摘要:

We discuss the design and development of Ranicon detectors for optical photon counting imaging on ground‐based telescopes. The significant factors which determine the performance of these detectors are found to be the proximity focusing stage, the microchannel‐plate stack (MCP), and the signal processing electronics. For applications in optical astronomy, the low photon counting efficiency typically found with optical MCP‐based detectors, due to ion barrier films, presents an additional consideration. We review the performance of each stage of the Ranicon detector and the techniques for achieving optimal performance. A new approach to the signal processing electronics reduces nonlinearity, while achieving increased processing speeds and a position error corresponding to <21 &mgr;m FWHM. A significant improvement in detector performance is achieved with an advanced Ranicon incorporating a reduced proximity focusing gap and an unfilmed input plate in the MCP stack. The theoretical spatial resolution of both standard and advanced Ranicon designs is derived and compared to the experimentally determined values. For the advanced Ranicon, this spatial resolution is shown to be typically 40 &mgr;m FWHM at ∼650 nm. The point spread function of the Ranicon system is shown to be stationary over the active imaging area, principally due to the removal of nonlinearities and noise sources from the signal processing electronics.

ISSN:0034-6748    

DOI:10.1063/1.1139709

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

We have placed a scanning tunneling microscope (STM) in the sample stage of a scanning electron microscope (SEM). This allows us to focus the tip on a preselected spot for STM operation with a precision of 0.5 &mgr;m. We are able to check the state of the sample and the tip during STM operation by simultaneous use of the SEM. We are also able to correlate the images given by both techniques.

ISSN:0034-6748    

DOI:10.1063/1.1139710

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A simple four‐terminal conductance bridge circuit, which provides high‐resolution measurements of the current–voltage characteristics,dI/dVandd2I/dV2, as well as capacitance anddC/dVmeasurements, is presented. Current measurements in the wide range 1 nA–10 mA are possible and modulation voltages down to 1 &mgr;V can be used to achieve high resolution. The circuit has been used successfully for tunneling spectroscopy on GaAs–GaAlAs field effect transistor structures.

ISSN:0034-6748    

DOI:10.1063/1.1139711

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The design and performance of a low‐energy ion gun system suitable for surface analysis is described. The ion gun system is capable of delivering up to a 0.72 &mgr;A beam of Ar+ions at a potential of 500 eV into a spot diameter of 1 mm. This performance is accomplished by using ion optics to refocus the space‐charge diverging beam along the 44‐cm path to the target. The ion optics have been optimized by the use of a new simulation program,chden, which can model a series of lenses and the effects of space‐charge forces.

ISSN:0034-6748    

DOI:10.1063/1.1139712

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A velocity selector wheel of novel spiral groove design was constructed and successfully tested. The wheel can be used to select a narrow band (∼±1.2%) of velocities from a molecular beam while presenting an effective open time of 38%. No velocity sidebands are transmitted and alignment is relatively simple. Experimental measurements verified performance essentially as predicted.

ISSN:0034-6748    

DOI:10.1063/1.1139713

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A new picosecond flash photolysis apparatus is described which makes extensive use of fiber optics in the probing beam pathway. The apparatus is simple and easy to use. The absorbance resolution and accuracy are greatly enhanced and allow for quantitative determination of properties of transient species. The capability of the system is illustrated by determining the excited singlet state absorbance properties of erythrosine and rose bengal.

ISSN:0034-6748    

DOI:10.1063/1.1139714

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

The estimation of exponential decay lifetimes is important in many areas of physics, but often difficult if the waveform produced by some particular process (say, fluorescence decay) is noisy. We have used a simulation technique which makes it possible to model accurately two common waveform analysis methods. Results from actual experiments can be compared with those produced by the simulation in order to investigate the nature of the measurement system’s precision limits and thereby effect a reduction of the measurement error. Specifically, an algorithm calculating decay lifetime from two data points exhibited a one‐sigma error of 4% when the measurement signal‐to‐noise ratio was 40:1, compared with a 0.1% error of a least‐squared error algorithm under similar conditions.

ISSN:0034-6748    

DOI:10.1063/1.1139715

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

Resonance Raman studies on transient molecules have raised a problem about characterization of a photolabile species. Therefore, in order to observe the Raman and absorption spectra of the same spatial region of the sample at the same time, we have constructed a novel device and applied it successfully to monitor the transient species involved in an enzymic reaction of horseradish peroxidase and in photodissociation of the carbon monoxide adduct of hemoglobin.

ISSN:0034-6748    

DOI:10.1063/1.1139716

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

A new design for an infrared cell useful for studies of the spectrum of surface species on high area solids is presented. The cell is well suited over a wide temperature range (100–1000 K). Other demonstrated features of the cell include ultrahigh‐vacuum operation, temperature control to ±1 K, linear and rapid temperature programmability and low‐temperature gradients across the powdered sample. The method of sample preparation and support minimizes both heat and mass transport effects. A detailed literature search of previous infrared cell designs is included. Results of the application of the new cell design to the high‐temperature dehydroxylation of Al2O3are given as an example of the performance.

ISSN:0034-6748    

DOI:10.1063/1.1139717

出版商:AIP    

年代:1988

数据来源: AIP

摘要:

In this article, a fluorescence decay‐time thermometer using ruby crystal as the transducer material and carefully designed signal processing, with a light‐emitting diode source and solid‐state optical detection is reported. Results over a range to 170 °C are discussed with a standard deviation in the measurement, at best, corresponding to ±0.04 K, in laboratory tests.

ISSN:0034-6748    

DOI:10.1063/1.1140257

出版商:AIP    

年代:1988

数据来源: AIP