Holographic techniques are powerful tools to study photosensitive materials due to the high sensitivity of diffraction measurement and the ability to detect dynamic gratings. The self diffraction technique consists in to project an interference fringe pattern into the photosensitive material and to measure, in real time, the self-diffraction of the interfering beams, at the grating generated in the photosensitive material. Besides the higher sensitivity, such measurement allows to measure simultaneously and separately the phase and the amplitude grating contributions, as well as thin or thick gratings. In order to demonstrate potentiality of this technique we measured the kinetic constant of the photo-reaction in positive photoresists (AZ types) and negative SU-8 photoresist, as well as the maximum values of the refractive index and of the absorption coefficient modulations induced in these materials at different wavelengths of exposure. The same measurements were performed in SB based chalcogenide glasses in order to evaluate the potential of such materials to be used as optical data storage devices.
In this work, we designed and recorded two-dimensional Hexagonal Photonic Crystals (2D-HPC) layers, with a linear waveguide, in erbium doped GeO<sub>2</sub>-Bi<sub>2</sub>O<sub>3</sub>-PbO-TiO<sub>2</sub> glassy films, by combining the techniques of holographic recording and femtosecond (fs) laser micromachining. The 2D-HPC is recorded holographically in a photoresist film coated on a glass substrate by exposing the sample to the same interference pattern twice and rotating the sample of 60° between the exposures. After the development a two dimensional hexagonal array of photoresist columns remain on the glass substrate. The recording of the waveguide is made by a fs laser micromachining system focused at sample surface. The laser spot produces the ablation of the photoresist columns generating a defect line in the periodic hexagonal array. After the recording of the photoresist template, the erbium doped GeO<sub>2</sub>-Bi<sub>2</sub>O<sub>3</sub>-PbO-TiO<sub>2</sub> film is evaporated on the photoresist and finally the photoresist template is removed using acetone. The design of the geometrical parameters of the 2D-HPC is performed by calculation of the dispersion mode curves of the photonic crystal using a 2D finite element method. The proper geometrical parameters depend on both the refractive index of the glass film and thickness. Such parameters as well as the period of the 2D-HPC have been defined in order to obtain a photonic band gap in the region of erbium luminescence band. In such condition the erbium luminescence will propagate only through the waveguide.
In this work we demonstrate the use of holographic lithography for generation of large area plasmonic periodic
structures. Submicrometric array of holes, with different periods and thickness, were recorded in gold films, in areas of
about 1 cm<sup>2</sup>, with homogeneity similar to that of samples recorded by Focused Ion Beam. In order to check the
plasmonic properties, we measured the transmission spectra of the samples. The spectra exhibit the typical surface
plasmon resonances (SPR) in the infrared whose position and width present the expected behavior with the period of the
array and film thickness. The shift of the peak position with the permittivity of the surrounding medium demonstrates the
feasebility of the sample as large area sensors.
In this work we studied the changes of the optical constants of films in the binary system Sb<sub>2</sub>O<sub>3</sub>-Sb<sub>2</sub>S<sub>3</sub> induced by light in
the VIS-UV. The measurements were performed before and after homogeneous irradiation of the films to a Hg lamp and
in real time during the holographic exposure of the samples (at 458nm). Changes of the absorption coefficient (amplitude
grating) and refractive index (phase grating) were measured simultaneously using the self-diffraction using the
holographic setup. Besides the films presented a strong photodarkening effect under homogeneous irradiation, the
samples holographically exposed presented only refractive index modulations. None amplitude modulation was
measured in real time for spatial frequencies of about 1000 l/mm.
Different technologies can be used for fabrication of photonic crystals such as: self-assembly of colloidal particles, ebeam
lithography (EB), interference lithography (IL) and focused ion beam (FIB). Among them, the holographic
lithography (HL) is the only technique that is able to fabricate both two-dimensional and three-dimensional photonic
crystals, as well as plasmonic structures, in large areas. In this paper we demonstrate the use of the multi-exposure of
two-beam interference patterns, with rotation of the sample around different axis, for fabrication of large areas 2D and 3
D photonic crystals and plasmonic structures. Using this technique, we achieved aspect ratios of about 4 in 2D
photoresist templates recorded in 1 cm<sup>2</sup> glass substrates. In order to generate the 2D photonic band gap layers and
plasmonic structures, we combine the use the high aspect ratio photoresist templates with shadow evaporation of
appropriated materials, with a further lift-off of the photoresist. The optical properties of the recorded structures, both
photonic and plasmonic, were measured to demonstrate the applicability of the technique.
