Threshold energy density

For a high density optical recording medium, two important parameters which characterize its capability are the size of mark and the threshold energy density required for mark creation. The size of the mark was found to be dependent on both the incident power and the exposure time. The size of the marked areas is shown in Figure 6 for different levels of power and exposure... 

Of particular interest is the pulse duration dependence of the threshold energy density thr for the appearance of mass spectra (Fig. 2) in the case of the multiple-photon UV ionization of the Trp Gly Ala molecule. It is clearly seen that the threshold energy density is reduced by a factor of 10 in the case of irradiation with femtosecond pulses. The same effect is observed with a pure tryptophan powder. The threshold energy density for the appearance of the 300-fs pulse mass spectrum, E%r = 10-3 J/cm2 (3 x 109 W/cm2), is an order of magnitude lower than that of the 15-ns mass spectrum, [ r = 10 2 J/cm2 (6 x 105 W/cm2). 

The dependence of the enhancement on US intensity, pulse length and application time can be combined into a single parameter, namely the total density delivered by the transducer ( = intensity x application time x pulse duration). There is a threshold energy density for skin permeability to be affected, which is approximately 200 J/cm at the applied frequency [119]. 

When there is gasformation with enhance of threshold energy density value strong absorption of laser emission is being observed (see figure 7). 

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).

Fig. 9.56. Upper threshold energy densities eAb as function of the number N of pulses per area and wavelength of the laser used A = 248,308 and 355 nm [67]...

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