We developed a novel LED projection based direct write grayscale lithography system for the generation of optical surface profiles such as micro-lenses, diffractive elements, diffusors, and micro freeforms. The image formation is realized by a LCoS micro-display which is illuminated by a 405 nm UV High Power LED. The image on the display can be demagnified from factors 5x to 100x with an exchangeable lens. By controlling exposure time and LED power, the presented technique enables a highly dynamic dosage control for the exposure of h-line sensitive photo resist. In addition, the LCoS micro-display allows for an intensity control within the micro-image which is particularly advantageous to eliminate surface profile errors from stitching and limited homogeneity from LED illumination. Together with an accurate calibration of the resist response this leads to a superior low surface error of realized profiles below <0.2% RMS. The micro-display is mounted on a 3-axis (XYθ) stage for precise alignment. The substrate is brought into position with an air bearing stage which addresses an area of 500 × 500 mm2 with a positioning accuracy of <100 nm. As the exposure setup performs controlled motion in the z-direction the system to maintain the focal distance and lithographic patterning on non-planar surfaces to some extent. The exposure concept allows a high structure depth of more than 100 μm and a spatial resolution below 1 μm as well as the possibility of very steep sidewalls with angles larger than >80°. Another benefit of the approach is a patterning speed up to 100 cm2/h, which allows fabricating large-scale optics and microstructures in an acceptable time. We present the setup and show examples of micro-structures to demonstrate the performance of the system, namely a refractive freeform array, where the RMS surface deviation does not exceed 0.2% of the total structure depth of 75 μm. Furthermore, we show that this exposure tool is suitable to generate diffractive optical elements as well as freeform optics and arrays with a high aspect ratio and structure depth showing a superior optical performance. Lastly we demonstrate a multi-level diffraction grating on a curved substrate.
The combination of a 10.6 μm main pulse CO2 laser and a 1064 nm pre-pulse Nd:YAG laser in EUV source concepts for HVM would require collector mirrors with an integrated spectral purity filter that suppresses both laser wavelengths. This paper discusses a new approach of a dual-wavelength spectral purity filter to suppress 10.6 μm and 1064 nm IR radiation at the same time. The dual-wavelength spectral purity filter combines two binary phase gratings that are optimized for 10.6 μm and 1064 nm, respectively. The dual phase grating structure has been realized on spherical sub-aperture EUV collector mirrors having an outer diameter of 150 mm. IR suppression factors of 260 at 10.6 μm and 620 at 1064 nm have been measured on the sub-aperture EUV collector while its EUV reflectance exceeded 64 % at 13.5 nm.
Miniaturization and higher integration of opto-electronic components require highly sophisticated optical designs. This creates the demand for freeform technologies like Two-Photon Polymerization (2PP) and new specially adapted materials like hybrid polymers (ORMOCERRs). Recent progress in the fabrication of microoptical structures using 2PP and specially designed hybrid polymers is presented. Among the structures are freeform and aberration-optimized microlenses and multilevel diffractive optical elements. These components are discussed with respect to fabrication process and their resulting optical performance. Furthermore, 2PP-initiated refractive index modification, offering high potential for energy-efficient fabrication of 3D optical interconnects, is discussed.
The development of broad area laser diodes towards higher output power, efficiency and brightness is essential to gain progress in almost all laser applications because those devices provide the basis for high power laser sources. To systematically improve the characteristics of high power broad area laser diodes through a design process, it is necessary to have an accurate and efficient computation model self-consistently taking into account optical, electrical and thermal properties. In this publication we present numerical techniques to compute the optical properties of the multimode beam generated by high power AlGaAs broad area laser diodes with an operating wavelength of 970 nm. This simulation considers fluctuations of the carrier and power density as well as the temperature distribution. The numerical results show an excellent agreement to measured data of conventional and microstructured high power broad area lasers. The high computation speed of the model allows optimizing microstructures inside the laser resonator with the use of a genetic optimization algorithm. We show that this design approach potentially leads to a substantial performance gain of the device. In particular degradation of the beam quality due to thermal effects at high injection currents can be controlled.
One of the most common methods to increase the output power of semiconductor waveguide lasers is broadening the
stripe width of the active region. However, this results in higher order transverse modes to be amplified which impairs
the beam quality and increases the beam divergence. By integrating optical elements into the cavity, it is possible to
control the amplitude shape and the number of modes which are amplified in the laser. This paper reports on aspects to
integrate phase and amplitude modifying microstructures into a semiconductor waveguide resonator by adding an
additional lithographic step to the fabrication process of broad area laser diodes. The latest experimental results of such
structured InGaAIP broad area lasers revealed a significant improvement of the beam quality even at a high operation
current. Hence, the expansion of the stripe width of the amplifying region without degrading the beam quality is
possible. The demonstrated power-current characteristics of structured laser diodes exhibit a low threshold current and a
We report on multi-channel detection of ultrashort THz pulses by a linear array of 16 photoconductive dipole antennas.
The dipole antennas built on low-temperature grown GaAs are excited by a line focus of fs-pulses. By the parallel
detection of a complete line of ultrashort THz pulses, the measurement speed of THz ultrashort pulse time domain
systems can be accelerated by an order of magnitude. For demonstration, the THz beam profile along the line detector is
determined, and its spectral dependence of the electric field distribution is compared and verified by wave-optical
An increase in the output power of semiconductor waveguide lasers is commonly achieved through broadening the stripe
width of the active waveguide region. However, the resulting amplification of high order modes may degrade the beam
quality of the laser diode. Further, Filamentation and high peak power densities will limit the lifetime of the device by
optical facet damage. We report an approach to control the slow axis mode behaviour by embedding diffractive phase
structures directly into the waveguide layers of the active laser region. Using this technique it is possible to enhance the
amplification by increasing the overlap with the gain region, whilst additional diffraction losses for higher order modes
are generated. By shaping the zero order mode the output beam quality can be increased and a high efficiency of the
device maintained. Finally we discuss manufacturing techniques of these monolithic waveguide lasers and show how to
integrate phase structures through an additional lithographic step. In our experimental realisation we will demonstrate
that micro structured broad area lasers show a smooth transversal mode shape with significantly reduced current