We report a passively Q-switched two-component visible laser light source based on frequency conversion. The device
consists of a monolithic single transverse mode ridge-waveguide infrared laser diode and a waveguide-type periodically
poled magnesium oxide doped lithium niobate crystal for second harmonic light generation. An integrated 45-degree
folding mirror and a coupling lens are formed by etching on opposite sides of the monolithic gallium arsenide -based
laser diode for coupling the infrared emission into the waveguide-type nonlinear crystal for efficient single pass
frequency conversion. Passively Q-switched operation is realized by an integrated electro-absorber section coupled with
the in-plane multi-quantum well gain structure. Stable high-repetition rate self-pulsating operation was achieved by
reverse-biasing the electro-absorber section and reduced speckle visibility of the second harmonic light was observed
when compared to continuous-wave operation of the same laser.
We report a fast-switching two-component frequency-converted laser with reduced speckle visibility. A bottom-emitting
passively Q-switched laser with integrated electroabsorber, folding mirror and coupling lens was successfully applied
with a waveguide-type periodically poled magnesium oxide doped lithium niobate crystal to generate second harmonic
light at 532 nm. Reduced speckle visibility was demonstrated when operating the laser in self-pulsating mode when
compared to continuous-wave operation even when using a nonlinear crystal with narrow acceptance bandwidth of 0.24
nm @ 1064 nm. The spectral width of the infrared light was 0.33 nm in pulsed mode and 0.08 nm in continuous-wave
mode resulting in visible light spectral width of 0.12 nm and 0.03 nm in self-pulsating and continuous-wave mode.
Planar chirality can lead to interesting polarization effects whose interpretation has invoked possible violation of reciprocity and time reversality. We show that a quasi-two-dimensional array consisting of gold nanoparticles with no symmetry plane and having sub-wavelength periodicity and thickness exhibits giant specific rotation (~10<sup>4</sup> °/mm) at normal incidence. The rotation is the same for light incident on the front and back sides of the sample. Such reciprocity manifests three-dimensionality of the structure arising from the asymmetry of light-plasmon coupling at the air-metal and substrate-metal interfaces of the structure. The structures thus enable nanoscale polarization control but violate no symmetry principle.
Electromagnetic optimization is applied to four level surface relief gratings to obtain high diffraction effciencies over wide spectral ranges. The results are compared with the classical designs and proved superior. Significant improvements in the diffraction efficiency or independence of the incident wavelength can be obtained.
A review of electromagnetic models for the analysis of complex microstructures for controlling optical fields is provided. An overview of the most useful rigorous approaches and indications of their computational complexity as well as their domain of applicability is first presented. Then two types of approximate electromagnetic approaches are discusses: local interface techniques and local perturbation methods. These are compared to rigorous methods with a view on computational complexity and domain of applicability.
We apply transmission gratings under Littrow incidence to produce polychromatic colors by additive color mixing. Parametric optimization of gratings is employed to confirm high efficiency. In addition, we show that the system can yield the same color from two different light sources with arbitrary spectra, i.e. system can produce metameric colors.
Design and manufacturing of diffractive optical elements (DOEs) are presented. Mass replication methods for DOEs are explained including UV-replication, micro-injection moulding and reel-to-reel production. Novel applications of diffractive optics including spectroscopic surface relief gratings, antireflection surfaces, infrared light rejection gratings, light incoupling into thin waveguides, and additive diffractive colour mixing are presented.
Antireflection coatings are studied for increasing the transmitted efficiency of diffractive optical elements. Numerical simulations of different beam-splitters show that noticeable increase in efficiency can be reached with a particular optimized structure.
Perturbations arising from sharp discontinuities of surface relief
profiles can have significant effects on the field transmitted through diffractive structures. A method utilizing these perturbations is presented for efficient analysis of the response of surface profiles in the non-paraxial domain. Comparison with rigorous diffraction theory proves the method reliable and the numerical feasibility of the approach is much better than that of
Metallic nanostructures can have strong effects on the polarization state of light and present significant polarization sensitivity. However, quite often these phenomena have only negligible effects thus passing our attention without careful analysis. We show that these effects can be enhanced by using resonance effects arising from waveguide modes propagating along the surface. This enables the use of metallic nanostructures as artificial media components modulating the polarization state of light.
Recent interest in the study of metal nanoparticles and related structures has greatly increased. Technologies such as electron beam lithography facilitate the fabrication of such subwavelength structures. Much research has focused on the linear optical properties of high-symmetry particles, such as ellipsoids and spheroids. However, we focus on both the linear and nonlinear optical responses of low-symmetry L-shaped nanoparticles. We show that these nanoparticle arrays are exceptionally sensitive to polarization. Small asymmetries in the particle shapes lead to large deviations in the primary extinction directions from expected locations. The structural asymmetries may also induce optical activity. We present results of detailed polarization analysis through second-harmonic generation experiments that are based on symmetry arguments regarding the second-order susceptibility tensor. The results confirm that the structural deviations from the ideal shape lead to further breakdown in the symmetry properties of the arrays.
Diffractive components in X-ray and UV regions have several attractive applications, but analysis in those regions has not been thoroughly investigated. Besides, in the X-ray and UV regions the complex refractive indices of metals differ substantially from the values in the visible region of the spectrum. The consequences of this phenomenon are analyzed for metallic structures illuminated by wavelengths ranging from infrared to soft X-rays. The rigorous diffraction theory and the thin element approximation is applied to study the behavior of both wire-grid polarizers and inductive grid filters. Single layer film theory is used to enhance the reliability of the thin element approximation.
Local Spherical Interface Approximation (LSIA) for modelling the propagation of electromagnetic wave fields through analog interfaces is introduced. The method belongs to a class of Local Elementary Interface Approximation (LEIA) in which the propagation is modelled by decomposing the field into local elementary fields. In the method introduced here both the phase-distribution of the field and the boundary of discontinuity are assumed to be locally spherical, which enables the use of Coddington's equations in the determination of the reflected and transmitted fields. The amplitude reflection and transmission is treated with the help of the intensity law of geometrical optics and the energy conservation law. Convergence comparison between LSIA and Local Plane Interface Approximation (LPIA) is performed for a sinusoidal diffraction grating. The accuracy of the method is illustrated with a numerical example.