摘要:

A high‐power, frequency‐stabilized laser source is required for an atomic force microscope which uses interferometric techniques to obtain distance measurements with picometer resolution. For this purpose, the oscillation frequency of a 10 mW multimode He‐Ne laser was stabilized using a new technique. Optical interaction between the longitudinal modes synthesizes intermode beats. Frequency of the intermode beat signal changes periodically with respect to cavity thermal expansion. This phenomenon is explained by the concept of ‘‘frequency pulling.’’ The secondary beats synthesized by the interaction between the intermode beat signals also change due to frequency pulling. The relation between the secondary beat of an intermode beat frequency and the laser cavity length is utilized for the stabilization of laser frequency. The change in the frequency of the secondary intermode beat is employed as the feedback signal to control the length of the cavity of the laser. To detect the frequency change in the secondary beat signal, a simple microwave electronics circuit was designed. An excellent frequency stability (instability: ±2 parts in 108) and high‐power laser output were obtained successfully using this simple technique.

ISSN:0034-6748    

DOI:10.1063/1.1144365

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We describe a sensitive polarimeter for measuring optical rotation induced by chiral molecules in solution that operates in the reflectance mode. A polarized light beam is made to pass through a liquid sample two or more times before detection by reflecting the beam from the surface of the sample container. The optical activity of the sample is measured using a differential polarization detector. Our results show that, for certain initial polarization states and angular orientations of the beam with respect to the glass interfaces, high sensitivity to changes in the concentration of the sample can be achieved. Results of a theoretical analysis of the technique were confirmed by experiments in which optical rotation of glucose in water was measured using a simple apparatus that employs a light‐emitting diode source. Glucose sensinginvivoand on‐line monitoring of industrial processes using integrated optoelectronic sensors are discussed as potential applications.

ISSN:0034-6748    

DOI:10.1063/1.1144366

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A selected ion flow tube apparatus is coupled with laser induced fluorescence (LIF) detection for the selective monitoring of ion vibrational states and their reactions. Mass selected ions are injected into a flow tube with a venturi inlet using He carrier gas. A 200 Hz dye laser system provides sensitive LIF detection of the injected ions at densities as low as 1×105cm−3for N+2. The rotational temperatures of the N+2ions are estimated to be ≊300 K using the LIF detection, while the vibrational temperatures can be high and may be varied by the injection potentials. Vibrationally state‐selected ion‐molecule reactions of N+2(v=0, 1, and 2) are studied with N2, Ar, and O2at thermal kinetic energies (Elab<0.1 eV), where translation‐to‐vibration energy transfer is negligible. Isotopically specific charge‐transfer reactions of15N+2(v) with14N2are also studied. The ability to mass select ions and characterize their vibrational states and those of their reaction products allows novel studies of state‐to‐state ion chemistry.

ISSN:0034-6748    

DOI:10.1063/1.1144367

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A Raman system is described which is suitable for rapid determination of Raman spectra of silicates and other weak Raman scatterers under simultaneous high‐pressure and high‐ temperature conditions. Samples are pressurized with an argon pressure medium and Sm:YAG pressure standard in an Inconel 718 or rhenium Merrill–Bassett diamond–anvil cell that is externally heated in a vacuum oven equipped with quartz windows on either side. Raman spectra are excited and collected through the front window using ≊160° scattering geometry. A triple spectrometer in conjunction with a holographic notch filter, disperses the Raman scattered radiation onto a liquid‐nitrogen‐cooled CCD detector. Simultaneously measured Sm:YAG fluorescence spectra are collected through the rear window and routed via an optical fiber to a second multichannel spectrometer system equipped with a diode‐array detector. The high sensitivity of the detectors and the simultaneous measurement technique enable detection of and compensation of pressure drifts occurring at high temperature. The performance of the system is demonstrated by measurement of the positions and linewidths of the high‐frequency Raman modes of polycrystalline forsterite (&agr;‐Mg2SiO4) at temperatures up to 930 K at pressures of ∼8 GPa and up to 842 K at pressures in the range 12–14 GPa.

ISSN:0034-6748    

DOI:10.1063/1.1144368

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Time‐resolved UV‐visible absorbance measurements made after laser photolysis are important for mechanistic understanding of many biological systems. Some of these systems are available in extremely small quantities and/or are destroyed by light so that averaging strategies for signal‐to‐noise improvement are severely restricted. An apparatus is described which measures the absorbance difference spectrum at a variable delay (10 ns resolution) after photolysis of a 1 &mgr;l sample (optical path 2 mm). After each photolysis pulse the sample is replaced using a pump which delivers 0.5 &mgr;l increments. Waste of sample is avoided by making sure that the sample’s cross section exactly matches the image of the spectrograph slit in the sample cell. Data are presented for photolysis of the bovine visual pigment rhodopsin both in transparent octyglucoside detergent suspensions and more turbid, sonicated disk membrane preparations. Rate constants obtained from a biexponential fit of difference spectra at five delay times from 40 to 640 ns agree well with those obtained previously from much larger detergent samples. Equally high quality results are obtained for the turbid membrane suspensions at longer delay times.

