Gallium and titanium diffused optical waveguide devices in sapphire

This thesis describes new methods to realise an integrated Ti:Sapphire laser using thermal ionic diffusion. Passive and active waveguides were fabricated by thermal diffusion of gallium and titanium ions in sapphire.Theoretical simulations were established which describe the potential of planar Ti:Sapphire waveguide lasers and intracavity wavelength selection devices. A diffusion study of gallium, titanium and gallium/titanium co-doping is presented; the diffusion coefficient of gallium ions in sapphire was calculated to be 3.3x10-17 m2s-1 at 16000 °C and the diffusion coefficient of titanium ions in sapphire at 16000 °C was found to be 1.7x10-15 m2s-1. Planar Ga:Sapphire passive waveguides were realised by thermal diffusion of gallium ions. The refractive index of sapphire at 800nm is approximately 1.766 and the index change induced by gallium doping was found to be up to 6x10-3 and the mode sizes of the waveguides were as small as 1µm at 488nm. A fabrication procedure based on SU-8 photolithography and ion beam milling was developed for micromachining the surface of sapphire. Using this fabrication technique Ga:Sapphire ridge waveguides were fabricated by diffusion of gallium and exhibited mode sizes as small as 2µm at 633nm. Using the same fabrication technique the realisation of the first Ti-diffused sapphire ridge waveguide lasers is reported. Finally, the fabrication of sapphire optical circuits using titanium and gallium co-doping is described and fluorescence characterisation of these waveguides is given

Resurrecting anti-virtualization and anti-debugging: Unhooking your hooks

Dynamic malware analysis involves the debugging of the associated binary files and the monitoring of changes in sandboxed environments. This allows the investigator to manipulate the code execution path and environment to develop an understanding of the malware’s internal workings, aims and modus operandi. However, the latest state of the art malware may incor- porate anti-virtual environment (VM) and anti-debugging countermeasures (i.e. to determine whether the malware is being executed in a VM or us- ing a debugger prior to payload execution). We argue that for the malware to be effective, it will need to support an array of anti-detection and eva- sion mechanisms. In essence, from the malware’s perspective, it needs to adopt a “defence in depth” paradigm to achieve its underlying business logic functionality. Beyond the malicious uses, software vendors to preserve the intellectual property rights of their products often resort to similar methods to deter competitors from gaining intelligence from the binaries or prevent customers from using their products in unauthorised hardware. In this work, we illustrate how Windows architecture impedes the work of debuggers when they analyse with armoured binaries. The debugger and the malware have the same privileges, so the attacker may manipulate theaddress space that the debugger operates and, e.g. bypass detection. We showcase this by presenting a new framework (ANTI), which automates the procedure of integrating anti-debugging and anti-VM in the binary. Specifi- cally, ANTI introduces an anti-hooking method targeting Windows binaries, where hooks applied by state of the art debuggers are removed and injects its code in other processes. This significantly compounds the challenge of binary analysis. Our extensive evaluation also demonstrates that ANTI successfully circumvents detection from state-of-the-art detection methods. Therefore, ANTI illustrates that current tools for dynamic analysis have serious implementation gaps that allow for binaries to bypass them. More alarmingly, ANTI shows how one can use well-known methods to “resurrect” old attacks

175 GHz, 400-fs-pulse harmonically mode-locked surface emitting semiconductor laser

We report a harmonically mode-locked vertical external cavity surface emitting laser (VECSEL) producing 400 fs pulses at a repetition frequency of 175 GHz with an average output power of 300 mW. Harmonic mode-locking was established using a 300 µm thick intracavity single crystal diamond heat spreader in thermal contact with the front surface of the gain sample using liquid capillary bonding. The repetition frequency was set by the diamond microcavity and stable harmonic mode locking was achieved when the laser cavity length was tuned so that the laser operated on the 117th harmonic of the fundamental cavity. When an etalon placed intracavity next to the gain sample, but not in thermal contact was used pulse groups were observed. These contained 300 fs pulses with a spacing of 5.9 ps. We conclude that to achieve stable harmonic mode locking at repetition frequencies in the 100s of GHz range in a VECSEL there is a threshold pulse energy above which harmonic mode locking is achieved and below which groups of pulses are observed

