Design of an efficient illuminator for partially coherent sources in the extreme ultraviolet.

In this paper, the design of an efficient illuminator for extreme ultraviolet (EUV) applications such as photolithography, metrology, and microscopy is investigated. Illuminators are arrangements of optical components that allow us to tailor optical parameters to a targeted application. For the EUV spectral range, illuminators are commonly realized by an arrangement of several multilayer mirrors.

Automated lens design for optical systems consisting of stock lenses.

The design of lens systems requires advanced knowledge and the mastery of highly specialized software tools. Furthermore, for the realization of the designed lens systems often custom-made lenses are needed, which are expensive and have lead times of several weeks compared to stock lenses with several days. To shorten realization time, a new approach for the automated design of lens systems consisting of stock lenses is developed.

Rigorous approach for unifying wave optics and state of the art rendering techniques.

With the capabilities of diffractive optics there is a rising demand for determining the light interaction of diffractive elements with arbitrary illumination and scenery. Since the structured surfaces' scale lies within the visible wavelengths and below, the light's interaction cannot be simulated with state of the art geometric optic rendering approaches. This paper presents a new model for the inclusion of wave-optical effects into Monte Carlo path rendering concepts.

Freeform optics design for extended sources in paraxial approximation exploiting the expectation maximization algorithm.

Freeform optics generating specific irradiance distributions have been used in various applications for some time now. While most freeform optics design algorithms assume point sources or perfectly collimated light, the search for algorithms for non-idealized light sources with finite spatial as well as angular extent is still ongoing. In this work, such an approach is presented where the resulting irradiance distribution of a freeform optical surface is calculated as a superposition of pinhole images generated by points on the optical surface.

Characterization of nanoscale gratings by spectroscopic reflectometry in the extreme ultraviolet with a stand-alone setup.

The authors present a study on the dimensional characterization of nanoscale line gratings by spectroscopic reflectometry in the extreme ultraviolet spectral range (5 nm to 20 nm wavelength). The investigated grating parameters include the line height, the line width, the sidewall angle and corner radii. The study demonstrates that the utilization of shorter wavelengths in state-of-the-art optical scatterometry provides a high sensitivity with respect to the geometrical dimensions of nanoscale gratings.

Structural properties of templated Ge quantum dot arrays: impact of growth and pre-pattern parameters.

In this study we analyze the impact of process and growth parameters on the structural properties of germanium (Ge) quantum dot (QD) arrays. The arrays were deposited by molecular-beam epitaxy on pre-patterned silicon (Si) substrates. Periodic arrays of pits with diameters between 120 and 20 nm and pitches ranging from 200 nm down to 40 nm were etched into the substrate prior to growth.

Design of structured YAG:Ce scintillators with enhanced outcoupling for image detection in the extreme ultraviolet.

In this Letter, the authors present a design study on YAG:Ce scintillator plates with a microstructured and coated surface. The goal of the study is to improve the outcoupling efficiency and to optimize the directionality of the scintillation light with respect to indirect image detection in the extreme ultraviolet spectral range (5-50 nm wavelength). In a geometric optical simulation, a gain in outcoupling efficiency by over a factor of 4 is shown while the directionality of the scintillation light is improved with respect to state-of-the-art plane scintillator plates.

Laser cutting of bone tissue under bulk water with a pulsed ps-laser at 532 nm.

Hard-tissue ablation was already investigated for a broad variety of pulsed laser systems, which cover almost the entire range of available wavelengths and pulse parameters. Most effective in hard-tissue ablation are Er:YAG and CO2 lasers, both utilizing the effect of absorption of infrared wavelengths by water and so-called explosive vaporization, when a thin water film or water–air spray is supplied. The typical flow rates and the water layer thicknesses are too low for surgical applications where bleeding occurs and wound flushing is necessary.

Designing optical free-form surfaces for extended sources.

LED lighting has been a strongly growing field for the last decade. The outstanding features of LED, like compactness and low operating temperature take the control of light distributions to a new level. Key for this is the development of sophisticated optical elements that distribute the light as intended.

Optical set-up for dynamic superposition of three laser beams for structuring and polishing applications.

Structuring by remelting is an innovative approach for structuring metallic surfaces with laser radiation, where no material is removed but reallocated while molten. Based on this remelting principle an innovative structuring technique is investigated, where laser beams are superposed. A melt pool is generated by a cw laser beam with constant feed rate.

39.1 μJ picosecond ultraviolet pulses at 355 nm with 1 MHz repeat rate.

Based on our reliable high-power picosecond laser source with high beam qualities, we designed a compact and efficient third harmonic generation scheme by cascading a frequency doubling and a sum frequency generation using LBO as the nonlinear material. A maximum output of 39.1 W with a repeat rate of 1 MHz at 355 nm was obtained, which implied a pulse energy of 39.

Deformation of ultra-short laser pulses by optical systems for laser scanners.

Current experiments of processing glass with ultra-short laser pulses (< 1 ps) lead to scan angle depending processing results. This scan angle depending effect is examined by simulations of a common focusing lens for laser scanners. Due to dispersion, focusing lenses may cause pulse deformations and increase the pulse duration in the focal region.

Limitations of the ray mapping approach in freeform optics design.

It was previously demonstrated by Bäuerle et al. [Opt. Express20, 14477 (2012)] that the computation of ray paths through the optical system (ray mapping) can be used to design multisurface freeform optical elements creating a prescribed irradiance pattern for a zero-étendue source.