ISSN:0034-6748    

DOI:10.1063/1.1144369

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

For a quasimonochromatic light source with a known spectrum, the polarization Michelson interferometer (POLMINT) can be used as a global polarization state generator that produces totally or partially polarized light at its output in states of known degree of polarization that correspond to points on and within the Poincare´ sphere. Conversely, the spectral and coherence properties of a quasimonochromatic source can be determined from the Stokes parameters of light at the output of the POLMINT measured by a complete polarization state detector as functions of a mirror displacement. Applications of the POLMINT as an ellipsometer are also discussed.

ISSN:0034-6748    

DOI:10.1063/1.1144370

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We describe a new experimental setup for photoluminescence spectroscopy on van der Waals clusters. It consists of a molecular beam apparatus with a cluster beam installed behind a high intensity vacuum ultraviolet synchrotron radiation beamline. Special emphasis was given to the design of a very intense cluster source which can also be used for the preparation of quantum clusters (He,H2). For the determination of the cluster size a time‐of‐flight mass spectrometer can be attached to the setup. In addition, an atomic cross jet is installed in the experimental chamber which can be used for mass separation or for doping of the clusters. The luminescence light can be recorded with several different detectors or spectrally analyzed with a secondary monochromator which is equipped with a position sensitive detector. The pulsed nature of synchrotron radiation provides the basis for time‐resolved measurements in the regime 100 ps–3 &mgr;s.

ISSN:0034-6748    

DOI:10.1063/1.1144371

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A computer‐controlled pulsed electron spin resonance spectrometer operating atS‐band (2–4 GHz) is described. The instrument is designed for the study of weak interactions between paramagnetic centers and surrounding magnetic nuclei by electron spin‐echo modulation techniques. The incorporation of loop‐gap resonators gives good sensitivity and allows use over the full octave bandwidth range. Free‐induction decay and electron spin‐echo signals at room temperature and at liquid‐helium temperature are shown in selected sample types. The expected increase of the electron spin‐echo modulation depths relative toXband (∼9 GHz) frequencies is demonstrated for proton modulation.

ISSN:0034-6748    

DOI:10.1063/1.1144372

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We have embodied a new version of two‐dimensional display‐type spherical mirror analyzer [H. Daimon and S. Ino, Rev. Sci. Instrum.61, 57(1990)]. A couple of concentric hemispherical small grids and 12 pairs of obstacle rings have been attached to the original type of analyzer in order to operate with a constant pass‐energy mode and improve the uniformity of the energy resolution of the analyzer all over the detection area, respectively. We performed a test on the resolution of the analyzer, and applied it to the simultaneous angle‐resolved photoelectron spectroscopy on the band structures of single‐crystal graphite (Kish graphite) within the acceptance cone of ±50°. The observed band structure is in good agreement with those reported by other investigators. We observed a ring‐like pattern which enlarged as the binding energy approached the Fermi level. This ring is ascribed to the cross section of the &pgr; band. Although the designed energy resolution is 1% of the pass energy, the minimum value realized reached in this study was 0.2 eV for the pass energy of 10 eV [H. Daimon, Rev. Sci. Instrum.59, 545 (1988);61, 205 (1990)].

ISSN:0034-6748    

DOI:10.1063/1.1144373

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A low‐energy diffuse scattering electron spin detector for spin‐resolved x‐ray photoelectron spectroscopy (SRXPS) is described. The detector is coupled to a commercial 152‐mm mean radius, 150° spherical sector electrostatic electron energy analyzer. Electron optics are described for both the transport of photoelectrons from the energy analyzer exit slit to the gold scattering target, and from the gold target to the spin analyzer electron detectors. The spin detector has an effective Sherman function of 0.078±0.008, with a figure of merit of approximately 4×10−5. The electron optical phase space acceptanceEA&OHgr; of the detector is 623 eV mm2 sr. The SRXPS apparatus performance is demonstrated with SRXPS spectra from ferromagnetic Fe and a cobalt‐based ferromagnetic glass.

ISSN:0034-6748    

DOI:10.1063/1.1144374

出版商:AIP    

年代:1993

数据来源: AIP