Ph. Delaporte

Femtosecond laser for black silicon and photovoltaic cells

We have prepared absorbing structures for photovoltaic cells with different nano-texturization, obtained by means of a femtosecond laser, without the use of corrosive gas (i.e. under vacuum). To take in account the 3D structured front surface, the emitter doping has been realized by using Plasma Immersion Ion Implantation (so-called PULSION). The results show a photocurrent increase up to 60 % in the laser texturized zones.

Analysis of the plasma expansion dynamics by optical time-of-flight measurements

Abstract The laser plasma plume expansion induced by UV nanosecond and IR picosecond irradiation of an Y-Ba-Cu-O target has been studied using optical time-of-flight spectra. Nanosecond ablation leads to a broad particle velocity distribution already at the first stage of expansion because of a temperature dispersion of the ejected species. Picosecond irradiation reduces this kind of dispersion and allows one to observed properly the particle expansion dynamics. The velocities of the charged particles are inversely proportional to the square root of the atomic mass. The velocities of the neutral atoms exhibit much weaker dependence on the atomic mass and are determined by collisional expansion. The time-of-flight spectra reveal a double population of YO + molecules with different velocity distribution.

The so-called dry laser cleaning governed by humidity at the nanometer scale

Illumination with single nanosecond pulses leads to the detachment of silica particles with 250nm radii from silicon surfaces. We identify two laser-energy dependent cleaning regimes by time-of-flight particle-scattering diagnostics. For the higher energies, the ejection of particles is produced by nanoscale ablation due to the laser field enhancement at the particle-surface interface. The damage-free regime at lower energy is shown to be governed by the residual water molecules, which are inevitably trapped on the materials. We discuss the great importance that the humidity plays on the cleaning force and on the adhesion in the experiments.

Applications of laser printing for organic electronics

The development of organic electronic requires a non contact digital printing process. The European funded e-LIFT project investigated the possibility of using the Laser Induced Forward Transfer (LIFT) technique to address this field of applications. This process has been optimized for the deposition of functional organic and inorganic materials in liquid and solid phase, and a set of polymer dynamic release layer (DRL) has been developed to allow a safe transfer of a large range of thin films. Then, some specific applications related to the development of heterogeneous integration in organic electronics have been addressed. We demonstrated the ability of LIFT process to print thin film of organic semiconductor and to realize Organic Thin Film Transistors (OTFT) with mobilities as high as 4 10-2 cm2.V-1.s-1 and Ion/Ioff ratio of 2.8 105. Polymer Light Emitting Diodes (PLED) have been laser printed by transferring in a single step process a stack of thin films, leading to the fabrication of red, blue green PLEDs with luminance ranging from 145 cd.m-2 to 540 cd.m-2. Then, chemical sensors and biosensors have been fabricated by printing polymers and proteins on Surface Acoustic Wave (SAW) devices. The ability of LIFT to transfer several sensing elements on a same device with high resolution allows improving the selectivity of these sensors and biosensors. Gas sensors based on the deposition of semiconducting oxide (SnO2) and biosensors for the detection of herbicides relying on the printing of proteins have also been realized and their performances overcome those of commercial devices. At last, we successfully laser-printed thermoelectric materials and realized microgenerators for energy harvesting applications.

Long pulse KrCl excimer laser at 222 nm

A long pulse (up to 185 ns FWHM) KrCl laser at λ=222 nm has been achieved by combining x‐ray preionization and double discharge (spiker/sustainer) with fast ferrite magnetic switch. A relatively low pumping power (0.5 to 1 MW/cm3) and 25 cm gain length allows a maximum extracted energy of 115 mJ in 135 ns FWHM, with an overall energy efficiency of 0.75%.

XeF(C–A) laser pumped by formed-ferrite open discharge radiation

A study of a high-power blue–green XeF(C–A) laser photolytically pumped by an open discharge along a formed-ferrite surface is presented. A laser output energy of 1.3 J was extracted from a gas mixture of 4 Torr XeF2, 230 Torr N2, and 680 Torr Kr, with a stable optical resonator. With a flat optical resonator, a laser output energy of 1 J was obtained. In this case, we observed an oscillating regime of the laser power, which indicates that the unsaturated gain value was close to the laser action threshold. Perspectives of optical pumping schemes are presented.

Interaction between jets during laser-induced forward transfer

Simultaneous two-beam laser-induced forward transfer (LIFT) was carried out for various inter-beam separations, analyzing both the resulting printing outcomes and the corresponding liquid transfer dynamics. In a first experiment, droplets of an aqueous solution were printed onto a substrate at different inter-beam distances, which proved that a significant departure from the single-beam LIFT dynamics takes places at specific separations. In the second experiment, time-resolved imaging analysis revealed the existence of significant jet-jet interactions at those separations; such interactions proceed through a dynamics that results in remarkable jet deflection for which a possible onset mechanism is proposed.

XeCl laser treatment of steel surface

Due to the UV radiation properties such as high surface adsorption and high photon energies, excimer laser are well adapted for surface treatment. UV laser irradiation of a surface with a fluence high enough induces the ejection of particles from the surface (through ablation process). In many cases, laser treatment results are more complex than simple ablation. We studied the effects of excimer laser (XeCl) irradiation of steel surface on its chemical properties. To investigate the induced surface changes, we have used Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). XPS and AES analyses show that the laser treatment induces the apparition of a Fe2O3 layer at the surface instead of FeOOH for an untreated surface. The evolution of the chemical properties of the surface has been studied as a function of the air exposure duration after the laser treatment.

Waves Behaviour In A High Repetition High Average Power Excimer Laser

Experimental study of waves behaviour in a high repetition rate excimer laser has been undertaken. Excitation of active medium in a subsonic loop is achieved by means of a classical discharge, through transfer capacitors. The discharge stability is controlled by a wire ion plasma (w.i.p.) X-rays gun. The strong acoustic waves induced by the active medium excitation are analysed by means of a Michelson interferometer and fast pressure transducers.

Small volume long pulse X-ray preionized XeCl laser with double discharge and fast ferrite magnetic switch

Abstract A long pulse, high efficiency X-ray preionized discharge XeCl laser has been obtained with a Ne/Xe/HCl mixture at 2.3 atm pressure in a 50 cm 3 active volume, for a 25 cm gain length, by combining double discharge technique (spiker/sustainer) with a new fast ferrite magnetic switch. An efficiency of 3%, with 120mJ extracted optical energy in a 140 ns (fwhm) laser pulse length, has been demonstrated.