Formulation of diffraction efficiencies of binary phase gratings for array illumination with ultrashort pulse beams.

We present simple formulas for the diffraction efficiencies of a binary phase grating that performs array illumination with ultrashort pulse beams. Using scalar diffraction theory, we formulated the efficiencies as a function of pulse spectral width by Fourier-transforming the complex-modulated frequency spectra of diffracted pulses in the far-field region. From the analytical simulations, we found that pulse array uniformity departs from unity as the spectral width increases, or the pulse duration decreases, thereby limiting the attainable split counts.

Achromatic optical system with diffractive-refractive hybrid lenses for multifocusing of ultrashort pulse beams.

We report an achromatic cascade optical system for multifocusing ultrashort pulse beams with a diffractive beam splitter. Distortion compensation requires the removal of pulse front distortions from arrayed pulses, which originate from beam-radius-dependent group delay dispersions. The inclusion of hybrid diffractive-refractive lenses can effectively manage system dispersions.

Distortion-compensated multifocusing of ultrashort pulse beams using cascade optical system.

We report a cascade optical system for multifocusing ultrashort pulse beams, particularly sub-50-fs pulses. System achromaticity is key to simultaneous compensation of the spatio-temporal pulse distortions. In this system, diffractive and refractive subsystems are optically coupled in cascade to correct chromatic aberrations, which are the primary cause of pulse distortion.

Design and fabrication of a diffractive beam splitter for dual-wavelength and concurrent irradiation of process points.

We report on a dual-wavelength diffractive beam splitter designed for use in parallel laser processing. This novel optical element generates two beam arrays of different wavelengths and allows their overlap at the process points on a workpiece. To design the deep surface-relief profile of a splitter using a simulated annealing algorithm, we introduce a heuristic but practical scheme to determine the maximum depth and the number of quantization levels.

Subwavelength resist patterning using interference exposure with a deep ultraviolet grating mask: Bragg angle incidence versus normal incidence.

Interference lithography using a deep-ultraviolet (DUV) laser is instrumental in the manufacture of subwavelength patterns used at visible wavelengths. We investigated a grating mask strategy for exposure in terms of how to set and illuminate masks. To obtain high aspect ratio patterns, high fringe visibility, and high exposure uniformity are essential, and for that purpose the use of only two beams with liquid immersion is necessary but not sufficient.

High-efficiency diffractive beam splitters surface-structured on submicrometer scale using deep-UV interference lithography.

We report highly efficient diffractive beam splitters intended for high-power laser applications. Submicron relief structures that work as an antireflective layer are formed on the surfaces of a splitter to improve its transmitted efficiency. Surface structuring is performed using deep-UV interference lithography and reactive ion etching.

Chromatic-distortion compensation in splitting and focusing of femtosecond pulses by use of a pair of diffractive optical elements.

We propose a simple optical system to compensate for chromatic distortion that occurs during fan-out of femtosecond pulses by diffractive optics. The proposed system comprises a pair of diffractive elements, one for splitting an incoming pulse and the other for focusing the split pulses. With an appropriate separation between the elements, chromatic distortion resulting from the spectral bandwidth of a femtosecond pulse is removed, and an array of focused pulses with the same dimensions can be obtained.