Romain Czarny’s scientific contributions

ThomX is a compact x-ray source based on Compton scattering, installed at IJCLab (Laboratoire de physique des 2 infinis-Irène Joliot-Curie) in Orsay. The machine uses a small electron storage ring and an intense laser pulse stored in a high-finesse optical cavity. This article describes the various subsystems of the machine and their initial results of the commissioning, which began in mid-2021. This first commissioning phase led to the production of 10 10 x-rays/s with an on-axis energy of 45 keV. The main steps to be taken to reach the nominal flux are outlined at the end. Published by the American Physical Society 2025

We report on a high-average-power 888 nm diode-pumped passively mode-locked TEM00 Nd:YVO4 oscillator with adjustable pulse durations. From 45 to 15 W output power, we produced corresponding 32 to 12 ps long pulses without spatial hole burning.

We report on a high-power passively mode-locked TEM 00 Nd : Y V O 4 oscillator, 888 nm diode-pumped, with pulse durations adjustable between 46 ps and 12 ps . The duration tunability was obtained by varying the output coupler (OC) transmission while avoiding resorting to spatial hole burning (SHB) for pulse shortening. At a repetition rate of 91 MHz and for an output power ranging from 15 W to 45 W , we produced SHB-free 12 - ps - to 32 - ps -long pulses. Within this range of power, these are the shortest pulse durations obtained directly from Nd : Y V O 4 oscillators.

We report on a high-power, passively mode-locked, TEM00 Nd:YVO4 oscillator with adjustable pulse duration between 46 and 12ps. The laser is end-pumped by an 888nm laser diode and mode-locking is achieved with a semiconductor saturable absorber mirror (SESAM). The laser has a repetition rate of 91MHz and the M2 beam quality factor is better than 1.2 at 15ps. At the optimum output coupler, it provides a maximum average output power of 45W with 32ps pulse duration. In literature, the presence of spatial hole burning (SHB) often helps to shorten the pulse length down to few picoseconds. However, SHB might be an issue for some specific application requiring e.g. low noise picosecond oscillators. In this contribution, we demonstrate that it is possible to shorten the pulse duration by lowering the intracavity losses without SHB. Pulse tunability from 46 to 12ps is achieved by changing the output coupler of the cavity while staying in the continuous-wave mode-locked regime. Pulse duration is almost linear with the output coupler transmission and increases from 12 to 32ps with average output power ranging from 15 to 45W. In this range of output power, we demonstrate the shortest pulses directly from a Nd:YVO4 oscillator.

A high-power semiconductor saturable absorber mirror (SESAM)-passively modelocked TEM₀₀ Nd:YAG oscillator based on a diode-side-pumped single laser head is reported. This laser provides 21.4 W of average power at a repetition-rate of 82 MHz with 18 ps pulse duration. This laser could be an essential part in future high flux monochromatic compact X-ray source systems.

A design for a 20 W-sub-20 ps class mode-locked Nd:YAG oscillator is proposed.It demonstrates that Nd:YAG still has the potential to produce higher average power picosecond pulses with a single oscillator laser head and might be a good candidate to be part of a high flux compact X-ray source.

The goal of this project is to develop a compact device which can produce an intense flux of monochromatic X- rays for medical applications. It is based on Compton back-scattering resulting from collisions between laser pulses and relativistic electron bunches. Intense laser beams can be obtained with a high gain Fabry-Perot cavity coupled with either a high average power fiber amplifier or a high average power conventional bulk amplifier. Such a scheme is going to be developed by CELIA, Thalès and LAL laboratories. The accelerator design to produce high repetition rate electron bunches at 50 MeV is under study. Two possibilities are being investigated: either a storage ring operating at an injection frequency high enough to preserve the electron beam characteristics or a high average current ERL. Both accelerator configurations aiming at producing X-ray fluxes higher than 10^12 photons/s will be presented.