Alexei Mikhailov

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.