By studying the conical emission of a blue femtosecond laser filament in air, it is shown that self-improvement of the beams' spatial mode quality occurs for a self-guided laser pulse.

The near- and off-resonant optical limiting properties of gold, silver and gold–silver alloy nanoparticles in methyl 2-methylprop-2-enoate for nanosecond laser pulses are presented. The nanoparticles are generated by picosecond pulsed laser ablation in liquid having hydrodynamic diameters from 26 to 30 nm. We use a Q-switched Nd:YAG laser working at a wavelength of 1064 or 532 nm, with a pulse width of 3 ns to characterize their behaviour by laser energy and fluence dependent transmittance measurements. To elucidate the contribution of nonlinear scattering to the optical limiting properties the scattered light energy at an angle of 90° is measured. The experimental results show that these nanoparticles have a strong nonlinear attenuation which can be attributed to intraband, interband and free carrier absorption and a thermal-induced scattering only at high input energies. Our results indicate in addition that the surface plasmon resonance does not contribute to the nonlinear processes at high input energies.

, "Laser-induced damage threshold of camera sensors and micro-optoelectromechanical systems," Opt. Eng. 56(3), 034108 (2017), doi: 10.1117/1.OE.56.3.034108. Abstract. The continuous development of laser systems toward more compact and efficient devices constitutes an increasing threat to electro-optical imaging sensors, such as complementary metal-oxide-semiconductors (CMOS) and charge-coupled devices. These types of electronic sensors are used in day-to-day life but also in military or civil security applications. In camera systems dedicated to specific tasks, micro-optoelectromechanical systems, such as a digital micromirror device (DMD), are part of the optical setup. In such systems, the DMD can be located at an intermediate focal plane of the optics and it is also susceptible to laser damage. The goal of our work is to enhance the knowledge of damaging effects on such devices exposed to laser light. The experimental setup for the investigation of laser-induced damage is described in detail. As laser sources, both pulsed lasers and continuous-wave (CW)-lasers are used. The laser-induced damage threshold is determined by the single-shot method by increasing the pulse energy from pulse to pulse or in the case of CW-lasers, by increasing the laser power. Furthermore, we investigate the morphology of laser-induced damage patterns and the dependence of the number of destructive device elements on the laser pulse energy or laser power. In addition to the destruction of single pixels, we observe aftereffects, such as persistent dead columns or rows of pixels in the sensor image.

We present our efforts on estimating light scattering characteristics from commercial off-the-shelf (COTS) camera lenses in order to deduce thereof a set of generic scattering parameters valid for a specific lens class (double Gauss lenses). In previous investigations, we developed a simplified theoretical light scattering model to estimate the irradiance distribution in the focal plane of a camera lens. This theoretical model is based on a 3-parameter bidirectional scattering distribution function (BSDF), which describes light scattering from rough surfaces of the optical elements. Ordinarily, the three scatter parameters of the BSDF are not known for COTS camera lenses, which makes it necessary to assess them by own experiments. Besides the experimental setup and the measurement process, we present in detail the subsequent data exploitation. From measurements on seven COTS camera lenses, we deduced a generic set of scatter parameters. For a deeper analysis, the results of our measurements have also been compared with the output of an optical engineering software. Together with our theoretical model, now stray light calculations can be accomplished even then, when specific scatter parameters are not available from elsewhere. In addition, the light scattering analyses also allow considering the glare vulnerability of optical systems in terms of laser safety.

No abstract