Electronically steered antenna quality mainly relies on the accurate periodicity of the radiating element positions. Very
thin antenna with non-rigid structures will permit the implementation of disruptive mechanical designs and provide
better tactical deployment and permit implementation on non-dedicated platforms. To maintain planar antenna
performances, we propose to dynamically cope with distortions with an innovative method. In this presentation, we will
report on an innovative real-time and embedded measurement technique in harsh environment based on an optical
polarization sensor coupled with an adapted mechanical model, designed in order to maintain a sufficient calibration of
the antenna during its operational use.
Absolute distance measurement using optical feedback with heterodyne detection has been demonstrated by sweeping the optical frequency of a single longitudinal mode (SLM) Yb:Er glass laser. This technique allows enhancing the sensitivity of the laser response to self-mixing thanks to resonant excitation close to the relaxation oscillation frequency peak. The experimental results on a non-cooperative target are in good agreement with the theory. The shape of the resulting signal is analysed both in the temporal and frequency domains considering the specific dynamic of a class B solid-state laser.
Commercial off-the-shelf (COTS) single-mode and multimode germanosilicate optical fibres are intended for use as part of control-command applications in the future Laser Megajoule facility. We evaluated their vulnerability to the radiative environment associated to this project by characterizing their transient radiation responses at infrared wavelengths (1064, 1310 and 1550 nm) after high dose rate exposure (> 108 Gy/s). Our results showed that these COTS fibres exhibit very different transient responses (10-9 s to 1 s after pulse) and permanent damages (times > 1s), depending on the wavelength of transmitted signal and on their compositions. Presented results could be used to define several choices to ensure the functionality of these applications for both shortest times after a shot (10-9 to 103 s) and during the whole LMJ lifetime (30 years).
We examine here the lasing conditions of a Ce :LiCAF laser crystal placed intracavity with a BBO nonlinear crystal and pumped longitudinally throughout an input dichroic mirror by the 532 nm radiation of a frequency-doubled diode-pumped Nd :YAG laser. The comparison with the results obtained with an off-axis configuration shows lower laser slope efficiencies but similar laser performance in terms of threshold absorbed pump fluences (around 200 mJ/cm2). A model based on revisited spectroscopic parameters is developed to account for these laser performance.
The optical feedback into a class B laser can be used as optical velocimeter. This self-mixing technique is simple, self-aligned and very sensitive on low cooperative target. However, the resulting frequency beating only allows deducing the longitudinal speed component along the laser beam. In some cases, such geometry becomes unpractical compared to classical laser Doppler velocimetry (LDV). By using two beams geometry, we have demonstrated the possibility to simultaneously measure both transverse and longitudinal components of the speed vector. This new self-mixing scheme is demonstrated using a single-frequency diode pumped Yb3+:Er3+ phosphate glass laser selected for its inherent very high sensitivity to optical feedback. The principle is validated on a rotating disc with diffusing surface and the tangential linear speed of the disc is precisely measured from 1m/s up to 10m/s without knowing the exact orientation of the disc. Moreover, the technique is spatially selective thanks to the peculiar dynamical response of the laser showing three characteristic beating frequencies in the power spectra when the target is precisely located at the focus point. The dynamic and resolution of the optical sensor are discussed depending on the characteristics of the laser and the geometry of the optical design.
Accurate and highly sensitive speed measurements have been successfully demonstrated by a self-aligned optical feedback velocimetry technique using the self-mixing modulation effect in a double-clad Er-Yb-doped fiber laser.