Conventional discharge lamp

The absorption spectroscopy of transients (flash photolysis) is the most valuable tool for studying the decay of electronically excited species and reactive intermediates 360,379) Xhe limiting factor in the observability of a transient is the duration of the flash 10-8 sec. for conventional discharge lamps and 10-9 sec. for a Laser set-up 536)t... 

Excitation spectra of D API and Hoechst 3 3 342 are too short for most of the lasers and mirrors that are supplied with commercially available laser scanning microscopes, although these dyes can be imaged in conventional fluorescence microscopes with Xenon or Mercury arc discharge lamp or when using HeNe laser/UV system or multiple photon microscopy... 

In this chapter, we review the instrumentation presently available for studying near-IR fluorescence. This includes modern semiconductor devices such as diode lasers and photodiode detectors and also more conventional devices such as discharge lamps and photomultipliers which are traditionally more usually associated with the study of UV/visible fluorescence. Throughout the chapter emphasis will be placed on the novel red/near-IR aspects of instrumentation and we will assume that the reader has a knowledge of the basics of steady-state and time-resolved techniques to the level consistent with Volume 1 of this series. 

While conventional or high-intensity (boosted output)4 hollow cathode lamps are usually simply operated at room temperature, electrodeless discharge lamps are sometimes cooled with a regulated flow of air maintained at a constant temperature,5 and this flow too must be optimized with respect to signal-to-noise ratio. Sometimes these sources are operated in a vacuum jacket to enhance sensitivity and/or to improve stability.6... 

Conventional photoelectron spectroscopy uses a rare-gas discharge lamp to produce radiation at the wavelength of the He 2p <— Is atomic transition (hu = 21.218 eV). Synchrotron radiation is now widely used for PES because its photon energy is widely tunable yet monochromatic. The initial state, in the first PES experiments, has been the molecular ground state but now, by exploiting Resonance Enhanced Multi-Photon Ionization (REMPI) excitar tion/detection schemes (see Section 1.2.2.3), any excited state of the molecule can be used as the initial state for PES (for a review, see Pratt, 1995). 

As radiation sources in AAS, those line sources are mainly used that emit the spectral lines of one or more elements. Line sources make it possible to use conventional instead of high-resolution monochromators, as the monochromator only has to isolate the line of interest from other lines (mainly lamp fill gas lines). Hollow cathode lamps and electrodeless discharge lamps are the main types of lamps employed. 

As the cold-vapor mercury sample is already in the atomic state, there is no need of an atomizer, per se. The vapor, transferred directly from the cell or desorbed as a plug from a heated amalgamation trap, is commonly swept into a moderately heated (resistance wound heating to 200°C) 10 cm quartz T-tube located within the optical beam of a conventional AA spectrometer. Attenuation of an intense electrodeless discharge lamp line source at 253.7nm is used as a measure of the absorption. Alternatively, dedicated continuum source AA-based spectrometers fitted with long path absorption cells (30 cm) are frequently used to increase sensitivity and detection limit. 

Conventional light sources A significant amount of research has been done to develop more intense conventional sources to increase the fluorescence signal size. Conventional light sources that have been used for AES include hollow cathode lamps (HCLs), electrodeless discharge lamps (EDLs), and continuum sources. 

An intense short pulse of UV or visible radiation is used to electronically excite the sample, and the subsequent absorption changes are probed spectrophotomet-rically. The technique was first introduced by Norrish and Porter in 1949 [18] and at this time gas-filled discharge lamps were used, limiting the time resolution, which is principally governed by the duration of the excitation pulse, to microseconds. This is now usually termed conventional flash photolysis. However, with the development of laser pulsed techniques in place of flash excitation, the time resolution has been progressively reduced to subpicosecond, particularly with the use of mode-locked solid state lasers. Much current work utilises nanosecond time resolution with pulsed lasers such as ruby, neodymium and excimer lasers. 

Table 9.1. Comparison between a conventional light source (RF discharge lamp) and a single-mode dye laser...

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