Laser-induced white emission of diamond was investigated under irradiation with a focused beam of an infrared laser diode. It is a surface-related coherent emission, characterized by an excitation threshold and an exponential dependence on pumping laser power. The mechanism of white emission is discussed in terms of multiphoton ionization of carbon atoms in an irradiated spot. The excitation power dependence of white emission intensity has demonstrated hysteresis loop behavior. This phenomenon could be useful in new broadband laser sources and optical information storage.

Freeform surfaces are a new and exciting opportunity in lens design. The technological boundary conditions for manufacturing surfaces with reduced symmetry are complicated. Recently the progress in understanding and controlling this kind of components is ready for use in commercial products. Nearly all procedures of classical design development are changing, if freeform surfaces are used. The mathematical description of the surfaces, the optimization algorithms in lens design and their convergence, the initial design approaches, the evaluation of performance over the field of view, the data transfer in the mechanical design software and in the manufacturing machines, the metrology for characterization of real surfaces and the return of the real surfaces into the simulation are affected. In this contribution, in particular an overview on possible mathematical formulations of the surfaces is given. One of the requirements on the descriptions is a good performance to correct optical aberrations. After fabrication of real surfaces, there are typical deviations seen in the shape. First more localized deformations are observed, which are only poorly described by mode expansions. Therefore a need in describing the surface with localized finite support exists. Secondly the classical diamond turning grinding process typically shows a regular ripple structure. These midfrequency errors are best described by special approaches. For all these cases it would be the best to have simple, robust solutions, that allow for fast calculation in fitting measured surfaces and in raytrace

The increasing use of freeform optical surfaces raises the demand for optical design tools developed for generalized systems. In the design process, surface-by-surface aberration contributions are of special interest. The expansion of the wave aberration function into field- and pupil-dependent coefficients is an analytical method used for that purpose. An alternative numerical approach utilizing data from the trace of multiple ray sets is proposed. The optical system is divided into segments of the optical path measured along the chief ray. Each segment covers one surface and the distance to the subsequent surface. Surface contributions represent the change of the wavefront that occurs due to propagation through individual segments. Further, the surface contributions are divided with respect to their phenomenological origin into intrinsic induced and transfer components. Each component is determined from a separate set of rays. The proposed method does not place any constraints on the system geometry or the aperture shape. However, here we concentrate on near-circular apertures and specify the resulting wavefront error maps using an expansion into Zernike polynomials.

The laser-induced white emission of the graphene-based microchip was investigated under near-infrared region laser irradiation. The emission was characterized by an excitation threshold and an exponential dependence on the pump laser power. A decrease in temperature caused an increase in both the number of absorbed photons and the emission threshold. This dependence can be explained by the multiphoton ionization process in ( sp2, sp3) hybridized domains.

Optical systems can benefit strongly from freeform surfaces, however the choice of the right representation isn` t an easy one. Classical representations like X-Y-polynomials, as well as Zernike-polynomials are often used for such systems, but should have some disadvantage regarding their orthogonality, resulting in worse convergence and reduced quality in final results compared to newer representations like the Q-polynomials by Forbes. Additionally the supported aperture is a circle, which can be a huge drawback in case of optical systems with rectangular aperture. In this case other representations like Chebyshev-or Legendre-polynomials come into focus. There are a larger number of possibilities; however the experience with these newer representations is rather limited. Therefore in this work the focus is on investigating the performance of four widely used representations in optimizing two ambitious systems with very different properties: Three-Mirror-Anastigmat and an anamorphic System. The chosen surface descriptions offer support for circular or rectangular aperture, as well as different grades of departure from rotational symmetry. The basic shapes are for example a conic or best-fit-sphere and the polynomial set is non-, spatial or slope-orthogonal. These surface representations were chosen to evaluate the impact of these aspects on the performance optimization of the two example systems. Freeform descriptions investigated here were XY-polynomials, Zernike in Fringe representation, Q-polynomials by Forbes, as well as 2-dimensional Chebyshev-polynomials. As a result recommendations for the right choice of freeform surface representations for practical issues in the optimization of optical systems can be given