Wolfgang Ziegler

Characterization of 700 μJ T rays generated during high-power laser solid interaction

Laser-produced solid density plasmas are well-known as table-top sources of electromagnetic radiation. Recent studies have shown that energetic broadband terahertz pulses (T rays) can also be generated from laser-driven compact ion accelerators. Here we report the measurement of record-breaking T-Ray pulses with energies no less than 0.7 mJ. The terahertz spectrum has been characterized for frequencies ranging from 0.1-133 THz. The dependence of T-Ray yield on incident laser energy is linear and shows no tendencies of saturation. The noncollinear emission pattern and the high yield reveal that the T rays are generated by the transient field at the rear surface of the solid target.

Ablation of the cornea by using a low-energy excimer laser

We describe a new multipurpose method for corneal refractive surgery by using a focused excimer laser beam, which allows the application of a small, compact low-energy excimer laser. It is possible to ablate any area desired in the cornea without masking by scanning the focused beam. The ablation depths in freshly enucleated swine eyes were measured in relation to the number of laser pulses (at fixed fluence) and the pulse fluence at wavelengths λ = 248 nm and λ =193 nm. The irradiation conditions were investigated to obtain smooth ablation of the corneal material over an area of about 1 cm2. The experiments show that smooth ablation is obtained when the ratio of the excimer laser beam spot diameter on the corneal surface and the displacement for one scanning step is given by a whole number. A simple model based on rectangular beam profiles is presented to exemplify this.

Photoluminescence investigation of defects after ion-implantation and laser annealing

Abstract Photoluminescence (PL) has been used to study defects in As + and Sb + implanted silicon after laser annealing by a Q switched Nd-glass laser beam. The depth distribution of the defects was determined by measuring the PL signals after successive removal of thin surface layers. The defect generation and transformation is described by a simple kinetic model. From this, depth distributions of defects after ion implantation and laser annealing can be calculated.

Ultra-energetic THz pulses from a laser-driven particle accelerator

Summary form only given. High peak-power THz sources find many applications in material science, non-linear optics and next generation particle accelerators. We report the experimental realization of a gigawatt (GW) class T-rays from a laser-driven particle accelerator. Laser-driven particle accelerators are one of the well studied and promising methods for the generation of energetic particle beams and radiation extending the whole electromagnetic spectrum. Recent studies have shown that powerful T-rays can also be generated during such an interaction [1]. A conversion efficiency of higher than 10-3 and a peak power above a GW makes our source the most efficient and powerful THz source known today.

700μJ THz pulses from a laser-driven particle accelerator

Here we report a laser plasma-driven source of T-rays with the highest pulse energy ever recorded in a laboratory. T-rays are emitted from the rear surface of a solid target in the non-collinear direction at incident laser intensities ~ 1019 W/cm2. Pulse energy measurements reported T-ray pulses with peak energies no less than 700 μJ. Temporal measurements using a single-shot electro-optic method showed the presence of sub-picosecond T-ray pulses with 570 fs duration, thus rendering the peak-power of the source higher even than that of state-of-the-art synchrotrons. A conversion efficiency of higher than 10−3 and an average power of 7 mW makes it the most efficient compact and powerful THz source known today. Spectral analysis revealed the presences of frequencies ranging from 0.1 − 133 THz, while most of the energy is localised in the low frequency region. The dependence of T-ray yield on incident laser energy is linear and shows no signs of saturation. The spatial distribution of the recorded T-rays indicates that most of the T-rays are emitted in the non-collinear direction from the rear-surface of a solid target and the contribution in the forward direction is very small. 2D particle-in-cell simulations show the presence of transient current at the target rear surface.

Enhancement of laser-plasma EUV conversion efficiency by introduction of prepulses

Summary from only given. Until today laser plasma based EUV sources for lithography are still lacking to provide sufficient EUV output power for industrial use. The straight forward way to get more EUV power is to increase the incident laser energy or repetition rate. However, a tricky method is to modify the laser pulse in a way to improve the EUV conversion efficiency from laser radiation into EUV radiation. One way is to use prepulses to create the right preplasma conditions for optimum absorption of the main pulse. We show that by introducing a prepulse the conversion efficiency can be improved within a factor 6-8.

EUV conversion efficiency of laser irradiated water droplets for lithography

Summary form only given. To provide lithographic tools for semiconductor industry which requires the continuing decrease of the smallest structures on computer chips, new technologies have to be investigated. A promising approach is the 13 nm extreme ultraviolet lithography (EUVL). In our case the 13 nm radiation results from the 4d/spl rarr/2p line in fivefold ionized oxygen (O/sup 5+/) emitted by a laser produced plasma. To strongly reduce the debris from the target, with respect to solid bulk targets (e.g.), we used 20 /spl mu/m diameter water droplets. With the right laser energy, we ionized the droplet completely to the desired ionization stage, without leaving behind water contaminating the optics nor overionized plasma. This result is useful in designing a EUV source meeting the high demands of the industry.