Laser interference

Mattheyses, A. L., Shaw, K. and Axelrod, D. (2006). Effective elimination of laser interference fringing in fluorescence microscopy by spinning azimuthal incidence angle. Microsc. Res. Tech. 69, 642-7. 

Matsuo S, Kondo T, Juodkazis S, Mizeikis V, Misawa H (2002) Fabrication of three-dimensional photonic crystals by femtosecond laser interference. In Adibi A, Scherer A, Lin S-Y (eds) Photonic bandgap materials and devices. SPIE Proc 4655 327-334... 

All lasers in current use for analytical Raman spectroscopy must be filtered to reduce laser interferences. A perfect filter would exhibit 100 per cent transmission of the laser line, while totally blocking all other light a few reciprocal centimeters away from the laser. In reality, several different types of filters are used for Raman, which approximate ideal performance to varying degrees. Of interest here are interference filters and premonochromators. 

This article addresses key aspects of diffractive optics. Common analytical models are described and their main results summarized. Exact numerical methods are applied when precise characterization of the periodic component is required, whereas approximate models provide analytical results that are valuable for preliminary design and improved physical insight. Numerous examples of the applications of diffractive optical components are presented. These are optical interconnects, diffractive lenses, and subwavelength elements including antireflection surfaces, polarization devices, distributed-index components, and resonant filters. Finally, recording of gratings by laser interference is presented and an example fabrication process summarized. 

Two-wave laser interference (Fig. 20(a)) may be used to record periodic elements with subwavelength features (A 100 nm). The UV laser (for example helium cadmium, argon-ion, or excimer laser) beam is focused down with an objective lens and passed through a matching pinhole to spatially filter the beam. The central part of the emerging spherical wave, which has nearly planar phase fronts, illuminates the sample directly. A part of the wave is reflected towards the sample as shown. These two waves interfere to produce a standing, periodic intensity pattern with period... 

FIGURE 20 (a) Laser interference grating recording system, (b) Details of interference light pattern. 

Laser-interference exposure development Hard bake at 1 lO C for 20 minutes Reactive-ion etch (RIE) photoresist (ashing)... 

Although modern computers calculate such spectra in fractions of a second, they can give high resolution only if the moving mirror is positioned exactly by using laser interference (A,r 1/AA). 

Direct Laser Interference Micro-Nanopatteming (DLIP) has been used to build nanometer sized PANI arrays (as thin as 600 nm) self-assembled on dielectric polymers the width of the polymer lines can be modulated by changing the laser beam intensity, without loss of the chemical and electronic properties of PANI. It is interesting that the dielectric substrate can be ablated, exploiting its optical properties at the working wavelength. The authors believe this technique relevant for the development of polymer based sensors [170]. 

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