Pulsed operation

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

The Nd YAG rod is a few centimetres long and contains 0.5 to 2.0 per cent by weight of Nd. In pulsed operation the peak power of each pulse is sufficiently high for generation of second, third or fourth harmonics at 533 nm, 355 nm and 266 nm, respectively, using suitable crystals. 

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. 

A commercial fs-laser (CPA-10 Clark-MXR, MI, USA) was used for ablation. The parameters used for the laser output pulses were central wavelength 775 nm pulse energy -0.5 mj pulse duration 170-200 fs and repetition rate from single pulse operation up to 10 Hz. In these experiments the laser with Gaussian beam profile was used because of the lack of commercial beam homogenizers for femtosecond lasers. 

The differential-pulse operation results in a very effective correction of the charging background current. The charging-current contribution to the differential current is negligible, as described by... 

Kirtland, B.C. and Aelion, C.M., Petroleum mass removal from low permeability sediment using air sparging/soil vapor extraction impact of continuous or pulsed operation, J. Contam. Hydrol., 41, 367-383, 2000. 

If, however, the effect is truly based on the cavitation chemistry, then cavitation must be provided during the transformation itself either operated in continuous manner or in suitable pulsed operation. The scientific database from the laboratory... 

Pulse operation (80) is an alternative mode with a flow reactor, and is particularly convenient for use with reactants which are only available in very small quantities (e.g. 13C-labeled substances). It also has the advantage that the pulse of reaction products may, if desired, be passed directly to a GPC column for analysis. 

The pulsed operation of the gas-filled detector illustrates the principles of basic radiation detection. Gases are used in radiation detectors since their ionized particles can travel more freely than those of a liquid or a solid. Typical gases used in detectors are argon and helium, although boron-triflouride is utilized when the detector is to be used to measure neutrons. Figure 5 shows a schematic diagram of a gas-filled chamber with a central electrode. 

Some lasers produce a continuous-wave (CW) beam, where the timescale of the output cycle is of the same order as the time taken to remove photons from the system. CW lasers can be modified to produce a pulsed output, whereas other lasers are inherently pulsed due to the relative rates of the pumping and emission processes. For example, if the rate of decay from the upper laser level is greater than the rate of pumping then a population inversion cannot be maintained and pulsed operation occurs. 

Another issue is the membrane buckling due to internal and thermal stress of the CMOS layers, which are not optimized for high-temperature operation. The buckling of the microhotplate can generate severe problems in the adhesion of the sensitive layer. In a temperature-pulsed operation mode, the repeated bending of the membrane could cause a rehabihty problem [120]. 

M. Jaegle, J. WoUenstein, T. Meisinger, H. Bottner, G. Muller, T. Becker, and C. Bosch-von Braunmilhl. Micromachined thin film Sn02 gas sensors in temperature-pulsed operation mode . Sensors and Actuators B57 (1999), 130-134. 

Compact and stable devices are available that take advantage of the improved quality of the crystal lasers, as well as increased pump efficiencies. Hundreds of different models of Nd + based lasers have demonstrated laser action (Kaminskii, 1981). It is possible to operate these Nd + solid state lasers in the continuous regime, with output powers ranging from 1 W to 1000 W. Pulsed operation is also possible, with a pulse length from the picosecond range, via mode-locking, to tens of nanoseconds by Q-switch operation. 

This type of pulse operation should not be confused with duty cycle as used in medical ultrasound. In medical parlance the duty cycle refers to the on/off ratio for scanning which involves the emission of pulse of extremely short duration (e. g. 10" seconds) involving only a few cycles of ultrasound in the MHz range. It is in the longer off period that the echoes are detected. By way of contrast a chemical sonicator pulse of 0.5 s involves 10000 cycles at 20 kHz. 

Bhaumik et al. also examined the operation of a 1P21 phototube under pulsed operation. They found that the gain at 2.5 kV was more than a factor of 250 higher than at 1 kV. They concluded that the dark current... 

Specimens of catalysts (0.125 gram) were deactivated at 360° C for desorption experiments by using continuous (rather than pulsed) operation. Purified liquid benzene or cumene was pumped to the injection port of the microreactor system with a syringe pump at the rate of 0.00241 moles/hour. Propylene was fed from a gas lecture bottle through a rotameter at a rate of 0.00245 moles/hour. Parent H-mordenite catalyst samples were de-... 

---