In this work, we report the theoretical results of the single beam transmittance of an absorber by employing the rate equation approach, utilizing 10 ns laser pulses. With the appropriate choice of lifetimes of the participating levels in the transition and their corresponding absorption cross-section, it is possible to control the onset of different phenomena like saturable absorption, reverse saturable absorption, and double saturable absorption. We discuss how to increase the saturable and optical limiting nature of the system by appropriate changes of spectroscopic parameters. We discuss the estimation of spectroscopic terms from their contribution in the single beam transmittance.
Nanoparticles of Titanium dioxide [Formula: see text] with its unique optical and electronic characteristics is an important material for photochemical catalysis. The efficiency of catalytic activity of [Formula: see text] anatase nanostructures is greatly influenced by the photo-generated bound excitons. It is found that the interaction of bound excitons generated in [Formula: see text] enhances the cubic nonlinearity of the system due to strong oscillation of photo-generated bound excitons. The trapped electron hole pair concentration is directly proportional to the photocatalytic efficiency of the [Formula: see text] anatase nanostructures. In our report, we show how these photo-generated bound excitons play a significant role in origin of third-order optical nonlinearities. In particular, we have measured large phase shift and seen two photon absorption process through closed and open aperture Z-scan, respectively, using femtosecond pulses at 532[Formula: see text]nm.
We demonstrate, for the first time to the best of our knowledge, the direct generation of higher-order Laguerre–Gaussian (LG) petal modes, formed of the coherent superposition of positive and negative LG modes with the topological charge of
±
ℓ
as an eigen mode, from a compact diode end-pumped
P
r
3
+
:
L
i
Y
F
4
(YLF) laser with an intra-cavity lens configuration. The on-axis displacement of the intra-cavity lens with spherical aberration allows the selective operation of the desired higher-order LG modes with
|
ℓ
|
≤
31
from the laser cavity at 640 nm and 607 nm. Such visible higher-order LG modes will offer new applications in optical manipulation, quantum/optical underwater telecommunication, and microfabrication.
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