F.A. van Goor

Effect of frequency variation on electromagnetic pulse interaction with charges and plasma

The effect of frequency variation (chirp) in an electromagnetic (EM) pulse on the pulse interaction with a charged particle and plasma is studied. Various types of chirp and pulse envelopes are considered. In vacuum, a charged particle receives a kick in the polarization direction after interaction with a chirped EM pulse. Interaction of a one-dimensional chirped pulse with uniform plasma is considered. We found that the amplitude of the wake wave generated in plasma by an EM pulse can be significantly higher when the pulse is chirped.

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 laser

Improved x‐ray switched XeCl laser

The performance of a discharge excited XeCl laser has been studied using three different excitation circuits; spiker‐sustainer excitation with a ferrite saturable inductor as the main switch; x‐ray switching with a fast rise time x‐ray preionization pulse, and x‐ray triggering with a saturable inductor and a peaking capacitor added to the circuit. This circuit can improve the performance of the x‐ray switched XeCl laser considerably.

A new mode to excite a gas-discharge XeCl laser

The charge mode is a new mode to excite a discharge XeCl laser based on the dynamics of a spiker-sustainer circuit with a magnetic pulse compressor. The breakdown voltage is higher than in any other mode, due to a very fast rise time. The higher breakdown voltage provides a wider discharge and we found that more energy can be deposited before discharge instabilities terminate the optical output.

Coherent and incoherent radiation from a channel-guided laser wakefield accelerator

Coherent and incoherent electromagnetic radiation emitted from a channel-guided laser wakefield accelerator (LWFA) is calculated based on the Lienard–Wiechert potentials. It is found that at wavelengths longer than the bunch length, the radiation is coherent. The coherent radiation, which typically lies in the infrared range, shows features that reveal details of the acceleration process and properties of the electron bunch, such as its duration, charge, energy, and offset with respect to the wakefield axis. It is found that the LWFA emits energy predominantly in the coherent range of frequencies. The incoherent range of the spectrum, which extends to the x-ray frequency range, consists of rather broad peaks caused by the acceleration. The radiated energy, power and the pulse duration are estimated.

Spectral purification and infrared light recycling in extreme ultraviolet lithography sources

We present the design of a novel collector mirror for laser produced plasma (LPP) light sources to be used in extreme ultraviolet (EUV) lithography. The design prevents undesired infrared (IR) drive laser light, reflected from the plasma, from reaching the exit of the light source. This results in a strong purification of the EUV light, while the reflected IR light becomes refocused into the plasma for enhancing the IR-to-EUV conversion. The dual advantage of EUV purification and conversion enhancement is achieved by incorporating an IR Fresnel zone plate pattern into the EUV reflective multilayer coating of the collector mirror. Calculations using Fresnel-Kirchhoffs diffraction theory for a typical collector design show that the IR light at the EUV exit is suppressed by four orders of magnitude. Simultaneously, 37% of the reflected IR light is refocused back the plasma.

Generating ultrarelativistic attosecond electron bunches with laser wakefield accelerators

Femtosecond electron bunches with ultrarelativistic energies were recently generated by laser wakefield accelerators. Here we predict that laser wakefield acceleration can generate even attosecond bunches, due to a strong chirp of the betatron frequency. We show how the bunch duration scales with the acceleration parameters and that, after acceleration, the bunches can propagate over many tens of centimeters without a significant increase in duration.

Design and simulation of laser wakefield acceleration with external electron bunch injection in front of the laser pulse

In this article we present a theoretical investigation on an experimental design of a laser wakefield accelerator in which electron bunches from a photocathode radio frequency linac are injected into a capillary discharge plasma channel just in front of a few tens of terawatt drive laser pulse. The electron bunch, with a kinetic energy of 2.9 MeV and an energy chirp imposed by the linac, is magnetically compressed by a factor of 8 to a duration of 250 fs, and is magnetically focused into the plasma channel where it matches the spot size of the drive laser ([approximate]30 µm). The dynamics of the bunch, starting from the photocathode, through the linac, along the beam transportation line, through the magnetic compressor, and its focusing into the plasma channel are comprehensively simulated with the general particle tracer code. Further, we use our three-dimensional numerical codes to calculate the laser wakefield and to determine and optimize the trapping and acceleration of the injected bunch in the wakefield. We show that, injecting a 5 pC electron bunch of 250 fs duration, the experiment should deliver an electron bunch of approximately 744 MeV energy, with 1.1% relative energy spread, and with an extremely short duration (6 fs), after acceleration in a 5.4 cm long plasma channel

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.

Electron bunch injection at an angle into a laser wakefield

External injection of electron bunches longer than the plasma wavelength in a laser wakefield accelerator can lead to the generation of femtosecond ultrarelativistic bunches with a couple of percent energy spread. Extensive study has been done on external electron bunch (e.g. one generated by a photo-cathode rf linac) injection in a laser wakefield for different configurations. In this paper we investigate a new way of external injection where the electron bunch is injected at a small angle into the wakefield. This way one can avoid the ponderomotive scattering as well as the vacuum-plasma transition region, which tend to destroy the injected bunch. In our simulations, the effect of the laser pulse dynamics is also taken into account. It is shown that injection at an angle can provide compressed and accelerated electron bunches with less than 2% energy spread. Another advantage of this scheme is that it has less stringent requirements in terms of the size of the injected bunch and there is the potential to trap more charge.