CC BY
15LS-I-12
HORIZON Laser: a new generation of kW-class ps amplifier
J. Lhermite*, C.Feral, D. Marion, A. Rohm, Ph. Balcou D. Descamps, S. Petit, M.C. Nadeau, E. Mevel
Universite de Bordeaux-C.N.R.S.-C.E.A., Centre Lasers Intenses etApplications (CELIA), UMR 5107,
33405 Talence, France
jerome.lhermite@u-bordeaux.fr
The LEAP project, with the Horizon laser, aims at the ambitious performance of 1 J at 1 kHz with a pulse duration of 1 ps, corresponding to an average power of 1 kW [1]. Many applications are on demand of high power levels and high repetition rate picosecond lasers such as secondary sources development (e.g. X-rays for medical applications) or space debris ranging to detect smaller and further objects. One of the main difficulties related to the generation of such power levels is the thermal management in the main amplifier. In our configuration, the laser gain medium is Yb:YAG to ensure amplification around 1030 nm. Contrary to other international projects aiming at kW/kHz operation using technologies such as thin disks [2] or cryogenically cooled amplifiers [3], we developed a new architecture of high power amplifiers, based on an original method of thermal management. The strategy we are implementing combines three aspects intended to manage the thermal load. To distribute the heat, we use three cascaded 70 mm diameter Yb:YAG crystals with a thickness varying between 2 and 3 mm (Fig. 1). These disks are then immersed in a circulating fluid and rotated in order to spread the thermal load on a ring which limits the temperature rise of the disks below 50°C.
Fig 1 : The three Yb:YAG spinning disks Fig 2: First gain measurements of the spinning head in CW
regime for different input power levels
Due to the low single pass expected efficiency according to the simulations (around 1.4), the laser head is implemented in an 8-pass configuration. We recently measured the first gain values in continuous wave (CW) regime and with a pump level of 3 kW at 940 nm for a first step (Fig.2). The pump will be increased up to 13 kW in the second phase of our development coupled to a pulsed seeder delivering 100 mJ at 1 kHz.
Experimentally, the single pass gain reaches 1.35 which is in good agreement with the simulations. In 8-pass configuration, a small-signal gain of 10 has been measured. We observe a saturation of this gain at higher input power due to the small size of the spot signal and the mismatch with the pump spot size. These parameters are being optimized to allow the final objective of 1 J at 1 kHz.
[1] S. Petit, C. Feral, M.-C. Nadeau, P. Balcou, J. Brandam, D. Descamps, J. Lhermite, and D. Marion, "Towards a kW-class picosecond laser at 1 kHz," Conference on Lasers and Electro-Optics and European Quantum Electronics Conference (CLEO-EQEC), Munich, Germany, 2019, p. ca_8_6.
[2] C. Herkommer, P. Krotz, R. Jung, S. Klingebiel, C. Wandt, R. Bessing, P. Walch, T. Produit, K. Michel, D. Bauer, R. Kienberger, and T. Metzger, "Ultrafast thin-disk multipass amplifier with 720 mJ operating at kilohertz repetition rate for applications in atmospheric research," Opt. Exp., vol. 28, pp. 30164-30173, 2020
[3] Yong Wang, Han Chi, Cory Baumgarten, Kristian Dehne, Alexander R. Meadows, Aaron Davenport, Gabe Murray, Brendan A. Reagan, Carmen S. Menoni, and Jorge J. Rocca, "1.1 J Yb:YAG picosecond laser at 1 kHz repetition rate," Opt. Lett. 45, 6615-6618 (2020)
