Q switching

In order to achieve a reasonable signal strength from the nonlinear response of approximately one atomic monolayer at an interface, a laser source with high peak power is generally required. Conuuon sources include Q-switched ( 10 ns pulsewidth) and mode-locked ( 100 ps) Nd YAG lasers, and mode-locked ( 10 fs-1 ps) Ti sapphire lasers. Broadly tunable sources have traditionally been based on dye lasers. More recently, optical parametric oscillator/amplifier (OPO/OPA) systems are coming into widespread use for tunable sources of both visible and infrared radiation. 

Fig. 4. Temporal pulse characteristics of lasers (a) millisecond laser pulse (b) relaxation oscillations (c) Q-switched pulse (d) mode-locked train of pulses, where Fis the distance between mirrors and i is the velocity of light for L = 37.5 cm, 2L j c = 2.5 ns (e) ultrafast (femtosecond or picosecond) pulse.

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

Metal-free, chloroaluminum phthalocyanine [14154-42-8] vanadyl phthalocyanine [13930-88-6], or magnesium phthalocyanines are sufficiently soluble in organic solvents and show enough bleachable absorption at 694.3 nm to serve as repeated Q-switching elements for mby lasers (qv) (180). Phthalocyanines have been used in other lasers as weU (181). 

A Q-switched, frequency-quadrupled Nd—YAG laser (X, = 266 nm) and its accompanying optical components produce and focus the laser pulse onto the sample surface. The typical laser spot size in this instrument is approximately 2 pm. A He-Ne pilot laser, coaxial with the UV laser, enables the desired area to be located. A calibrated photodiode for the measurement of laser energy levels is also present... 

A series of papers by. Menichelli Yang (Refs 82, 84 86) showed that Q-switched ruby lasers could initiate steady detonation in PETN (and RDX or Tetryl) in <0.5 psec when a lOOOA-thick Al layer was deposited on the face of the sample, and subsequently exposed to laser radiation of 0.5 to 4.2 J with a pulse width of 25nanosec... 

PMMA finds ordn usage in several areas in ballistic or impact shields for missiles or airplanes also as windows, windshields or canopies in aircraft (Refs 7 and 22) as a Laser Q switch host using an organic Ni complex dye (Ref 22) and in proplnts as fuel (with A1 and NG as cofuels — Ref 20) and Amm perchlorate or K perchlorate as oxidizers (Refs 2, 4, 8—11, 13,14 16—20). Also see under Aeroplex Propellants in Vol 1, A108-R and under Composite Propellants in Vol 3, C464-L to C474-L Refs 1) Beil 2, [398] and (1279 1283 ... 

A Q-switched Nd YAG laser (7 ns pulse duration, Quanta-Ray DRC-1A) operated at 10 Hz was used as a light source. The 1064 nm fundamental was frequency doubled to 532 nm for some experiments. In all experiments reported here a geometry was used which focused the laser beam in front of the entrance window of the sample cell such that the laser beam was diverging as it passed through the sample cell. In this geometry the laser beam was about 3 mm in diameter at the region viewed by the light detection system. 

Figure 19. A set of 6 frequency-doubled, Q-switched Nd YAG lasers are used to pump the DM0, preamplifier and power amplifier.

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. 

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... 

Bellew SG, Alster TS (2004) Treatment of exogenous ochronosis with a Q-switched alexandrite (755 nm) laser. Dermatol Surg 30(4 Pt 1) 555-558... 

Fe(6-Mepy)2(py)tren] (004)2 Doped in PSS. Magnetic susceptibilities measured for a microcrystalline sample of the complex produce a magnetic moment value = 0.36 pg at 10 K and 0.61 pg at 150 K, followed by a gradual increase to Peff = 2.80 pe at 311 K [138]. Thus 26% of the complexes are in the HS state at 300 K if a magnetic moment of 5.1 Pe is assumed for the pure HS compound. On the other hand, the complex doped into a polystyrene sulfonate (PSS) film does not provide any evidence for a thermal population of the HS state up to 340 K as demonstrated by variable-temperature UV-VIS and Mossbauer spectra. In fact, all the complexes doped into the PSS film are in the LS state at temperatures below 340 K. However, if irradiated by a single pulse of a Q-switched Nd/YAG laser (532 mp), the complex is excited from the LS ground state to the HS J2 states via an intermediate MLCT state and the metal states. The subsequent back relaxation from the excited T2 state to the... 

For comparison purposes, two other MS systems have been used with in vitro grown parasite cultures. In the first case, a home-built miniaturized linear TOF multi-array analyzer1718 was interfaced to the frequency-tripled output at 355nm of a Q-switched Nd-YAG laser ( Polaris, New Wave Research, Fremont, CA). In this experiment the laser beam was not scanned, and the estimated laser fluence after attenuation was similar to that of the commer-... 

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