Flashlamps

The first fluorescence lifetime measurements reported using near-IR spark source excitation where performed in the authors laboratory using the all-metal coaxial 

Although nanosecond flashlamps operated in the near-IR possess much less intensity and repetition rate, as well as giving much broader pulses when compared to diode lasers, the recent development of flashlamp operation in the near-IR has 

Price to the introduedon of picosecond lasos, most TCSPC systems used the coaxial fladdamps. A wide range of wavelengths is available, dqwnding on the gas within the fiashlamp. These devices typically provide excitation pulses about 2 ns wide, with much less power than is 

The most significant drawback of using a flashlan ) is the low repetitit rate. The fastest flashlamps have rqieti-tion rates up to lOOkHz, with 20 kHz being more commcm. 

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Pumping is with a flashlamp, as in the case of the ruby laser, and a pulse energy of the order 1 J may be achieved. Frequency doubling (second harmonic generation) can provide tunable radiation in the 360-400 nm region. 

A krypton arc lamp may be used for CW pumping or a flashlamp for much higher power pulsed operation. 

A pulsed dye laser may be pumped with a flashlamp surrounding the cell through which the dye is flowing. With this method of excitation pulses from the dye laser about 1 ps long and with an energy of the order of 100 mJ can be obtained. Repetition rates are typically low - up to about 30 FIz. 

The light source for excitation of Nd YAG lasers may be a pulsed flashlamp for pulsed operation, a continuous-arc lamp for continuous operation, or a semiconductor laser diode, for either pulsed or continuous operation. The use of semiconductor laser diodes as the pump source for sohd-state lasers became common in the early 1990s. A variety of commercial diode-pumped lasers are available. One possible configuration is shown in Figure 8. The output of the diode is adjusted by composition and temperature to be near 810 nm, ie, near the peak of the neodymium absorption. The diode lasers are themselves relatively efficient and the output is absorbed better by the Nd YAG than the light from flashlamps or arc lamps. Thus diode-pumped sohd-state lasers have much higher efficiency than conventionally pumped devices. Correspondingly, there is less heat to remove. Thus diode-pumped sohd-state lasers represent a laser class that is much more compact and efficient than eadier devices. 

Dye-Sensitized Photoisomerization. One technological appHcation of photoisomerization is in the synthesis of vitamin A. In a mixture of vitamin A acetate (all-trans stmcture) and the 11-cis isomer (23), sensitized photoisomerization of the 11-cis to the all-trans molecule occurs using zinc tetraphenylporphyrin, chlorophyU, hematoporphyrin, rose bengal, or erythrosin as sensitizers (73). Another photoisomerization is reported to be responsible for dye laser mode-locking (74). In this example, one metastable isomer of an oxadicarbocyanine dye was formed during flashlamp excitation, and it was the isomer that exhibited mode-locking characteristics. 

Dye lasers, which can lase in either pulsed or CW formats. They may be pumped by flashlamps or by other lasers such as copper vapor, argon ion or by frequency doubled Nd YAG lasers. 

Sum-frequency mixing of two solid-state YAG lasers in a nonlinear crystal (see Ch. 20) to generate 589 nm in CW, CW mode-locked and macromicro pulse formats. The Nd YAG lasers can be pumped by flashlamps, but higher efficiency is obtained using diode lasers. 

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. 

The 6 Nd YAG lasers pump the DM0, preamplifier and power amplifier (Fig. 19, Friedman et al., 1998). The YAG lasers are built from commercially available flashlamp/laser rod assemblies, acousto-optic Q-switches and frequency doubling crystals (LBO and KTP). Most of the mirror mounts and crystal holders are commercial. Nd YAGs are frequency doubled to 532 nm using a nonlinear crystal. The Nd YAG rod and nonlinear crystal are both in the pump laser cavity to provide efficient frequency conversion. The 532 nm light is coupled out through a dichroic and fed to multimode fibers which transport the light to the DM0 and amplifier dye cells. 

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... 

Alster TS,McMeekin TO (1996) Improvement of facial acne scars by the 585 nm flashlamp-pumped pulsed dye laser. J Am Acad Dermatol 35 79-81... 

Manusciatti W, Fitzpatrick RE, Goldman MP (2000) Treatment of facial skin using combinations of CO Q-switched alexandrite, flashlamp-pumped pulsed dye, and Er YAG lasers in the same treatment session. Dermatol Surg 26 114-120 Jordan R, Cummins C, Burls A (2000) Laser resurfacing of the skin for the improvement of facial acne scarring a systematic review of the evidence. Br J Dermatol 142 413-423... 

Pulsed field gel electrophoresis, 9 746 Pulsed flashlamps, 14 619 Pulsed laser deposition chamber, 24 739 Pulsed laser deposition (PLD), 24 738-743 advancement of, 24 739 as an alternative deposition technique, 24 742-743... 

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