Non-linear optical frequency conversion crystals for space applications

Abstract

Reliable, long term operation of high-power laser systems in the Earth orbit is not a straightforward task as the space environment entails various risks for optical surfaces and bulk materials. The increased operational risk is, among others, due to the presence of high energy radiation penetrating the metallic shielding of satellites and inducing absorption centers in the bulk of optical components, and vacuum exposure which can deteriorate coating performance. Comprehensive testing for analyzing high-energy radiation effects and mitigation procedures were performed on a set of frequency conversion crystals and are discussed in this paper. In addition to a general resistance to space environmental effects, the frequency conversion crystals were subjected to a comparative analysis on optimum third harmonic efficiency, starting from pulsed 1064 nm laser radiation, with the goal of exceeding a value of 30 %. Concomitant modeling supported the selection of crystal parameters and the definition of crystal dimensions.

Gamma irradiation-induced absorption in single-domain and periodically-poled KTiOPO_4 and Rb:KTiOPO_4

“…Comparison of the induced absorption measured in our experiments with the measurements reported in the literature [32][33][34] indicates that the absolute value of the induced absorption depends much stronger on the gamma radiation dose rate than on the cumulative dose. That would be the case if the processes of free carrier generation, recombination as well as color center self-annealing by the generated phonons are competing.…”

“…Three dosages were chosen, specifically 10, 30 and 100 krad in accordance to the testing recommendations by the European Space Agency [39]. Moreover, similar doses have been used in the previous experiments reported in the literature [32,33].…”

“…The radiation can create free carriers and introduce new defects in the nonlinear materials which, in turn give rise to additional linear absorption and leads to degradation of the device performance. The influence of gamma and proton radiation on transmission properties in commercially tradeable KTP and other nonlinear crystals has been previously studied with the focus on second-harmonic generation at 532 nm [32,33]. It was found that the SHG efficiency decreased by about 15% after exposure to 139 krad dose of gamma radiation, primarily caused by the decrease in the linear transmission in the spectral range around 500 nm.…”

Optomechanical design and construction of a vacuum-compatible optical parametric oscillator for generation of squeezed light

“…While previous work has described single pass nonlinear sources operating under high vacuum, [8][9][10] this work describes the techniques necessary to build a doubly resonant travelling wave optical parametric oscillator (OPO) with a near monolithic glass construction. The bow-tie OPO design has a large degree of optical isolation (40 dB) 11 and has produced the highest levels of squeezing at acoustic frequencies.…”

A squeezed light source operated under high vacuum

“…Applications such as improving the sensitivity of advanced gravitational wave detectors 8 and the development of space-based quantum networks 9 will require field-deployable, vacuum-compatible non-classical light sources. To date non-linear photonics devices operated under high vacuum have been simple single pass systems, testing harmonic generation 10 11 and the production of classically correlated photon pairs 12 for space-based applications. Here we demonstrate the production under high-vacuum conditions of non-classical squeezed light with an observed 8.6 dB of quantum noise reduction down to 10 Hz.…”