Stabilization of an AM mode-locked tea CO2 laser

An increased shot-to-shot reproducibility has been obtained by injection of radiation from a cw CO2 laser in an amplitude mode-locked TEA CO2 laser without additional pulse broadening. Stable pulses variable from 900 ps up to 4 ns have been generated with this new technique

Increased reliability of passive mode-locking a multi-atmosphere TE CO2 laser by injection mode-locking

By injection of manosecond pulses from an AM mode-locked TEA CO2 laser in a passive mode-locked multi-atmosphere TE CO2 laser the shot-to-shot reproducibility of the generated subnanosecond pulses was increased to almost 100%

Line broadening in an AM mode-locked TEA-CO2 laser

By means of injection mode-locking, we were able to measure the bandwidth limited pulse duration of an AM mode-locked TEA-CO2 laser for different laser-gas mixtures. From these measurements we confirm the theoretical relation between bandwidth and pulse duration. The bandwidth under laser discharge conditions is similar to that of the neutral gas

Pulse forming in an AM mode-locking hybrid TEA-CO2 laser

We performed an experimental study on the pulse forming mechanism in an AM mode-locked hybrid TEA-CO2 laser by means of “injection mode-locking”. The results show that bandwidth limited pulses will only be reached within a small - critical - range of parameters. Furthermore, under some stringent conditions, the pulse-widths obtained become comparable to the non-hybrid case. We demonstrate also that the relation between the pulse-width and the modulation-depth is not different from a non-hybrid AM mode-locked TEA-CO2 laser

Transport in graphene antidot barriers and tunneling devices

Periodic arrays of antidots, i.e. nanoscale perforations, in graphene enable tight confinement of carriers and efficient transport barriers. Such barriers evade the Klein tunneling mechanism by being of the mass rather than electrostatic type. While all graphene antidot lattices (GALs) may support directional barriers, we show, however, that a full transport gap exists only for certain orientations of the GAL. Moreover, we assess the applicability of gapped graphene and the Dirac continuum approach as simplified models of various antidot structures showing that, in particular, the former is an excellent approximation for transport in GALs supporting a bulk band gap. Finally, the transport properties of a GAL based resonant tunneling diode is analyzed indicating that such advanced graphene based devices may, indeed, be realized using GAL structures.Comment: 12 pages, 9 figures, accepted for publication on Journal of Applied Physic

Tight-binding study of the magneto-optical properties of gapped graphene

We study the optical properties of gapped graphene in presence of a magnetic field. We consider a model based on the Dirac equation, with a gap introduced via a mass term, for which analytical expressions for the diagonal and Hall optical conductivities can be derived. We discuss the effect of the mass term on electron-hole symmetry and $\pi$-$\pi^*$ symmetry and its implications for the optical Hall conductivity. We compare these results with those obtained using a tight-binding model, in which the mass is modeled via a staggered potential and a magnetic field is included via a Peierls substitution. Considering antidot lattices as the source of the mass term, we focus on the limit where the mass term dominates the cyclotron energy. We find that a large gap quenches the effect of the magnetic field. The role of overlap between neighboring $\pi$ orbitals is investigated, and we find that the overlap has pronounced consequences for the optical Hall conductivity that are missed in the Dirac model.Comment: 10 pages, 9 figures, submitted for Physical Review

The influence of charge-mode operation of a XeCl laser on the beam profile

The shape of the beam profile of a discharge excited XeCl excimer laser using a spiker-sustainer electrical circuit has been varied from a `bell¿-, through a `top-hat¿-, to a `camel-back¿-profile by varying the delay between the spiker pulse and the main-current with the circuit operating in the charge-mode. Fine-tuning of the beam profile can be done by varying the charging voltage of the main pulse forming network or the temperature of a gas purifier regulating the Xe and HCl partial pressures

An independently adjustable multiline AM mode-locked TEA CO2laser

A new method is described for constructing an AM mode-locked, multiline TEA CO2laser oscillator generating nanosecond pulses. The multiline behavior is achieved by spatial separation of the rotational transitions at the amplifying medium. The setup generates 1.15 ns pulses with an energy of 3.7 mJ per pulse and containing simultaneously six rotational transitions in the 10.6 µmP-branch

Beam divergence studies on a hard edge unstable resonators for a long pulse XeCl excimer laser

The focusability of a long pulse XeCl excimer laser has been improved using confocal positive branch unstable resonators where the outcoupling is done through the convex mirror. A nearly diffraction limited output beam is obtained from hard edge unstable resonators. An improvement of the far field energy distribution is achieved with partial reflecting hard edge outcoupling mirrors. The phase delay between the central part of the beam and the beam edge caused by these partial reflecting mirrors can be reduced by using phase unifying mirrors. Using unstable resonators a brightness of 1.4 × 1015 W/cm2 sr has been obtained from a long pulse XeCl excimer lase