Energy density, of lasers

The energy densities of laser beams which are conventionally used in the production of thin films is about 10 — 10 Jcm s and a typical subsU ate in the semiconductor industry is a material having a low drermal conductivity, and drerefore dre radiation which is absorbed by dre substrate is retained near to dre surface. Table 2.8 shows dre relevant physical properties of some typical substrate materials, which can be used in dre solution of Fourier s equation given above as a first approximation to dre real situation. 

Fig.4. Experimental (heavy lines) and computer calculated (light lines) melt depths as a function of time for several energy densities of laser pulses. ...

Figure 5 CL spectra of uHrahigh vacuunn-cleaved CdS before and after in situ deposition of 50 A of Cu, and after in situ laser annealing using an energy density of 0.1J /cm. The electron-beam voltage is 2 kV. ...

Fig. 19.5 The spectral position of the laser emission and the threshold curves (in the insets) for (a) an etched resonator with OD 75 pm and the wall thickness of 3.8 pm having threshold at pump energy density of 1 pj/mm2 and (b) unetched resonator with OD 75 pm and the wall thickness of 5 pm with a threshold of 25 nJ/mm2. Reprinted from Ref. 20 with permission. 2008 International Society for Optical Engineering...

The energy density of the laser irradiation required to melt the dye and to induce diffusion will be given by ... 

Solution Phase Studies. Freshly prepared solutions were used for all experiments. All solution phase studies were carried out using samples which had been thoroughly de-gassed using a minimum of three freeze-pump-thaw cycles for each sample, lire final pressure above the sample was in all cases less than 5 x 1(H mBar. Laser energy densities of less than 2.5 mJ cm-2 were used such that sample degradation was kept to a minimum. 

Pulsed laser deposition (PLD) [1-3] uses high-power laser pulses with an energy density of more than 108 W cm 2 to melt, evaporate, excite, and ionize material from a single target. This laser ablation produces a transient, highly luminous plasma plume that expands rapidly away from the target surface. The ablated material is collected on an appropriately placed substrate surface upon which it condenses and a thin film nucleates and grows. 

Evaporation and redeposition of carbon occur at the very first moment upon laser excitation. During light emission, no further changes are observed. The laser heats and evaporates carbon black, reaching temperatures of >3,000°C within the focal point of the beam. Carbon material around the focus spot is heated too, but the energy density of the laser is insufficient to reach the evaporation temperature. 

Fig. 12.9 PL and second-order DFB laser spectra for different grating periods for neat thin films of Spiro-60T (a) Spiro-DPVBi (b). The laser threshold energy densities of the neat guest, neat host and an optimized G-H system are compared (c).

Modification of Ge nanoclusters in Si matrix by ruby laser pulses has been studied. Energy density of irradiation was near melting threshold of Si surface. The decrease of the nanocluster in size and the partial relaxation of stresses are observed. More considerable changes occur by multipulse irradiation. Ge nanoelusters are transformed into the clusters of Ge Sii-x solid solution. 

Figure 11.3 schematically shows the experimental setup. The approach consists of a pulsed nozzle, skimmer, and reflectron TOF mass analyzer. The 125 nm VUV beam was introduced along the jet axis and focus in the ionization volume. A doubled NdiYAG laser (532 nm) was used for desorption, with pulse energy densities of 10 to 100 mj /cm and a spot size of about 1 mm diameter. Vaporization was caused by substrate heating only. Optimal injection of the vapor into the jet expansion occurred when the desorption spot was about 1 mm in front of and 0.5 mm below the nozzle, and the desorption laser was fired near the peak of the jet gas pulse. The pulsed valve was operated with Ar or Xe at a backing pressure of 8 atmospheres. 

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