High resolution irradiance tailoring using multiple freeform surfaces.

More and more lighting applications require the design of dedicated optics to achieve a given radiant intensity or irradiance distribution. Freeform optics has the advantage of providing such a functionality with a compact design. It was previously demonstrated in [Bäuerle et al.

Using adaptive weighted least squares approximation for coupling thermal and optical simulation.

Thermo-optical simulation is a mandatory enhancement of classical ray tracing, since nowadays many fields in the branch of optical technology have to deal with thermal effects. This paper discusses an approach for coupling the finite element method (FEM) and ray tracing simulation by processing finite element (FE) data using scattered data approximation techniques, particularly with an adaptive weighted least squares approximation algorithm in two dimensions. The validation of the implemented interface is being conducted by comparing approximated data to analytical functions.

Algorithm for irradiance tailoring using multiple freeform optical surfaces.

The design of freeform lenses and reflectors allows to achieve non-radially symmetric irradiance distributions whilst keeping the optical system compact. In the case of a point-like source, such as an LED, it is often desired to capture a wide angle of source light in order to increase optical efficiency. This generally results in strongly curved optics, requiring both lens surfaces to contribute to the total ray refraction, and thereby minimising Fresnel losses.

Mach-Zehnder interference microscopy optically records electrically stimulated cellular activity in unstained nerve cells.

Dual-beam white light interference microscopy monitors changes in the optical density of the investigated object with high sensitivity. We report on the recording of dynamic changes in a neuron's optical density evoked by extracellular electrical stimulation. These recorded changes were analysed and unambiguously connected to the investigated object, an invertebrate neuron of the pond snail Lymnaea stagnalis.

Neodymium:YAG 30-W cw Laser Side Pumped by Three Diode Laser Bars.

A theoretical calculation of pump power deposition in a direct water-cooled Nd:YAG laser rod, side pumped by three diode laser bars is presented. The pumping cavity design provides a nearly uniform pump profile. More than 30-W cw output power with optical-to-optical efficiencies of more than 30% are obtained.

Polarization characteristics of a Nd:YAG laser side pumped by diode laser bars.

A detailed experimental investigation of the polarization characteristics of a diode laser side-pumped Nd:YAG laser has been performed. A Brewster plate inserted into the cavity resulted in a decrease of 50% of the output power that is due to depolarization. A thin-film polarizer (TFP) was introduced into the cavity and the depolarization loss served as the output coupling.

Partially end-pumped Nd:YAG slab laser with a hybrid resonator.

A Nd:YAG slab is partially end pumped by a diode laser stack with three diode laser bars. The pumped volume has a rectangular cross section. A hybrid resonator, which is stable in the plane of small dimension and is off-axis unstable in the plane of large dimension of the gain cross section, was used to yield highly efficient laser operation at diffraction-limited beam quality.

Heat transport in solid and air-clad fibers for high-power fiber lasers.

An analytical approach for the thermal design for high-power fiber lasers and fiber components is presented. The approach is based on defining a thermal resistance for each fiber layer. Thus the importance of each layer for the heat transport is made transparent and the influence of the parameters can be studied for each layer separately.

Diode-pumped efficient slab laser with two Nd:YLF crystals and second-harmonic generation by slab LBO.

We demonstrate a diode-pumped electro-optical Q-switched slab laser with a high optical efficiency, high pulse energy, and short pulse width with two Nd:YLF crystals inside one resonator. The single compact slab resonator can generate a 1D top-hat beam at both the far field and the near field. With a slab-geometry-design lithium triborate (LBO) crystal, efficient critical phase-matching second-harmonic generation for a 1D top-hat beam with multiple transverse modes is achieved.

Serial cerebrospinal fluid tryptophan and 5-hydroxy indoleacetic acid concentrations in healthy human subjects.

The role of the serotonergic system in the pathogenesis of behavioral disorders such as depression, alcoholism, obsessive-compulsive disorder, and violence is not completely understood. Measurement of the concentration of neurotransmitters and their metabolites in cerebrospinal fluid (CSF) is considered among the most valid, albeit indirect, methods of assessing central nervous system function in man. However, most studies in humans have measured lumbar CSF concentrations only at single time points, thus not taking into account rhythmic or episodic variations in levels of neurotransmitters, precursors, or metabolites.

The effect of feeding on cerebrospinal fluid corticotropin-releasing hormone levels in humans.

Corticotropin-releasing hormone (CRH) is a neuropeptide thought to play a role in appetite regulation. In this report, we used a serial cerebrospinal fluid (CSF) sampling technique to examine the relationship between CSF CRH, plasma ACTH and cortisol and perceptions of hunger and satiety in fasting and sated volunteers. CSF was withdrawn continuously from 11:00 AM to 5:00 PM via an indwelling subarachnoid catheter.

Serum thyrotropin concentrations and bioactivity during sleep deprivation in depression.

Background: One night of sleep deprivation induces a brief remission in about half of depressed patients. Subclinical hypothyroidism may be associated with depression, and changes in hypothalamic-pituitary-thyroid function may affect the mood response to sleep deprivation. We wished to define precisely the status of the hypothalamic-pituitary-thyroid axis of depressed patients during sleep deprivation and the possible relationship of hypothalamic-pituitary-thyroid function to the mood response.