Ultraviolet Optical Pulse Research Articles

Generation of a femtosecond vacuum ultraviolet optical pulse by four-wave Raman mixing

Generation of a femtosecond vacuum ultraviolet optical pulse by four-wave Raman mixing

Spatial Mapping of Pristine and Irradiated AlGaN/GaN HEMTs With UV Single-Photon Absorption Single-Event Transient Technique

Carrier injection by single-photon absorption using ultraviolet optical pulses is used to investigate single-event transients in pristine and proton-irradiated AlGaN/GaN HEMTs. High-precision spatial mapping of defects and traps in AlGaN/GaN HEMT devices identify regions of enhanced SET signals, or “hot spots” that are ascribed to the presence of lattice defects that modify the electric field in the structure. The resulting transient shape and amplitude depend strongly on the specific location of the injected carriers, and vary with changes in gate and drain bias. Proton irradiation significantly alters transient signal shapes, increases the integrated collected charge, and increases density of defects and traps.

Optically-Triggered Nanoscale Memory Effect in a Hybrid Plasmonic-Phase Changing Nanostructure

Nanoscale devices, such as all-optical modulators and electro-optical transducers, can be implemented in heterostructures that integrate plasmonic nanostructures with functional active materials. Here we demonstrate all-optical control of a nanoscale memory effect in such a heterostructure by coupling the localized surface plasmon resonance (LSPR) of gold nanodisk arrays to a phase-changing material (PCM), vanadium dioxide (VO2). By latching the VO2 in a distinct correlated metallic state during the insulator-to-metal transition (IMT), while concurrently exciting the hybrid nanostructure with one or more ultraviolet optical pulses, the entire phase space of this correlated state can be accessed optically to modulate the plasmon response. We find that the LSPR modulation depends strongly but linearly on the initial latched state, suggesting that the memory effect encoded in the plasmon resonance wavelength is linked to the strongly correlated electron states of the VO2. The continuous, linear variation of ...

Toward structural femtosecond chemical dynamics: imaging chemistry in space and time.

We aim to observe a chemical reaction in real time using gas-phase X-ray diffraction. In our initial experiment at the Linac Coherent Light Source (LCLS), we investigated the model system 1,3-cyclohexadiene (CHD) at very low vapor pressures. This reaction serves as a benchmark for numerous transformations in organic synthesis and natural product biology. Excitation of CHD by an ultraviolet optical pulse initiates an electrocyclic reaction that transforms the closed ring system into the open-chain structure of 1,3,5-hexatriene. We describe technical points of the experimental method and present first results. We also outline an approach to analyze the data involving nonlinear least-square optimization routines that match the experimental observations with predicted diffraction patterns calculated from trajectories for nonadiabatic vibronic wave packets.

Single-Event Upsets in Substrate-Etched CMOS SOI SRAMs Using Ultraviolet Optical Pulses With Sub-Micrometer Spot Size

Ultraviolet optical pulses with a full-width-at-half-maximum diameter focused spot size of 0.32 μm are generated, characterized, and used to produce SEUs in a 90 nm CMOS/SOI SRAM. The results provide unequivocal experimental evidence for cell-to-cell variations in SEU sensitivity that can be identified with process variations at the individual transistor level.

Photochemical Reaction Pathways of Carbon Tetrabromide in Solution Probed by Picosecond X-ray Diffraction

We report a liquid-phase time-resolved X-ray diffraction study that resolves the molecular structures of the short-lived intermediates formed in the photodissociation of tetrabromomethane in methanol. Time-resolved X-ray diffraction can detect all chemical species simultaneously, and the diffraction signal from each chemical species can be quantitatively calculated from molecular structures and compared with experimental data with high accuracy and precision. The photochemistry of carbon tetrahalides has long been explored to describe their reactions in the natural environment due to its relevance to ozone depletion. Excited with an ultraviolet optical pulse, the complicated photodissociation dynamics of CBr4 was followed in a wide temporal range from picoseconds up to microseconds and associated rate coefficients were determined by analyzing time-resolved diffraction patterns accumulated from 100 ps X-ray pulses. The homolytic cleavage of one C-Br bond in the parent CBr4 molecule yields the CBr3 and Br radicals, which escape from the solvent cage and combine nongeminately to form C2Br6 and Br2, respectively. C2Br6 eventually decays to give C2Br4 and Br2 as final stable products. Our diffraction data at the current signal-to-noise ratio could not provide any evidence for the geminate recombination of the CBr3 and Br radicals to form the Br2CBr-Br isomer or the solvated ion pair, implying that their formation is a minor channel compared with those observed clearly by time-resolved diffraction in this work.

Ultraviolet picosecond optical pulse generation from a mode-locked InGaN laser diode

Ultraviolet optical pulses were generated by actively mode locking an external cavity InGaN laser at a wavelength of 409 nm with a temporal pulse duration of 30 ps. The average power was 2 mW and the time–bandwidth product was 1.2. Dynamic detuning plays a major role in pulse development.

Evidence of exciton recombination at very high temperature in InGaN

Time-resolved electroluminescence measurements are carried out on the blue light emitting diodes with InGaN active layer at temperatures from 30 to 530 K. The decay mechanisms of the ultraviolet optical pulses corresponding to the band-to-band recombinations are investigated. The exciton-related recombination is found mainly responsible for this band-edge radiative recombination from 250 to 425 K. A thermal equilibrium model, in which the exciton dissociation process is taken into account, is used to fit the experimental results. The fitted exciton binding energy is about 48.3 meV. This high exciton binding energy is attributed to the indium-related localization effect in InGaN. Moreover, it is also found that the nonradiative lifetimes in these samples are quite long. This is ascribed to the suppression of the nonradiative recombination centers because of the incorporation of indium in GaN material.