Sieves are membranes with a regular array of uniform pores that present low flow resistance. Because of such
characteristics they are promising devices for filtration, separation of particles by size and drug delivery control. If the
pore dimensions reach the scale of nanometers, new and exciting biological applications may be developed. We propose
and demonstrated a technique for fabrication of polymeric sieves using only soft lithography that allows the mass
production of sieves with pores in the scale of hundred of nanometers. The technique associates UV interference
lithography, conventional optical lithography and molding. The process starts with the UV interference lithography in a
thin SU-8 photoresist film, in order to record the small pores. After development, a thick SU-8 layer is coated, on the
previously recorded sample, in order to pattern a hexagonal sustaining structure. The structures recorded in SU-8 are
used to create a negative mold in PDMS (Polydimethylsiloxane) that is used for casting the sieve in PLLA (poly-Llactide).
Self-sustaining Nickel membranes with periodic and regular distribution of pores, in the scale of hundred of nanometers, were produced by interference lithography and electroplating. The process consists in the recording of submicrometric 2D periodic photoresist columns, on a metal-coated glass substrate, using the double exposure of an interference fringe pattern. As the photoresist is a good electrical isolator, when the sample is immersed in a Ni electroplating bath, the array of photoresist columns impedes the Nickel deposition in the patterned areas. A nickel film is then growth among the photoresist columns with a thickness up to 80 % of the height of the columns. In order to release the submicrometric
membrane from the substrate, a thick hexagonal Nickel sustaining structure is electroformed, using conventional photolithography. The dimensions of the sustaining structure can be adapted in order to fulfill the pressure requirements of the filtration system. The good uniformity of the pore sizes as well as the smooth of the surface make such devices very interesting for separation of particles by size in filtration systems.
In this paper we describe the replication processes of DOE carried out at the Diffractive Optics Laboratory/UNICAMP for replicating DOE. In particular we present the results obtained in the replication by injection molding of microlens array, diffraction gratings and polarizing elements. The measurements of the geometric dimensions of the DOE masters, the nickel shims and the replicated structures were accomplished by perfilometry, AFM and SEM microscopy. The optical properties of both the DOE masters and their replicas were evaluated by measuring of the diffraction efficiency as a function of the incident wavelength, for orthogonal polarizations.
Two dimensional photonic crystals slabs can be recorded using a double exposure of a photoresist film to an interference fringe pattern. In order to present an expressive PBG (photonic band gap) for a desired region of the electromagnetic spectrum, the geometry of the 2 dimensional structures must be appropriately defined. Besides the geometric requirements, the material itself, in which the structures are recorded, must be transparent and present high refractive index in electromagnetic region of the PBG. In this paper we design and fabricate two dimensional (PC) Photonic Crystals) in dielectric films on glass substrates. The use of optical materials instead of semiconductors allows the devleopment of processes able to produce P.C. for the visible part of the spectrum.
In this paper we proposed and demonstrated the association of holographic lithography with electroforming to produce submicrometric metallic structures. To demonstrate the potential of the technique, different types of submicrometric metallic structures were generated: periodic lines, nano-tunnels and arrays of holes. Such structures can met different applications from optics to micromechanical systems.
In this paper it is presented recent developments in the heterodyne detection holographic techniques for studding photosensitive materials. The actual state of the technique allows simultaneous and independent measurement of the refractive index and of the absorption coefficient changes in photosensitive materials and their use to self-stabilize the fringe pattern. The modeling of the measured signal together with the fringe stabilization allow the long term-fitting of the optical properties and the study the photosensitive materials close to the saturation.
The lithography of gratings or structures using photoresist holographic masks is very critical, in particular when high selectivity etching processes were employed. In this paper we study the effect of the mask profile and of the phase perturbations during the holographic exposure in the noise of the photoresist masks. It is shown that the use of appropriate conditions of development and exposure may reduce significantly this noise allowing the recording of high aspect ratio structures and the use of selective deposition techniques.
New diffractive optical elements were performed by holographic exposition of photoresist masks and reactive ion etching of the substrates. In particular we report the project and fabrication of a diffractive element which splits the incident unpolarized light its two orthogonal polarizations by reflection.
A theoretical model is developed to compute the resulting profile of structures holographically recorded in photoresists. The model takes into account the effects of exposure, photosensitization and isotropy of wet development. The effects of isotropy of wet development, non-linearity of the photoresist response curve, background-light, and the stationary waves produced by reflection at the film-substrate interface are analyzed using the model and the results are experimentally confirmed.
Photoelectrochemical (PEC) etching of n-InP is studied as a method to engrave relief microstructures. Experiments of PEC were performed with holographic exposures ((lambda) equals 0.4579 micrometers ) and homogeneous white light on n-InP. The triangular profile characteristic of holographic patterns recorded parallel to the <011> direction appeared even when the sample was etched using homogeneous white light. In this case deep random microstructures were obtained that present interesting anti-reflecting properties that may be useful in solar cells applications.