Search

Highly efficient broadband absorbing surfaces covering the UV, visible and near-IR regions are of great importance for low-light imaging devices, optical devices and optoelectronic devices. In this work, we demonstrate the fabrication of remarkably efficient absorbing surfaces due to the formation of nanoflower-like cavity structures on a stainless steel (SS304) surface, along with micropatterning in a hierarchical fashion. The fabrication process is carried out using noncontact, programmable, single-step laser irradiation by an inexpensive and robust 532 nm nanosecond laser. The measured specular antireflection properties over a wide spectral region (250-1800 nm) are extremely low, less than 0.5%, over a large range of incident angles and for both orthogonal polarizations. These special hierarchical structures with nanorods, nanoparticles, and nanocavities, completely trap the photon incident on these surfaces due to multiple reflections. These surface structures evolve with time to give better nanostructured features with higher oxygen content on the surfaces, revealed by FESEM elemental analysis, which increases the ability to trap photons. We believe these antireflection surfaces, with high efficiencies and long-term stability, will play a vital role in many modern technological applications.

44th Annual Laser Damage Symposium on Laser-Induced Damage in Optical Materials, Natl Inst Stand & Technol (NIST), Boulder, CO, SEP 23-26, 2012; International audience; We investigated formation of defects in four polymers namely Poly (methylmethacrylate) [PMMA], Poly dimethylsiloxane [PDMS], Polystyrene [PS], and Polyvinyl alcohol [PVA] and crystal media such as Lithium Niobate [LiNbO3]. Spectroscopic studies of the femtosecond (fs) laser modified regions were systematically performed after fabricating several gratings and micro-channels. We observed emission from the fs laser modified regions of these polymers when excited at different wavelengths. Pristine polymers are not paramagnetic, but exhibited paramagnetic behavior upon fs irradiation. LiNbO3 (LNB) crystal has not shown any defect formation upon laser irradiation. Confocal micro-Raman studies were also performed to establish the formation of defects.

Laser-induced ripples or uniform arrays of continuous near sub-wavelength or discontinuous deep sub-wavelength structures are formed on single-crystalline silicon (Si) by femtosecond (fs) laser direct writing technique. Laser irradiation was performed on Si wafers at normal incidence in air and by immersing them in dimethyl sulfoxide using linearly polarized Ti:sapphire fs laser pulses of ∼110 fs pulse duration and ∼800 nm wavelength. Morphology studies of laser written surfaces reveal that sub-wavelength features are oriented perpendicular to laser polarization, while their morphology and spatial periodicity depend on the surrounding dielectric medium. The formation mechanism of the sub-wavelength features is explained by interference of incident laser with surface plasmon polaritons. This work proves the feasibility of fs laser direct writing technique for the fabrication of sub-wavelength features, which could help in fabrication of advanced electro-optic devices.

Silver nanostructures were fabricated by laser direct writing technique using 796-nm Ti:Sapphire fem- tosecond laser pulses in polymer matrix containing silver ions that has been spin coated on a silicon substrate. Silver nanostructures that resulted inside the polymer matrix were obtained by the nonlinear optical interaction between femtosecond laser pulses and polymer films containing silver ions. We report here the characterization of the silver nanostructures using UV-Vis extinction spectra, field emission scanning electron, and atomic force microscope images. Formation of silver nanoparticles inside the laser written microstructures is confirmed by the appearance of surface plasmon absorption band at 448 nm in the UV-Vis extinction spectrum. Nanoparticles formed were spherical in shape with average particle size

Nonlinear absorption, 1D self-focusing and 1D self-trapping of optical beams are studied in 150 ppm Fe-doped Bi 12 SiO 20 crystal using single beam Z-scan technique in nano second regime using coherent and incoherent laser pluses with out applying any external electric field across the crystal. When the crystal is placed in expanding beam 1D self-trapping is observed due to 1D self-focusing. The nonlinear absorption is also observed at high intensities due to trap assisted excited state absorption as well as two photon absorption. The ground state absorption and increased nonlinear absorption at 532 nm and 595 nm compared to pure BSO indicates the increased impurity traps in the crystal lattice due to iron incorporation. The studies reveal that incorporation of iron in BSO making it an excellent optical limiter.