Laser-matter interaction is a unique and simple approach to structure materials or locally modify their properties at the
micro and nanoscale level. Playing with the pulse duration and the laser wavelength, a broad range of materials and
applications can be addressed. Direct irradiation of surfaces with laser beam through a standard optical beam setup
allows an easy and fast structuring of these surfaces in the range of few micrometers. However, the irradiation of
materials through an array of dielectric nanospheres provides a unique opportunity to break the diffraction limit and to
realize structures in the range of hundred of nanometers. This simple, fast and low-cost near-field nanolithography
technique is presented and discussed, as well as its great potential.
The theoretical aspects of the near-field enhancement effects underneath the particles have been studied with a simple
model based on the Mie theory. A commercial FDTD software has also been used to study the influence of the substrate
and the surrounding media, on the energy profile of the photonic jet generated under the sphere. A specific study has
been dedicated to the influence of the dispersion of the sphere diameter on the morphology of the ablation craters. This
technique has been used for patterning bi-layer substrates. The process leads to the formation of a nanoporous membrane
which has been used to realize an array of gold nanodots on silicon. We have also associated the Laser-Induced Forward
Transfer (LIFT) process with the near-field nanolithography to print, in a single laser shot, an array of metallic
Laser near-field enhancements underneath transparent microspheres can be used to locally implement new functionalities in materials. Using this technique, we report micro- and nano-structuration on silicon (Si). The Langmuir-Blodgett (LB) technique is primarily used to realize monolayers of C18 functionalized silica (SiO2) microspheres on a large size area of the substrates. Afterwards, by irradiating the deposited monolayer with single shot UV nanosecond laser pulses in the ablation regime, we demonstrate the formation of dense arrays of craters in silicon substrate. In particular, we describe our works to obtain mono dispersed craters of sub micrometer size using LB technique and taking the fluence and sphere size as variable process parameters. Finite-difference time-domain (FDTD) simulations are presented to estimate the enhancement intensity factor and near-field distribution below the spheres in the experiments.
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.
We have investigated femtosecond-laser-induced microstructures (on the surface and within the bulk), gratings, and craters in four different polymers: polymethyl methacrylate, polydimethylsiloxane, polystyrene, and polyvinyl alcohol. The structures were achieved using a Ti:sapphire laser delivering 100-fs pulses at 800 nm with a repetition rate of 1 kHz and a maximum pulse energy of 1 mJ. Local chemical modifications leading to the formation of optical centers and peroxide radicals were studied using ultraviolet-visible absorption and emission, confocal micro-Raman and electron spin resonance spectroscopic techniques. Potential applications of these structures in microfluidics, waveguides, and memory-based devices are demonstrated.
We have investigated femtosecond laser induced microstructures, gratings, and craters in four
different polymers: poly methyl methacrylate (PMMA), poly dimethyl siloxane (PDMS),
polystyrene (PS) and poly vinyl alcohol (PVA) using Ti:sapphire laser delivering 800 nm, 100
femtosecond (fs) pulses at 1 kHz repetition rate with a maximum pulse energy of 1 mJ. Local
chemical modifications leading to the formation of optical centers and peroxide radicals which
were studied using UV-Visible absorption and emission, confocal micro-Raman and Electron
Spin Resonance (ESR) spectroscopic techniques.
We have fabricated straight line structures and Y-couplers in X-cut lithium niobate crystals using femtosecond laser
pulses. A systematic characterization study was performed initially to determine the effects of pulse energy on feature
size. The optimal parameters were determined from experiments and simulations obtained using a two dimensional split
step beam propagation method. Later the waveguides and couplers were fabricated using these optimized parameters.
We present our results on the physical and optical characterization of these structures.