Simulation of metallic nanostructures for emission of THz radiation using the lateral photo-Dember effect

A 2D simulation for the lateral photo-Dember effect is used to calculate the THz emission of metallic nanostructures due to ultrafast diffusion of carriers in order to realize a series of THz emitters.Comment: Corrected version of a paper given at 2011 36th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz

Unpublished Mediterranean and Black Sea records of marine alien, cryptogenic, and neonative species

To enrich spatio-temporal information on the distribution of alien, cryptogenic, and neonative species in the Mediterranean and the Black Sea, a collective effort by 173 marine scientists was made to provide unpublished records and make them open access to the scientific community. Through this effort, we collected and harmonized a dataset of 12,649 records. It includes 247 taxa, of which 217 are Animalia, 25 Plantae and 5 Chromista, from 23 countries surrounding the Mediterranean and the Black Sea. Chordata was the most abundant taxonomic group, followed by Arthropoda, Mollusca, and Annelida. In terms of species records, Siganus luridus, Siganus rivulatus, Saurida lessepsianus, Pterois miles, Upeneus moluccensis, Charybdis (Archias) longicollis, and Caulerpa cylindracea were the most numerous. The temporal distribution of the records ranges from 1973 to 2022, with 44% of the records in 2020–2021. Lethrinus borbonicus is reported for the first time in the Mediterranean Sea, while Pomatoschistus quagga, Caulerpa cylindracea, Grateloupia turuturu, and Misophria pallida are first records for the Black Sea; Kapraunia schneideri is recorded for the second time in the Mediterranean and for the first time in Israel; Prionospio depauperata and Pseudonereis anomala are reported for the first time from the Sea of Marmara. Many first country records are also included, namely: Amathia verticillata (Montenegro), Ampithoe valida (Italy), Antithamnion amphigeneum (Greece), Clavelina oblonga (Tunisia and Slovenia), Dendostrea cf. folium (Syria), Epinephelus fasciatus (Tunisia), Ganonema farinosum (Montenegro), Macrorhynchia philippina (Tunisia), Marenzelleria neglecta (Romania), Paratapes textilis (Tunisia), and Botrylloides diegensis (Tunisia).peer-reviewe

Complex refractive index determination using planar and converging beam transfer functions

Terahertz time domain spectroscopy can help us to determine the complex refractive index of materials. To achieve this a theoretical model of the spectrometer has to be implemented; a usual method for refractive index determination is to fit a theoretically calculated transfer function to the experimental data. Material parameter extraction models based on transfer functions can be of varying complexity based on the requirements for accuracy and also the difficulty of factoring all experimental parameters. Here, we are going to show how algorithms based on transfer functions with different complexity can be setup. It will be described howa transfer function can be used to extract the refractive index of material and the key stages of the analysis, the fitting algorithm, and the need for phase unwrapping. Transfer functions of an increasing complexity will be shown, with and without the etalon term, using planar or converging beam. © Springer-Verlag Berlin Heidelberg 2013. © Springer-Verlag Berlin Heidelberg 2013

Simulation of THz generation and propagation from photo-Dember emitters

We demonstrate a simulation of lateral photo-Dember terahertz (THz) emitters in two dimensions using the drift diffusion equation coupled to a finite-difference time-domain model with a far-field algorithm that can take into account the angular spectrum of emission and propagation. We show that the dynamics of the system are more dependent on the currents traveling perpendicular to the semiconductor surface, as opposed to just the lateral currents as previously thought. The 2D simulation is needed in order to correctly represent experiments that measure emission out of lateral photo-Dember emitters.</p