Sapphire lamps

Figure 2. High resolution spectra of the Na D-line reversal from sapphire lamps operated at higher than normal Na pressures and lower than normal power loadings.

The optical properties of the wall also contribute to the emitted spectra. The usual arc tube wall material, polycrystalline alumina (PCA), has rather low "in-line" transmission and scatters most of the incident radiation. That portion which is scattered back into the discharge medium and that is also in the spectral region inside or near the peaks of the self-reversed resonance lines, is likely to be absorbed. Thus we have found greater Na reversal for PCA arc tube lamps than for sapphire lamps with the same diameters, Na-Hg alloy composition and reservoir temperatures. Indeed, various authors have reported 3-8% higher efficacies for sapphire vs PCA lamps depending upon the quality of the PCA and its surface treatment 3). 

Molten zones are also formed by radiant heating (71). The light source may be focused carbon arcs, xenon lamps, sunlight, or lasers. Very high temperatures have been achieved with all of these. For example, sapphire has been float-zoned in this manner, at over 2000°C. 

Halogen lamp, (2) elliptical reflector, (3) sapphire window welded at the center of the bottom of the high-pressure reactor, (4) the assembled sample, (5) high-pressure reactor. Turquoise dashed line shows the alignment of light beam and sample center. 

Historically, this has been the most constrained parameter, particularly for confocal laser scanning microscopes that require spatially coherent sources and so have been typically limited to a few discrete excitation wavelengths, traditionally obtained from gas lasers. Convenient tunable continuous wave (c.w.) excitation for wide-held microscopy was widely available from filtered lamp sources but, for time domain FLIM, the only ultrafast light sources covering the visible spectrum were c.w. mode-locked dye lasers before the advent of ultrafast Ti Sapphire lasers. 

For visual observation of the cell interior through the sapphire windows a lamp mounted behind one end is used. A mirror and stereo microscope at the other end facilitate the observation. The microscope is equipped with a normal camera or a video camera. Normally the phenomena within the cell are continuously observed and controlled with video camera and colour monitor. A video recorder serves for documentation, for inspection of short time processes and for the production of standing flame pictures for size and shape determination. Instead of the microscope a Jarrell-Ash diode array rapid scan spectrometer can be attached to the cell to obtain flame spectra in the visible and UV-regions. 

Experimental. All photodimerizations were carried out in a stainless steel fixed volume cell (1.75 cm ID with a 1.0 cm path length) with sapphire windows under the irradiation of a Hanovia medium pressure mercury lamp filtered through water and Pyrex for a 13.5 hour exposure. The cell and lamp assembly have been described previously (31). For selected runs a custom built 0.9 mL variable-volume pump was connected to the cell and the pressure was varied to determine the exact location of the phase boundary, based on light scattering measured in a Cary 2290 UV-Vis spectrophotometer (Varian Inst.). The spectrophotometer was also used to measure the concentrations of the monomeric cyclohexenone before and after reaction. 

An interesting example of the use of the flash technique with solutions is found in studies by Grossweiner and Matheson135 with iodides. By the use of a sapphire flash lamp, which emits wavelengths shorter than one made of quartz, the iodide ion can be shown to undergo the reaction... 

Due to its relevance to the next section, we observed and analyzed the fluorescent emission of Tryptophan in water solution excited by one, two, and three-photon absorption. For that, three different light sources were used a UV (180-375 nm) lamp, the second harmonic of a Q-switched Nd YAG laser (with 8 ns pulse duration at 532 nm) and a Ti-Sapphire laser delivering pulses at 76 MHz, with 150 fs pulse duration and 500 mW average power at 800 nm. 

The 1849A resonance line from the low-pressure mercury lamp has already been referred to (p. 41). Suprasil or sapphire windows allow the transmission of this line or alternatively the lamp may be placed inside the RV . The intensity of the... 

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