Q-switched mode

Q-switched mode, ie, pulse duration are on the order of a few tens of nanoseconds and peak power in excess of 10 W. 

A laser-initiated pyrotechnic system (Zr-Amm perchlorate) for spacecraft application has been shown to be superior to conventional electroexpl initiation (Ref 22). Primary high expls such as LA and LSt can be initiated directly. Q-switched-mode lasers can directly deton PETN, RDX, and Tetryl in a properly designed device and can be useful where microsecond simultaneity is important (Ref 6)... 

It was found that when the laser is operated in the Q-switched mode, the droplet (Propyl-nitrate or heptane) appears to break up or evaporate without ignition however, a blast wave due to energy addition via gaseous break down is always present. When the laser is operated in the pulsed mode with two pulses at 100 nsec apart, the first pulse serves to break up the drop and the second to ignite it. In this case explosive combustion is often observed in oxygen whereas a non-explosive ignition takes place if air is used. ... 

Experimental Apparatus. Figure 1 shows a block diagram of the apparatus used in these experiments. A Q-switched, mode-locked... 

Figure 1. Q-switched, mode-locked Nd YAG laser with two synchronously pumped dye lasers PC = Pockels cell POL = polarizer with escape window DLl, DL2 = cavity dumped dye lasers PMT = photomultiplier tube. (Reproduced from Ref. 7. Copyright 1986 American Chemical Society.)...

A schematic representation of the directed-beam laser writing scheme is shown in Figure 1. Although a carbon dioxide or excimer gas laser can be used, the most common laser used for directed-beam writing is the solid state YAG laser operated in the cw Q-switched mode. With typical laser powers of about 20 watts average power and a pulse repetition rate of 20,000 pulses per second, the laser beam when focused on the sample makes a small (about 0.1 mm diameter) dot for each pulse. By directing the laser beam using fast computer-driven mirrors... 

With a front face-pumped compact active-mirror laser (CAMIL) structure, an Yb YAGAY AG composite ceramic disk laser with pumping wavelength at 970 run has been reported [210]. The laser was operated in both CW and Q-switching modes. Under CW operation, laser output power of 1.05 W with 2 % transmission OC was achieved at the wavelength of 1031 nm. Q-switched laser output was obtained by using an acousto-optic Q-switch, with repetition rates of 1-30 kHz and pulse widths of 166-700 ns. 

Figure 3.11 Time evolution of population inversion, loop gain and laser output for a laser operating in normal-pulse mode (left) and Q-switched mode (right). An expanded view of the Q-switched region is shown on the right...

Measurements were made of the concentration profiles of A1 atoms which had been introduced into p-type material by irradiation with a Nd YAG laser in the continuous wave or Q-switched modes. It was found that limiting concentrations of A1 atoms in the Si substrate were attained during irradiation under continuous wave conditions. The concentrations which were measured under irradiation in the Q-switched mode... 

The lasers we have considered so far have a solid material as the active medium. Generally, flash-lamp pumping is employed and short pulses are obtained at a repetition rate of typically 10 Hz. High peak powers are obtained in the Q-switched mode (MW-GW). Gaseous media can also be used for the generation of short laser pulses. We shall here consider the nitrogen laser, the excimer laser and the copper vapour laser. The relevant parts of... 

The reaction centers are isolated from the carotenoid-less mutant of Rhodobacter sphaeroides and purified using a DEAE cellulose column. The sample solution (OD-30 at 355 nm) is circulated by a mechanical pump through an 3Q0 /im (ID) glass nozzle to form a liquid jet. The temperature of the sample is kept at 10 C. The third harmonic (355 nm) output of a Q-switched, mode-locked Nd YAG laser is used to generate RR scattering with powers in the 5-30 mW range. The... 

Many types oflasers are used for this analysis technique, including Nd-YAG, ruby, CO2, N2, and excimer. For satisfactory operation, lasers must be capable of sufficient power density to effectively ablate and vaporize refractory sample matrices. Both the Nd-YAG and ruby lasers can be operated in two modes normal (free-running) mode and the fixed Q-switched mode. In the normal mode, ablation craters are created with uniform and reproducible diameters, the depth of which are determined by the number of pulses used. The Q-switched mode is used for samples that are particularly difficult to energy couple because of their transparent nature. Although the Q-switched mode provides more energy and hence a larger amount of material is ablated, performance in terms of efficiency and reproducibihty are usually not a good as operation in the normal mode. 

---