Yuri V. Miklyaev

Novel continuously shaped diffractive optical elements enable high efficiency beam shaping

LIMOs unique production technology is capable to manufacture free form surfaces on monolithic arrays larger than 250 mm with high precision and reproducibility. Different kinds of intensity distributions with best uniformities or customized profiles have been achieved by using LIMOs refractive optical elements. Recently LIMO pushed the limits of this lens production technology and was able to manufacture first diffractive optical elements (DOEs) based on continuous reliefs profile. Beside for the illumination devices in lithography, DOEs find wide use in optical devices for other technological applications, such as optical communications, laser technologies and data processing. Classic lithographic technologies lead to quantized (step-like) profiles of diffractive micro-reliefs, which cause a decrease of DOEs diffractive efficiency. The newest development of LIMOs microlens fabrication technology allows us to make a step from free programmable microlens profiles to diffractive optical elements with high efficiency. Our first results of this approach are demonstrated in this paper. Diffractive beam splitters with continuous profile are fabricated and investigated. The results of profile measurements and intensity distribution of the diffractive beam splitters are given. The comparison between theoretical simulations and experimental results shows very good correlation.

Novel approach for manufacturing of continuously shaped diffractive optical elements

Optical lithography with its 193nm technology is pushed to reach and shift its limits even further. There is strong demand on innovations in illumination part of exposure tools. Current illumination systems consisting of diffractive and refractive optical elements offer numerous benefits such as optimized laser beam shape with high homogeneity and high numerical aperture enabling high efficiency. LIMOs unique production technology is capable to manufacture free form surfaces on monolithic arrays larger than 250mm with high precision and reproducibility. Different kinds of intensity distributions with best uniformities or customized profiles have been achieved by using LIMOs refractive optical elements. Recently LIMO pushed the limits of this lens production technology and was able to manufacture first diffractive optical elements (DOE) based on continuous reliefs profile. Beside for the illumination devices in lithography, DOEs find wide use in optical devices for other technological applications, such as optical communications and data processing. Up to now DOE designs follow the principle of phase diffraction gratings. Its diffraction structure with a periodic phase profile performs a superposition of beams with predefined energy ratios. Due to the application for high precise laser-beam shaping and beam splitting in optical technologies and optical fiber networks, number of grating orders is increased up to some tens or even hundreds. Classic lithographic technologies lead to quantized (step-like) profiles of diffractive micro-reliefs, which causes a decrease of beam splitters diffractive efficiency. The newest development of LIMOs microlens fabrication technology allows us to make a step from free programmable microlens profiles to diffractive optical elements with high efficiency. Our first results of this approach are demonstrated in this paper. Diffractive beam splitters are presented. A special mathematical method is used to design diffractive optical elements with continuous surface profiles. Comparison between theoretical simulations and experimental results shows very good correlation.

Anisotropic transformation of the beam quality of DPSS lasers for shaping of a narrow line focus for laser crystallization of Si

Advanced laser crystallization of Si for flat panel displays demands a narrow line-shaped light focus with an ultimately high homogeneity. Key element of LIMO line shaping system is an anisotropic quality transformation of a multimode laser beam, which permits a very good homogenization for the long axis and tight focusing with a large depth of focus for the perpendicular high-quality axis. A prototype system has been built with a 90-W 532-nm DPSS laser. It provides a 59-mm long and down to 8 μm (FWHM) narrow focus with a residual inhomogeneity of only 1% (rms). The focus width is adjustable and its shape can be tuned from a quasi-Gauss to a top-hat intensity distribution. The depth of focus at 90% of the peak intensity DOF0.9I varies from 120 μm for a line width of 8 μm to 275 μm for FWHM = 14 μm. The design of longer lines is in progress at LIMO.

Asymmetrical M 2 in solid state laser beam shaping for the line scanning laser annealing

A new type of beam shaping system in combination with special characterization of laser parameters provides several mm depth of focus by narrow width and very good homogenization of the line-shaped laser intensity distribution for scanning annealing.

Multistage phased electro-optical planar arrays for the manipulation of high power laser beams

A new type of low-voltage planar electro-optical device for fast beam deflection is reported. It contains two EO modulators, both working as multimode waveguides. The geometry of the waveguides (ratio height to length) enables an efficient self-imaging of the entrance Gaussian mode. The EO modules are from LiNbO3:MgO with the thickness of 32 μm, length 9.75 mm, and width of 26 mm. The second stage works as an active phased array with 16 channels. The design provides a flat wavefront at the exit of the system despite the discrete phase shifts in the array channels. This makes a high steering resolution and optical efficiency possible. The full angle deflection range is of ±32•(1.27λ/D) by using of very low control voltages of 10 - 15 V. The voltages can be further reduced down to 5 V through constructive improvement of the EO-modules. The deflection range can be increased 16 times implementing a 3rd EO stage with a 16- channel EO-array. The deflector provides random access to the available angle states. The access time is limited generally by the capacity of the EO modules. It is of only about 0.1 nF in the reported design. We estimate that thanks to the low control voltage and electrical capacity of EO-modules a switching frequency of about 100 MHz may be possible with an advanced electronics. A relatively large face cross-section of about 1 mm2 will allow using the system with high power lasers and short pulse duration.

Free programmed lens form for the elements of a convex-concave microoptic raster homogenizer

A new type refractive homogenizer provides a 98% light throughput. Special lens form of the microoptic raster elements solves usual problems with interference and diffraction effects even for a small NA.