The transfer matrix of a dielectric slab under propagation of a Gaussian beam was formulated. The derived matrix was applied for a one-dimensional photonic crystal (1DPC) structure and the transmittance spectrum and photonic bandgap (PBG) properties were investigated. An r-dependent (r is the radial coordinate of the Gaussian beam) PBG was obtained. With the increase of r, a redshift and a decrease in the PBG are observed. Higher PBGs experience more shift. Also properties of the photonic crystal (PC) structure with defect layer were investigated and displacement to red and decrease of the defect mode peak height, with an increase of r, were observed. The extra optical path that the outer rays travel due to the oblique propagation compared to the central ray in a Gaussian beam is responsible for these effects. For long Rayleigh ranges our results for the Gaussian beam were the same as that for plane wave.
A new field in laser processing is opened by a laser-induced modification of the optical properties, i.e. the refractive index, absorption- and scattering-coefficient, inside transparent materials, preferentially optical glasses. Ultra short laser pulses are capable of inducing these modifications without cracking or even melting the glass matrix. The femtosecond and in some cases even picosecond laser technology allows to control and modify the optical properties in the bulk on a sub-µm scale. This is referred to as nik-engineering
TM, relating the experimental technique to changes of
the complex refractive index (n + ik). Three dimensional patterns of the (n + ik) modifications can be achieved in the subsurface region on a microscopic scale. The technical potential for optical applications is challenging and on the verge to be exploited. New results on nik-engineering using ultra-short laser pulses at a wavelength of 800 nm was investigated for special glasses with semi-conductive nano-particles, i.e. photo-chromic and GG/RG filter glasses. This paper discusses the laser-induced optical modification inside these glasses for different laser fluence and shot numbers,
addressing also the possible technological relevance of these effects in respect to decorative work, micro-tagging, and other functional structures.
A theoretical model for laser ablation of polymers is developed. The model includes the description of radiation transport processes for the two-photon stepwise absorption of chromophores. This processes results in a nonlinear loss for the laser fluence, which can be expressed in term of the effective absorption coefficient αeff. The behavior of αeff as a function of incident fluence, applied wavelength, linear, excited state and plume absorption cross sections will be analyzed. This model accounts for a wide variety of observations such as fluence thresholds, wavelength and fluence dependent etch rates. An expression for the etch depth as a function of incident fluence is derived. It will be shown that the theoretical analysis describes accurately the trend of the noval photopolymers ablation results, which are recently reported in literature.