Flashlamp-pumped systems

If we look at a few cases In the literature, we see a wide variation In the reported limiting noises [2A-27]. Table IV lists noises and detection limits for several laser systems. A flashlamp-pumped system, because of the relatively low Intensity and wide temporal pulse width, about 1 /is. Is limited by flame emission shot and flicker, which are temporally continuous noises. The... 

Lick Observatory. The success of the LLNL/AVLIS demonstration led to the deployment of a pulsed dye laser / AO system on the Lick Observatory 3-m telescope (Friedman et al., 1995). LGS system (Fig. 14). The dye cells are pumped by 4 70 W, frequency-doubled, flashlamp-pumped, solid-state Nd YAG lasers. Each laser dissipates 8 kW, which is removed by watercooling. The YAG lasers, oscillator, dye pumps and control system are located in a room in the Observatory basement to isolate heat production and vibrations from the telescope. A grazing incidence dye master oscillator (DMO) provides a single frequency 589.2 nm pulse, 100-150 ns in length at an 11 kHz repetition rate. The pulse width is a compromise between the requirements for Na excitation and the need for efficient conversion in the dye, for which shorter pulses are optimum. The laser utilizes a custom designed laser dye, R-2 perchlorate, that lasts for 1-2 years of use before replacement is required. 

Experimental reseach directed toward discovery of new RPLs has continued at the University of Illinois. System studies of possible large-scale RPL applications and detailed measurements of radiation-induced absorption in optical materials have been reported. Concepts for using nuclear-pumped flashlamps for industrial applications and for laser excitation have been explored [Prelas (1995)], and the first nuclear-flashlamp-pumped laser (iodine at 1.31 micron) has been reported. 

The Na + system has been chosen both for theoretical and experimental reasons. Ab initio potential energy surfaces are available /3/ and trajectory calculations are currently performed. CARS has been used to measure the state distribution of in photolysis /4/ and reaction dynamics /5/. Fig. 1 shows our experimei al setup. In a probe cell we produce a gas mixture of Na (550 K, 10 torr) and (10 to 1000 torr). A flashlamp-pumped dye laser (FLP) with variable pulselength excites sodium to the 3P-state. A CARS laser system detects the rovi-br gic population of hydrogen. Our present sensitivity is approximately 10 particles per cm and quantum state. With an adjustable time control the CARS laser system can monitor the requested population before, during or after the irradiation of the FLP-laser with a time resolution of 10 ns. 

The pump lasers were designed and built at LLNL. Two laser cavity configurations are employed. Two "L" shaped cavities run at the full system repetition rate of 26 kHz, producing 40-50 W per laser. They pump the DM0 and preamplifier dye cells. Four "Z" cavity lasers run at 13 kHz, each producing between 60-80 W. They are interleaved in the power amplifier dye cell to produce an effective 26 kHz repetition rate. Flashlamps were used to pump the frequency-doubled YAG lasers as diode-pumps were much more expensive at the time the Keck LGS was designed. In addition, high wavefront quality is not required... 

There are many solid state lasers. One of the most commonly treated types in laser textbooks is the ruby laser (Al203 Cr +), which was the first laser system demonstrated by T. H. Maiman at the Hughes Research Laboratory early in 1960 (Maiman, 1960). Figure 6.9 in Chapter 6 will show the quantum energy levels associated with the unfilled 3d inner shell of the Cr + ion when it substitutes for the AP+ ion in the AI2O3 lattice crystal. By using a ruby rod placed inside a spiral flashlamp filled with a hundreds of torrs of xenon, it is possible to optically pump Cr + ions from the " A2g ground state into the broad " T2 and " Ti bands of the excited levels. After a rapid relaxation down to the very sharp Eg level, laser emission can be produced at 694 nm via the Eg " A2g transition. 

A chemically pumped CO2 laser oscillating at 10 p was reported by GrossIn this system vibrationally excited COj molecules are produced by inelastic collisions with vibrationally excited DF which was formed by ultraviolet photolysis of a F2O-D2 mixture with a Xe flashlamp, producing free fluorine atoms which could react with Dj... 

In a solid state laser, the active species is distributed throughout a solid, usually crystalline, material, although glass can also be used as a host. The lasers are robust and frequently tunable, though heat dissipation can sometimes be an issue. Certain types of solid state crystals, for example neodymium-doped yttrium aluminum garnet (Nd YAG), can be pumped by diode lasers instead of by other lasers or by flashlamps, which is often the case for other materials. Such diode-pumped, solid state systems are reliable, economical, compact, and easy to operate—in fact, many commercial systems are turnkey, needing only to be plugged in and turned on to operate. 

A flashlamp-, nitrogen laser-, or Nd YAG laser-pumped dye laser system may be used for LEI, keeping in mind the tradeoffs. Excimer laser-pumped dye laser systems should also be suitable. Realistically, availability may be the most compelling factor in choosing a laser. 

Fig. 23. Experimental set-up of the Gwatt photochemical iodine laser (a). The pulsecutting system after the oscillator consists of a Pockels cell and Gian prism. The Pockels cell is switched by a spark gap which is triggered by the laser light deflected from the prism. Gain can be measured by the diodes Di.Dg. The duration and sequencing of the flashlamp pulses for pumping the three stages and the switching time of the oscillator are indicated in part (b) of the figure...

Another useful laser material is Nd YLF (Yttrium-Lithium—Fluoride). The upper state fluorescent lifetime in YLF is about 520 lis as compared with about 230 is for YAG, which makes Nd YLF particularly valuable for high-repetition systems (kHz), which can then be efficiently pumped by a GW discharge lamp rather than a flashlamp. After frequency doubling to 527 nm such systems can yield 20mJ/pulse at 1 kHz, averaging a power in the green of 20 W. 

Rare earth laser action has been obtained for two groups of liquids metallo-organic and inorganic aprotic liquids. The first group are chelate lasers and are reviewed by Lempicki and Samelson (1966) research on aprotic materials and systems for high-power, pulsed liquid lasers are reviewed by Samelson and Kocher (1974). Stimulated emission in both liquids occurs between 4f states of trivalent rare earths. Optical pumping is via xenon-filled flashlamps in optical cavities and resonators similar to those used in solid-state lasers. Rare earth liquid lasers have only been operated pulsed. 

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