Nonlinear Two-Photon Absorption in the Near-Infrared Band for Lead Bromide Perovskite Films Using an F-Scan Nonlinear Spectrometer.

An F-scan nonlinear spectrometer is used to measure the two-photon absorption coefficient for CH3NH3PbBr3 perovskite films from 690 to 995 nm. This spectrometer uses an electrically focused tunable lens and a tunable femtosecond-pulse laser (Mai Tai-HP) with a resolution of 5 nm. Two-band models and saturation irradiance corrections are used to fit the experimental data. The nonlinear absorption in this wavelength range is of the order of cm/MW. We found that the best agreement between the experimental data, the reported values in the literature, and the theoretical model is obtained for an extended two-band model with irradiance saturation correction.

Experimental generation of adjustable partially coherent optical vortices from coherent and incoherent light sources.

Adjustable spatial coherence systems allow the possibility to make different intensity distributions using one source. Most common adjustable sources are based on the Collet-Wolf system. However, it is also possible to adjust the spatial coherence of the illumination field from white light sources by spatially filtering the source mutual intensity spectrum. We implement the Collet-Wolf source and the LED-based system to experimentally contrast a variety of partially coherent optical vortices that can be generated with spatial light modulation. We experimentally study the effects of changing the transverse coherence in partially coherent optical vortices, using a proposed metric of vortex contrast depth that quantifies the change of the vortex hollowness. To expand the analysis, we use a Michelson interferometer to reconstruct the spiral wavefronts using phase shifting. We found that the LED system at lower spatially correlated light produces truncated triangular distributions (a 50 µm pinhole is used), and with higher correlated light, it produces partially coherent optical vortices (a 10 µm pinhole is used). The Collet-Wolf system generates partially coherent optical vortices up to 0.5 mm of focal shift in the diffuser. Our results provide an experimental understanding and instrumental methodology capable of steering the optical transverse coherence, producing adjustable partially coherent optical vortices that can be obtained using incoherent and coherent sources.

Experimental Investigation of the Effect of Adding Nanoparticles to Polymer Flooding in Water-Wet Micromodels.

Recently, the combination of conventional chemical methods for enhanced oil recovery (EOR) and nanotechnology has received lots of attention. This experimental study explores the dynamic changes in the oil configuration due to the addition of nanoparticles (NPs) to biopolymer flooding. The tests were performed in water-wet micromodels using Xanthan Gum and Scleroglucan, and silica-based NPs in a secondary mode. The microfluidic setup was integrated with a microscope to capture the micro-scale fluid configurations. The change in saturation, connectivity, and cluster size distributions of the non-wetting phase was evaluated by means of image analysis. The biopolymer content did not affect the ability of the NPs to reduce the interfacial tension. The experiments showed that the reference nanofluid (NF) flood led to the highest ultimate oil recovery, compared to the Xanthan Gum, Scleroglucan and brine flooding at the same capillary number. In the cases of adding NPs to the biopolymer solutions, NPs-assisted Xanthan flooding achieved the highest ultimate oil recovery. This behavior was also evident at a higher capillary number. The overall finding suggests a more homogenous dispersion of the NPs in the solution and a reduction in the polymer adsorption in the Xanthan Gum/NPs solution, which explains the improvement in the sweep efficiency and recovery factor.

Master key generation to avoid the use of an external reference wave in an experimental JTC encrypting architecture.

In experimental optodigital encrypting architectures, the use of a reference wave is essential. In this contribution, we present an experimental alternative to avoid the reference wave during the encrypting procedure in a joint transform correlator architecture by introducing the concept of a master key. Besides, the master key represents an additional security element for the entire protocol. In our method, the master key is holographically processed and used during the encryption process with the encrypting key. We give the mathematical description for the process in case of a single input object and then we extend it to multiple input objects. We present the experimental demonstration of the proposed method including two examples where this technique is successfully applied for several input objects.

Experimental multiplexing of encrypted movies using a JTC architecture.

We present the first experimental technique to encrypt a movie under a joint transform correlator architecture. We also extend the method to multiplex several movies in a single package. We use a Mach-Zehnder interferometer to encrypt experimentally each movie. One arm of the interferometer is the joint transform correlator and the other arm is the reference wave. We include the complete description of the procedure along with experimental results supporting the proposal.

Noise-free recovery of optodigital encrypted and multiplexed images.

We present a method that allows storing multiple encrypted data using digital holography and a joint transform correlator architecture with a controllable angle reference wave. In this method, the information is multiplexed by using a key and a different reference wave angle for each object. In the recovering process, the use of different reference wave angles prevents noise produced by the nonrecovered objects from being superimposed on the recovered object; moreover, the position of the recovered object in the exit plane can be fully controlled. We present the theoretical analysis and the experimental results that show the potential and applicability of the method.