Efficiency of lasers

Although phenomenological and simplistic, these simulations show that the efficiency of laser triggering and guiding may be improved by orders of magnitude, provided the laser shots are triggered by electric activity in thunderclouds and kept oriented towards the most active regions of the clouds. 

Concerning the Ka yield, the experimental works published in the last years showed a conversion efficiency of laser energy to Ka photons of 10 4-10-5, leading to a total number of 109-1010 Ka photons per joule of laser energy for each driving laser shot. As an example, Fig. 9.5 from [66] shows... 

Figure 1. Diagram of the intensity / (W/cm2) vs. duration of laser pulse tp(s) with various regimes of interaction of the laser pulse with a condensed medium being indicated very qualitatively. At high-intensity and high-energy fluence 4> = rpI optical damage of the medium occurs. Coherent interaction takes place for subpicosecond pulses with tp < Ti, tivr. For low-eneigy fluence (4> < 0.001 J/cm2) the efficiency of laser excitation of molecules is very low (linear interaction range). As a result the experimental window for coherent control occupies the restricted area of this approximate diagram with flexible border lines.

The laser-initiated polymerization of styrene with maleic anhydride has been said to occur through either a singlet or triplet excimer (the authors surely mean exciplex ) of the anhydride as shown in Scheme 4. This study provides an interesting comparison between laser- and u.v.-initiated polymerization, and Table 2 shows clearly that the former is a very energy-efficient system. In the laser-initiated polymerization of a thiol-ene system, oxygen inhibition was not a significant problem and similar conclusions were reached on the energy efficiency of lasers. On a related note, the efficiency of the well-known benzo-phenone-triethylamine complex is apparently enhanced if carboxylic acids are added to the system. ... 

In contrast to the previous case, there are examples where thermal conduction clearly limits the efficiency of laser removal techniques. For in-... 

Horn, I., Gunther, D. (2003) The influence of ablation carrier gasses Ar, He and Ne on the particle size distribution and transport efficiencies of laser ablation-induced aerosols implications for LA-ICP-MS. Applied Surface Science, 207,144-157. 

The volume of the laser ablation sample cell, the geometry, the type of carrier gas and its flow pattern, and the tubing properties of the transfer line to transport the aerosol into the ICP are all together important factors that contribute to the total transport process and the transient signal structure. The transport efficiency of laser-induced particles therefore restricts the detection ca-pabihties for laser ablation microanalysis. Any enhancement in the transport process will make it possible to decrease the laser spot size and still detect a signal from the ablated mass, and therefore wih lead to an increase of the spatial resolution that can be successfully used for laser ablation. 

The efficiency of gas turbines is limited by the maximum allowable turbine inlet temperature (TIT). The TIT may be increased by cooling of the blades and vanes of the high pressure turbine. Cooling channels can be casted into the components or may be drilled afterwards. Non-conventional processes like EDM, ECD or Laser are used for drilling. Radiographic examination of the drilled components is part of the inspection procedure. Traditional X-Ray film technique has been used. The consumable costs, the waste disposal and the limited capacity of the two film units lead to the decision to investigate the alternative of Real-Time X-Ray. 

It has been said tliat anytliing will lase if pumped witli enough energy, but tire efficiency of tire pumping process is important for practical, economical devices. In tliis regard two-level lasers are of little interest because, except under extraordinary pumping conditions, one can only equalize tire populations of tire upper and lower levels. A... 

A wide variety of metliods has been used to pump laser systems. Altliough optical pumping has been implied, tliere is an array of collisionally or electron impact pumped systems, as well as electrically pumped metliods. The efficiency of tire pumping cycle in many ways defines tire utility and applications of each scheme. The first... 

The He-Ne laser system was the first efficient CW laser. It is still one of the most common systems in use today. 

These data are typical of lasers and the sorts of samples examined. The actual numbers are not crucial, but they show how the stated energy in a laser can be interpreted as resultant heating in a solid sample. The resulting calculated temperature reached by the sample is certainly too large because of several factors, such as conductivity in the sample, much less than I00% efficiency in converting absorbed photon energy into kinetic energy of ablation, and much less than 100% efficiency in the actual numbers of photons absorbed by the sample from the beam. If the overall efficiency is 1-2%, the ablation temperature becomes about 4000 K. 

The efficiency of a ruby laser is less than 0.1 per cent, typically low for a three-level laser. 

A further advantage is the higher efficiency of the alexandrite laser because of its being a four-level laser. In the illustration in Figure 9.2(c), level 4 is a vibronic level and level 3 the zero-point level of the T2 state. Level 2 is a vibronic level of the 2 state and level 1 the zero-point level. Because of the excited nature of level 2 it is almost depopulated at room... 

Semiconductor lasers are some of the most efficient of all lasers, with an efficiency of abouf 30 per cenf. 

The CO2 laser is a near-infrared gas laser capable of very high power and with an efficiency of about 20 per cent. CO2 has three normal modes of vibration Vj, the symmetric stretch, V2, the bending vibration, and V3, the antisymmetric stretch, with symmetry species (t+, ti , and (7+, and fundamental vibration wavenumbers of 1354, 673, and 2396 cm, respectively. Figure 9.16 shows some of the vibrational levels, the numbering of which is explained in footnote 4 of Chapter 4 (page 93), which are involved in the laser action. This occurs principally in the 3q22 transition, at about 10.6 pm, but may also be induced in the 3oli transition, at about 9.6 pm. 

The efficiency of a helium—neon laser is improved by substituting helium-3 for helium-4, and its maximum gain curve can be shifted by varying the neon isotopic concentrations (4). More than 80 wavelengths have been reported for pulsed lasers and 24 for continuous-wave lasers using argon, krypton, and xenon lasing media (111) (see Lasers). 

Free-Electron Lasers. The free-electron laser (EEL) directly converts the kinetic energy of a relativistic electron beam into light (45,46). Relativistic electron beams have velocities that approach the speed of light. The active medium is a beam of free electrons. The EEL, a specialized device having probably limited appHcations, is a novel type of laser with high tunabiHty and potentially high power and efficiency. 

The two-dimensional carrier confinement in the wells formed by the conduction and valence band discontinuities changes many basic semiconductor parameters. The parameter important in the laser is the density of states in the conduction and valence bands. The density of states is gready reduced in quantum well lasers (11,12). This makes it easier to achieve population inversion and thus results in a corresponding reduction in the threshold carrier density. Indeed, quantum well lasers are characterized by threshold current densities as low as 100-150 A/cm, dramatically lower than for conventional lasers. In the quantum well lasers, carriers are confined to the wells which occupy only a small fraction of the active layer volume. The internal loss owing to absorption induced by the high carrier density is very low, as Httie as 2 cm . The output efficiency of such lasers shows almost no dependence on the cavity length, a feature usehil in the preparation of high power lasers. 

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