Concept and optical design of a compact cross-grating spectrometer.

The concept of a new compact echelle-inspired cross-grating spectrometer is introduced, and a specific optical design is presented. The new concept aims to achieve simultaneously a high spectral resolution, a wide accessible spectral range, and compact dimensions. The essential system novelty concerns the combination of different aspects: the implementation of a crossed grating comprising both the main dispersion and order separation, a folded reflective beam path, which enables a reduction of the system volume, and the introduction of a form-adjustable mirror for aberration compensation. The exemplary optical design offers a spectral bandwidth ranging from 330-1100 nm with spectral resolution better than 1.4 nm in the fourth and 0.4 nm in the 11th order. The optical setup covers a volume of 110 mm×110 mm×30 mm.

Compact echelle spectrometer employing a cross-grating.

The concept and the implementation of a compact and simplified echelle spectrometer are presented, and the working principle is demonstrated by first experimental measurements. The crucial element of the setup is a cross-grating, combining an echelle grating utilizing several higher diffraction orders (5th up to 11th) and a superposed perpendicular-oriented cross-dispersing grating. Two alternative manufacturing approaches for the cross-grating are presented and discussed. The first approach combines Talbot lithography for the deep echelle grating and interference lithography for the cross-dispersing structure. As a second approach, direct laser-beam writing was applied. The compact echelle spectrometer covers a spectral range from 380 to 700 nm and offers a spectral resolution of ∼2 nm.

Influence of oblique illumination on perfect Talbot imaging and nearly perfect self-imaging for gratings beyond five diffraction orders.

The Talbot self-imaging effect of amplitude gratings is afflicted with aberrations that distort the self-image. This occurs especially if the grating period p is only a few times larger than the illumination wavelength λ. For example, for lithographic applications of the Talbot effect these aberrations lower the lateral writing resolution and should be minimized. Noponen found, however, some discrete ratios of p/λ in the interval of 2.0

Quantitative analysis of imperfect frequency multiplying in fractional Talbot planes and its effect on high-frequency-grating lithography.

Fractional Talbot images of amplitude line gratings, with small opening slits compared to the period, are characterized by an integer multiple of the gratings' spatial frequency. We investigate the formation of fractional Talbot images analytically within a scalar framework and give a comprehensible insight into the paraxial limits involved. Particular attention is paid to nonparaxial effects on the intensity distribution at fractional Talbot planes and their lateral periodicities. We present a comparison between the measured intensity distributions and a numerical implementation of our analytical method. Both ways reveal the paraxial limits of frequency multiplication on fractional Talbot images. The use of fractional Talbot images for lithography results in ghost diffraction orders. We roughly estimate the ghost orders quantitatively with a simple numerical model for monochromatic and polychromatic illumination.

Flexible mask illumination setup for serial multipatterning in Talbot lithography.

A flexible illumination system for Talbot lithography is presented, in which the Talbot mask is illuminated by discrete but variable incidence angles. Changing the illumination angle stepwise in combination with different exposure doses for different angles offers the possibility to generate periodic continuous surface relief structures. To demonstrate the capability of this approach, two exemplary micro-optical structures were manufactured. The first example is a blazed grating with a stepsize of 1.5 µm. The second element is a specific beam splitter with parabolic-shaped grating grooves. The quality of the manufacturing process is evaluated on the basis of the optical performance of the resulting micro-optical elements.