum &Dgr;R/R(&Dgr;T/T). Our new technique utilizes a servomechanism driven variable neutral density filter which keeps the dc component of the signal from the detector constant by varying the intensity of the light striking the sample. This method is particularly useful for photoreflectance measurements which can have background problems due to scattered pump light and/or photoluminescence. Advantages for other modulation spectroscopies, particularly in the region of the fundamental band gap of semiconductors, also will be discussed.

ISSN:0034-6748    

DOI:10.1063/1.1139427

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

Using a computer interfaced original apparatus, we can analyze the fluorescence decay time of a single living cell. This apparatus can measure rate constants in the range of one to few hundred nanoseconds. The smallest sample analyzed was 5×5×5 &mgr;m. We obtained enough sensitivity to measure the fluorescence of about 105molecules of benzo(a)pyrene with a signal/noise ratio equal to 5. The signal was then defined with 300 points and experiment was 60 s long with a laser pulse frequency equal to 100 Hz. Distortions were less than 3% of the signal. Different kinds of information became accessible: statistical comparison on cellular populations and variation with time of studied parameters. As an example of applications, the intrinsic cell fluorescence has been analyzed in order to determine the amounts of bound and free NAD(P)H in single living cells.

ISSN:0034-6748    

DOI:10.1063/1.1139428

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

We have developed an imaging photoelectron spectrometer based on a simple electrostatic immersion lens with the capability of measuring photoemission intensity as a function of the parallel component of electron wave vector throughout the Brillouin zone. The image is a simple rectilinear mapping of thek∥component of the wave vector in reciprocal space. Using a retarding field‐energy selection system, it is possible to energy select and image the various states below the Fermi energy. We obtain an energy resolution of 0.3 eV and ak∥resolution of 0.04 A˚−1. The distribution of photocurrent is amplified onto a phosphor screen by a channel electron multiplier array. The image on the screen is then picked up with a charge‐coupled device (CCD) camera so that the digitized image can be both position and energy analyzed. The performance of the system is demonstrated by imaging the photoelectron distribution from a Cu(001) single crystal. We find that the intensity distribution of emission inkspace reflects the dispersion of the projected bulk energy band structure.

ISSN:0034-6748    

DOI:10.1063/1.1139429

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A photoelectron correlator based on the measurement of the joint probability distribution function in the arrival times of eight stop pulses following a single start pulse is described. This correlator has a measurement interval of 5 &mgr;s and delay time resolution of 2.5 ns. With an eight‐stop capability, much higher count rates can be used without fear of distorting the intensity–intensity time correlation function due to saturation. Thus the accumulation time becomes tolerable for acceptable signal‐to‐noise ratios in time correlation function measurements with such a short delay time increment.

ISSN:0034-6748    

DOI:10.1063/1.1139430

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

First‐ and higher‐order caustics and spectra of the Moellenstedt analyzer are computed. It is found that the higher‐order caustics and spectra are due to multiple deflections of the electrons in the high chromatic aberration region of the Moellenstedt analyzer. These spectra consist of two parts: the caustic spectrum and noncaustic spectra, the so‐called ‘‘ghost’’ spectra. The only reported ‘‘ghost’’ spectrum is reprodued by the calculation. Finally, the effects of changing the geometrical construction and the importance of determining the optimum operating point are discussed.

ISSN:0034-6748    

DOI:10.1063/1.1139431

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

We present some aspects of the realization of a new angular resolved photoemission spectrometer using a magnetic deflector. The photoelectrons are dispersed according to their energy and emission angle and focused onto a detector where the band structure appears in real time. The prototype has been realized around a toroidal magnetic field optimized by computer simulation. We discuss here the energy and the angle resolution of the whole system, related to some compromises in the technical realization as the field limit effects. The main result is that we obtain a complete display of the valence‐band structure (in a plane) with a classical light source in an integration time of 10 s, which is shorter than the time needed by a classical spectrometer by several orders of magnitude.

ISSN:0034-6748    

DOI:10.1063/1.1139432

出版商:AIP    

年代:1987

数据来源: AIP