I see that many papers based on film random lasers (like polymer films) show very low lasing threshold compared to colloidal random lasers (like rhodamine6G based ones). Is this true in every case, or is it dependent on pump laser pulse width and the repetition rate.
Dear
If changing the concentration of dye or NPS, the lasing threshold also is changing, now change the type of dye but use the same first concentration, also lasing threshold is change. Observe lasing threshold is related to the properties of material use as active medium . pulse duration is effective in lasing process but not on lasing threshold and PRR is not effective on lasing process.
Regard
Dr.jassim
It seems, Mr. Venkata`s question is another, i.e. is the threshold of film random lasers always lower, than for colloidal random lasers, or it depends on parameters of pump pulse ?
1. I think, for each type of active material, threshold, of course, will depend on pump pulse duration (for long pulses of the same energy you will not reach threshold).
2. As random lasing, in the first turn, depends on light scattering properties of active material, we can not say apriory, where threshold will be lower, because formation of nanoscale scattering structures could be performed in very different materials, not only in polymer films or colloidal systems. Supposing the same decay time of dye in films and colloidal system, relation between threshold value of these systems will not depend on pulse duration. But, if decay time is very different (I don`t know these data) - will depend.
3. PRR will effect on characteristics of each laser through thermal effects - average heating, thermal gradients, etc. Anyway, to say more exactly, we must consider exact type of random laser. PRR effects can be large or smaller, but they will always exist.
In conventional lasers, the optical cavity that confines the photons
also determines essential characteristics of the lasing mo
des such as wavelength, emission pattern, directivity, and polarizat
ion. In random lasers, which do not have mirrors or a well-defined cavity,
light is confined within the gain medium by means of multiple scattering. The sharp peaks in the emission spectra of semiconductor powders,
first observed in 1999, has therefore lead to an intense debat
e about the nature of the lasing modes in these so-called lasers with
resonant feedback.cavity modes of a conventional laser and produce sharp lasing peaks. Random lasers are disordered media with gain that do not possess a light-trapping cavity beyond the confinement provided by multiple-scattering from the disorder itself. Hence they are usually extremely open, low finesse lasers. Initially it was unclear whether such systems could produce narrow lasing lines without any well-confined electromagnetic modes, and while initial experimental studies did find strong amplification near the transition frequency determined by the gain medium, discrete lines were not observed.
P. W. Anderson, “Absence of Diffusion in Certain Random Lattices,” Phys. Rev.109, 1492 (1958).
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