Phase mask

The driving fields in nonlinear coherent microscopy can be dressed with alternative phase profiles. One of the simplest phase masks is a one-dimensional r-phase step across the transverse Gaussian beam profile. The resulting phase pattern resembles... 

Simulations of the experimental signal were performed using Equation 1 without adjustable parameters. The spectrum of the pulse and the absorption spectrum of HPTS were measured experimentally. An examination of the molecular structure of HPTS shows that it has no center of symmetry. Since parity restrictions may be relaxed in this case, the similarity between one-photon and two-photon absorption spectra is expected. The spectral phase

theoretical data were normalized such that the signal intensity is unity and the background observed is zero. The experimental data (dots) generally agree with the calculated response (continuous line) of the dyes in all pH environments (see Fig. 2). 

The development of phase masks using the refractive index variation due to the UV-photodecomposition of the polysilane was examined.134 The refractive index due to UV-photodecomposition of PMPS changes from 1.70 to 1.56. The refractive index variation in PMPS films by UV-light irradiation is shown in Figure 31. 

Figure 3. Binary phase masks of equilibrium VGO catalyst images. a) particle location mask b) Si/Al intensity ratio c) high Si/Al ratio mask d) high lanthanum mask e) zeolite mask (logical AND of c d)...

The amplitude and phase corrections are calculated from the target pulse and the acquired pulse using a TADPOLE measurement, and the new amplitude and phase mask functions are simultaneously rewritten to the pulse shaper. The difference between the measured phase and the target... 

Rogers, J. A., et al. (1997), Using an elastomeric phase mask for sub-100 nm photolithography in the optical near field, Appl. Phys. Lett., 70, 2658-2660. 

In order to produce surface-relief electro-optic gratings, Munakata et compared two fabrication methods of SRG inscription. In the first, the SRG was produced with an interference pattern of cw laser, with relatively modest intensities. The gratings so recorded were photo- and thermally erasable, and efficient writing was polarization dependent. In the second method, a phase mask was employed to provide the periodic intensity modulation of a pulsed laser, the 3rd-order harmonic (at 355 nm) of a Nd YAG laser. The SRG was produced with a single laser pulse, allowing a very short fabrication time (less than Is). The direshold for ablation was 500 mj/(em pulse), and the amplitude of the SRG increased with pulse energy. A depth of up to 300 rim could be achieved, leading to a smooth but not sinusoidal surface modulation. 

FIG. 14.24 Experimental setup employed For direct photoprintlng from a phase mask. 

Li, Z.-Y, Yin, Y, and Xia, Y, Optimization of elastomeric phase masks for near-field photolithography, Appl. Phys. Lett, 78, 2431, 2001. 

The combination of gray-tone phase masks with the highly sensitive photopolymers is suitable for the fast fabrication of three-dimensional topographies. Single laser pulses can create complex structures, such as Fresnel lenses. A pattern transfer into glass or quartz, e.g., by proportional etching techniques, would open an even larger spectrum of applications. 

The combination of phase masks and specially designed, highly sensitive photopolymers can be used to fabricate fast, three-dimensional topographies using laser ablation. The improvements of the phase mask, by incorporating the ablation behavior of the polymer into the mask design, and the application of photopolymers which decompose without contamination of the surface, allows a fast fabrication of microoptical elements. 

J. A. Rogers et al.. Generating approx. 90 nm features using near-field contact-mode photolithography with an elastomeric phase mask, J. Vac. Sci. TechnoL, B, 16, 59, 1998. 

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