K. Fedus

Photo-stability of pulsed laser deposited Ge(x)As(y)Se(100-x-y) amorphous thin films.

Quest for photo-stable amorphous thin films in ternary Ge(x)As(y)Se(100-x-y) chalcogenide system is reported. Studied layers were fabricated using pulsed laser deposition technique. Scanning electron microscope with energy dispersive X-ray analyzer, Raman scattering spectroscopy, transmittance measurements, variable angle spectroscopic ellipsometry, and non-linear imaging technique with phase object inside the 4f imaging system were employed to characterize prepared thin films. Their photo-stability/photo-induced phenomena in as-deposited and relaxed states were also investigated, respectively. In linear regime, we found intrinsically photo-stable relaxed layers within Ge(20)As(20)Se(60) composition. This composition presents also the highest optical damage threshold under non-linear optical conditions.

Absolute measurement of the nonlinear refractive indices of reference materials

We report absolute measurements of the nonlinear refractive index on carbon disulfide (CS2) and fused silica. These materials are commonly used as standard references in nonlinear optical experiments. To obtain more accurate values than those usually used, we have combined the z-scan method inside a 4-f imaging system (in order to analyze the spatial distortion of the diffracted pump beam) with the “Kerr shutter” experiment (to evaluate the temporal pulse width durations for three different wavelengths such as 1064, 532, and 355 nm). We obtained surprisingly n2 values one order of magnitude less than the one usually taken into account in the picosecond regime and a more significant dispersion of the nonlinear refraction index. Experimental and simulated Z-scan transmittance profiles as well as acquired autocorrelation functions in the Kerr-gating experiments are presented here in order to validate our measurements.

Photoinduced effects in thin films of Te20As30Se50 glass with nonlinear characterization

We discuss the influence of photoinduced effects (PIEs) on the measurements of nonlinear refractive indices and nonlinear absorption coefficients. A chalcogenide glass film Te20As30Se50 was studied using picosecond laser pulses at 1064 nm. The nonlinear imaging technique with phase object (NIT-PO) and the Z-scan technique were applied and their results are compared. The NIT-PO technique reveals clearly the influence of PIE on the samples’ response, while by using the Z-scan technique we measured the deepness of ablated regions (holes) produced during the measurements.

Nonlinear characterization of GeS2–Sb2S3–CsI glass system

We present the results of Z-scan measurements (1064 nm, 17 ps) of nonlinear refractive indices and nonlinear absorption coefficients for different compositions of chalcogenide glasses in GeS2–Sb2S3–CsI system. We show that the simple well known Boling, Glass, and Owyoung model based on the theory of the semiclassical harmonic oscillator can be a useful tool for theoretical predictions of the nonlinear refractive index in these infrared glasses. A quasi-linear behavior is observed relating the nonlinear index and the linear one. Some of the compositions reveal properties potentially useful for all optical switching applications.

Degenerate multiwave mixing using Z-scan technique

This study deals with a multiwave mixing experiment using Z-scan technique. We show that it is possible to simplify the complex degenerate four-wave mixing(DFWM) experimental setup in order to characterize nonlinear materials. One object composed of three circular apertures is used as an input in a 4 f coherent imaging system. When the nonlinear material is moved around the focus, we observe the variations of the forward fourth wave at the output as well as other diffracted waves. Experimental and simulated images are presented here to validate our approach. We show also that this method increases significantly the sensitivity of the measurement compared to DFWM. We provide a simple quadratic relation that allows the characterization of the cubic optical nonlinearity.

Nonresonant third-order nonlinear properties of NaPO3―WO3―Bi2O3 glasses in the near infrared

n2, was 10 �15 cm 2 / W and the NL absorption coefficient, 2, varied from 0.3 to 0.5 cm/GW for WO3 concentrations varying from 20% to 50%. The experiments in the infrared did not show relevant NL behavior for WO3 concentrations smaller than 50%. In this paper, we report on the third-order nonlinearity of NaPO3 –W O3 –B i2O3 glasses that present large NL response in the near infrared. The presence of Bi2O3 instead of BaF2 in the glass composition contributes for the increase in the NL response because of the larger Bi2O3 polarizability. The samples prepared have good optical quality, they are stable against moisture, and have large optical damage threshold. The experiments performed in the infrared indicate large values of n2 for the different compositions investigated. Two variations in the Z-scan technique at 1064 and 800 nm, with picosecond and femtosecond laser pulses, respectively, were applied for characterization of the samples. From the experiments, we determine n2 10 �15 cm 2 / W, one order of magnitude larger than silica, and negligible NL absorption coefficient. Figures of merit for all-optical switching were determined using the NL parameters measured and the results indicate large potential of NaPO3 –W O3 –B i2O3 glasses for photonic devices in the near infrared.

Sensitivity of the 4f coherent imaging system used in degenerate multiwave mixing experiments

We analyze the influence of different objects on the sensitivity of using a 4f imaging system for nonlinear optical measurements. By defining the diffraction efficiency as the physical quantity to measure, it is possible to perform different measuring methods (Z-scan, eclipsing Z-scan, I-scan, degenerate four-wave mixing) by matching the field stop in the image plane with the object at the entry. One, two, three, and four waves mixing are considered in order to compare their related sensitivities. We provide simple quadratic relations for each object that allow the characterization of the cubic optical nonlinearity. A systematic comparison is done showing that one circular aperture object gives the highest sensitivity. The experimental measurements are performed in order to validate our simulation.

Near-infrared Kerr nonlinearity of Pb(PO3)(2)-WO3 glasses

We report measurements of the nonlinear refractive index, n2, and the nonlinear absorption coefficient, α2, of Pb(PO3)2–WO3 glasses. The measurements were performed using 100 fs (17 ps) laser pulses at 800 nm (1064 nm). Positive values of n2∼10−19 m2/W and negligible α2 were measured. The results show that the nonlinearity is faster than 100 fs and it is observed an increase of n2 with the increasing of the WO3 amount in the samples. The Boling, Glass, and Owyoung model, based on the semiclassical harmonic oscillator model, was used to predict the values of n2, with basis on the values of the linear refractive index of the samples.

Linear optical characterization of transparent thin films by the Z-scan technique

We report experimental characterization of a very small rectangular phase shift (<0.3 rad) obtained from the far-field diffraction patterns using a closed aperture Z-scan technique. The numerical simulations as well as the experimental results reveal a peak-valley configuration in the far-field normalized transmittance, allowing us to determine the sign of the dephasing. The conditions necessary to obtain useful Z-scan traces are discussed. We provide simple linear expressions relating the measured signal to the phase shift. A very good agreement between calculated and experimental Z-scan profiles validates our approach. We show that a very well known nonlinear characterization technique can be extended for linear optical parameter estimation (as refractive index or thickness).

Determination of photo-induced changes in linear optical coefficients by the Z-scan technique

We introduce a Z-scan technique as a tool to characterize small phase shift (<1 rad) and photodarkening, both effects induced inside photosensitive materials by light illumination. Theoretical analysis supported by experiments is presented for permanent refraction and absorption Gaussian profiles. Simple relations are derived in order to estimate the changes in the linear coefficients. Particularly, we investigate quantitatively the photo-induced modifications in the linear optical constants of As2S3 caused by subbandgap irradiation (17 ps, 1064 nm).