New control techniques are required to utilize the full potential of next generation high-energy high-repetition-rate pulses lasers while ensuring their safe operation. During automated optimization of an experiment, the control system is required to identify and reject unsafe laser configurations proposed by the optimizer. Using conventional physics codes render impossible when applied to a high energy laser system with 1ms or less time between shots, and also including laser fluctuations and drift. To mitigate this, we are using a deep Bayesian neural network to map the laser’s input power spectrum to its output power spectrum and demonstrate the speed of this approach. The Bayesian neural network can provide an estimate of its own uncertainty as a function of wavelength. A recently developed algorithm enables the uncertainty to be calculated inexpensively using multiple dropout layers inserted into the model. The uncertainty estimates are used by an active learning algorithm to improve the accuracy of the model and intelligently explore the input domain.
A laser system made of two beams of 10 PW each has been designed and is currently built for ELI-NP research infrastructure. Design is presented as well as preliminary results up to the 1PW level amplifier.
In this paper, we present a new photonic technique for producing large time delay of radio-frequency (RF)
modulated optical signals and its application in a novel true-time-delay (TTD) multiple beam-forming system
for wideband RF phased-array antennas using Fourier optics. The RF signal to be delayed is modulated onto
a broadband optical carrier in a frequency-mapped manner by an acousto-optic tunable filter (AOTF). Due to
the phased-matched acousto-optic interaction and the moving nature of the acoustic waves in the AOTF, di.erent
frequency components of the optical carrier are only modulated and Doppler-shifted by the corresponding
frequencies of the modulating RF signal. Heterodyne detection between the modulated optical beam and a timealigned
reference beam from the same light source can recover the modulating RF signal. When a small optical
path length di.erence is introduced between the heterodyne beams, a large RF time delay magnified by the
frequency ratio between the optics and the RF will be generated, which we refer to as the sluggish-light effect.
Sluggish light has potential applications in TTD beam forming for wideband RF phased-array antennas and
proof-of-concept experiments of the sluggish-light based TTD beam forming for an emulated 2- and 4-channel
RF array will be presented in this paper.
In this paper, we present a novel approach for broadband RF photonic signal processing using a femtosecond laser and an Acousto-Optic Tunable Filter (AOTF). We demonstrate that by using spectral filtering in the AOTF, we are able to map each frequency component of the broadband RF signal onto a corresponding set of frequency comb lines of a femtosecond pulse train. The time domain interpretation of this RF to optical frequency mapping yields a femtosecond pulse shaping operation, which is in distinct contrast to the conventional double sideband amplitude modulation of a CW carrier used in RF photonic links. The interaction with a traveling acoustic wave in the AOTF leads to Doppler shift of each frequency comb line by its corresponding RF conterpart, which allows the recovery of the encoded RF signal by heterodyne detection with an unmodulated reference pulse train. As a proof of concept, we experimentally demonstrated mapping of 10 MHz bandwidth RF signals onto 65 nm FWHM optical bandwidth of a 2 GHz repetition rate femtosecond laser using a commercial AOTF and a 40 MHz bandwidth RF signal mapping using a supercontinuum source. Optical processing functions such as RF bandpass/notch filtering can be achieved in the optical domain using optical filters, thereby avoiding the limitations of RF analog filters. Down-conversion naturally occurs based on the laser repetition rate.