Theoretical high-efficiency extraction study of a short-pulseelectron-beam-pumped ArF laser amplifier with atmospheric pressureAr-rich mixtures

The single-pass (50 cm) amplifier performance of an atmospheric-pressure ArF laser pumped by a 65-ns full-width-at-half-maximum short-pulse electron beam was investigated theoretically for a wide range of excitation rates (0.1-2.0 MW/cm³ ). Atmospheric mixtures of Ne, Ar, and F₂ (three mixtures of Ar=40%, 70%, and Ne-free) were studied. A kinetic numerical model of the ArF amplifier with a Ne buffer system was constructed. A one-dimensional propagation treatment considered the gain depletion and saturation absorption spatially and temporally along the optical axis. In this model the rate constants for electron quenching of ArF* of 1.6×10^-7, 1.9×10^-7, and 2.4×10 ^-7 cm³/s were used for Ar concentration of 40, 70 percent, and Ar/F₂ mixture, respectively     

F2 laser deposition of CdTe microcrystallites-dopedfluoropolymer thin films

Crystalline thin films of polytetrafluoroethylene (PTFE) were deposited by F₂ laser (157 nm) ablation in 200 mTorr Ar gas atmosphere. Combining this PTFE thin-film process with CdTe microcrystallites synthesis in sizes of 3-7 nm via KrF laser (248 nm) ablation, CdTe microcrystallites-doped PTFE thin films were fabricated. The X-ray photoemission spectra show that the main architecture of PTFE and CdTe are maintained in the doped films. CdTe microcrystallites doped in PTFE matrix show an absorption edge shift toward higher energy and a third-order optical nonlinearity, which are induced by the quantum size effect     

Wide-range all-optical wavelength conversion usingdual-wavelength-pumped fiber Raman converter

A wavelength conversion scheme based on a fiber Raman converter is proposed, in which an externally injected high power pump laser and the associated Stokes laser are used to assist the Raman conversion process of signal light coded with optical information. Because the Raman gain spectrum in fibers is extremely broad, a wavelength conversion device with wide-range tunability is feasible. We numerically demonstrate that wavelength conversion from 1.31 to 1.42 μm can be realized using a fiber Raman converter at up to 10 Gb/s with an efficiency of 18%. It is also demonstrated that wide range conversion from 1.31 to 1.55 μm for optical fiber communication is feasible at up to 5 Gb/s when the fiber Raman converters are cascaded twice     

Characteristics of transients among periodic attractors controlledby high-frequency injection in a chaotic laser diode

We numerically studied statistics of the transient response time when switching between periodic attractors obtained through chaos control with a high-frequency injection method in a laser diode that is subject to optical feedback. Each transient response time significantly depends on its position in the starting attractor, whereas the statistical distributions of the response times for many transients are determined almost entirely by the final attractor. The average transient response time is 40 times larger than the round time in the controlled periodic attractors. The transient response time is also strongly affected by the external cavity length. The shortest average transient response time is obtained at a minimum external cavity length and a zero phase difference between the laser field and the feedback light field     

Theoretical analysis of electron-beam-excited KrF laser performance: New F2concentration optimization

For an electron-beam-excited KrF laser, we analyzed theoretically the dependence of the performance characteristics on the excitation rate and initial F2concentration. According to the analysis of KrF* formation processes, KrF* relaxation processes, 248 nm absorption processes, and their individual efficiencies, a novel optimization method for initial F2concentrations is necessary instead of a conventional method of a "constant" F2burn-up rate. Then, we determined optimum F2concentration as a function of the excitation rate for excitation pulses of 20-500 ns FWHM. Finally, we obtained the scaling law for the intrinsic KrF laser efficiency.     

Theoretical simulation of electron-beam-excited xenon-chloride (XeCl) lasers

By developing a comprehensive computer code fore-beam excited XeCl lasers, we studied mainly the effect of Ar and Ne diluents on the performance characteristics of XeCl lasers. According to the analysis of the XeCl* formation process, the XeCl* relaxation process, and the 308 nm absorption process, it is found that the XeCl* formation efficiency is determined mainly by the rate of the charge transfer process (from Ar+ and Ne+ diluent ions to Xe+); in other words, by the difference between ionic potentials of Xe and the diluent gas used. The extraction efficiency is found to be decided mainly by the quenching rate of a three-body reaction for a short-pulse (55 ns) and a high-excitation-rate (∼ 3 MW/cm³) pumping, and by the absorption process for a long-pulse (500 ns) and a low-excitation-rate (∼ 0.2 MW/cm³) pumping. However, note that no appreciable difference in the intrinsic efficiency is found between the Ar/Xe/HCl and Ne/Xe/HCl mixtures. We also analyzed the dependence of the intrinsic XeCl laser efficiency on the pumping pulse width and excitation rate for Ar/Xe/HCl and Ne/Xe/HCl mixtures. As a result, the same intrinsic efficiencies are obtainable for both Ar- and Ne-based mixtures although the optimum operating conditions are slightly different. The maximum intrinsic efficiency of 5 percent is obtainable both for the Ar/Xe/HCl mixture at 3 atm and with 1.5 MW/cm³, 200 ns (FWHM) pumping and for the Ne/Xe/HCl mixture at 4 atm and with 2 MW/cm³, 200 ns (FWHM) pumping.     

Subpicosecond pulse compression in the VUV region by induced-phasemodulation in Xe

The feasibility of subpicosecond pulse compression in the VUV region using the induced phase modulation in Xe is theoretically studied by numerically solving equations for the amplitude and phase of a weak VUV signal pulse in the presence of an intense pump pulse at the visible wavelength. Substantial pulse compression can be realized with compact pulse compressors when the pump pulse width is decreased. When a 9.6 ps pump pulse at 403 nm with the peak intensity of 1 GW/cm² is assumed, the signal pulse at 157 nm is compressed from 12 ps to 260 fs by the pulse compressor, with a grating-mirror separation of <2.5 m. Influences on the pulse compression of the timing between two incident pulses and the dynamic change in nonlinear susceptibility are also described     

Templating and Replication of Spiral Photonic Crystals for Silicon Photonics

This paper describes femtosecond laser lithography of 3-D photonic crystal templates in commercial photoresist SU-8 and replication of these templates with silicon. Using this approach, silicon-based photonic crystals having 3-D square spiral architecture and exhibiting photonic stop gaps near the 2.5- mum wavelength were fabricated. Possibilities to use a multiple-beam interference technique for two-photon absorption templating of photonic crystals are explored.     

Intracavity second-harmonic generation at 320 nm of an actively Q-switched Pr:LiYF4 laser

We demonstrate pulse laser operation of a Pr:LiYF(4) laser pumped by InGaN laser diodes (444 nm) using an acousto-optic modulator. We obtained a maximum laser peak power of 167 W (4 μJ/pulse) with a pulse width of 24 ns at an 11 kHz repetition rate for a 63 nm wavelength. Employing an 8 mm long lithium triborate nonlinear crystal in the laser cavity, we obtained a maximum peak power of 55 W (2.7 μJ/pulse) at 320 nm, which corresponds to a conversion efficiency of 69% with respect to the fundamental laser energy. The UV laser pulse width was 36 ns.