Long distance laser filamentation using Yb:YAG kHz laser.

In the framework of the Laser Lightning Rod project, whose aim is to show that laser-induced filaments can guide lightning discharges over considerable distances, we study over a distance of 140 m the filaments created by a laser system with J-range pulses of 1 ps duration at 1 kHz repetition rate. We investigate the spatial evolution of the multiple filamentation regime using the fundamental beam at 1030 nm or using combination with the second and third harmonics. The measurements were made using both a collimated beam and a loosely focused beam.

Laser-guided lightning.

Lightning discharges between charged clouds and the Earth's surface are responsible for considerable damages and casualties. It is therefore important to develop better protection methods in addition to the traditional Franklin rod. Here we present the first demonstration that laser-induced filaments-formed in the sky by short and intense laser pulses-can guide lightning discharges over considerable distances. We believe that this experimental breakthrough will lead to progress in lightning protection and lightning physics. An experimental campaign was conducted on the Säntis mountain in north-eastern Switzerland during the summer of 2021 with a high-repetition-rate terawatt laser. The guiding of an upward negative lightning leader over a distance of 50 m was recorded by two separate high-speed cameras. The guiding of negative lightning leaders by laser filaments was corroborated in three other instances by very-high-frequency interferometric measurements, and the number of X-ray bursts detected during guided lightning events greatly increased. Although this research field has been very active for more than 20 years, this is the first field-result that experimentally demonstrates lightning guided by lasers. This work paves the way for new atmospheric applications of ultrashort lasers and represents an important step forward in the development of a laser based lightning protection for airports, launchpads or large infrastructures.

Non-linear photochemical pathways in laser-induced atmospheric aerosol formation.

We measured the chemical composition and the size distribution of aerosols generated by femtosecond-Terawatt laser pulses in the atmosphere using an aerosol mass spectrometer (AMS). We show that nitric acid condenses in the form of ammonium nitrate, and that oxidized volatile organics also contribute to particle growth. These two components account for two thirds and one third, respectively, of the dry laser-condensed mass. They appear in two different modes centred at 380 nm and 150 nm. The number concentration of particles between 25 and 300 nm increases by a factor of 15. Pre-existing water droplets strongly increase the oxidative properties of the laser-activated atmosphere, substantially enhancing the condensation of organics under laser illumination.

High-power potassium-titanyl-phosphate laser fibres for endovaporization of benign prostatic hyperplasia: how much do they deteriorate during the procedure?

OBJECTIVE: • To assess the residual power delivered at the tip of a high-power (80 W) potassium-titanyl-phosphate (KTP) laser (80 W Green Light PV(TM), Laserscope(®); American Medical Systems, Minnetonka, MN, USA) at the end of a photoselective vaporization of the prostate (PVP) procedure, as well as the deflection angle of the laser beam. MATERIALS AND METHODS: • In total, 65 laser fibres were collected at the end of PVP procedures indicated for symptomatic benign prostatic hyperplasia over a period of 17 months. PVP was performed by two senior urologists. • The power of laser beam at tip exit was measured for each fibre at the end of the procedures using a photodiode whose signal was amplified, and then quantified by a volt multimeter. • The deflection angle was measured using a graduated sphere. RESULTS: • Approximately 70% of fibres delivered less than 40 W at the end of the procedure, which is less than the vaporization threshold. • Some 9% of fibres had lost their diffraction capacity with a significant alteration of laser beam angulation. These values were not operator dependent. CONCLUSIONS: • The data show that a large proportion of laser fibers deliver a significantly underpowered beam at the end of the procedures. • This seems to be caused by peroperative destruction of the fibers, which results in a progressive loss of efficacy of PVP during procedures.