Echelles vs. lamellar ridge gratings for lline narrowing of DUV excimer lasers

Echelles are often used as external resonator cavity diffraction grating in Littrow mount. Because of its high angular dispersion it is the main component for narrowing the laser line of high power excimer lasers for DUV lithographic applications. Recent research improved the grating efficiency of coated echelles to 70-80% which is maximum in the DUV spectral range [1]. Rigorous theoretical investigations show that lamellar ridge gratings can even reach 90% efficiency. We present recent results for coated echelles and discuss the advantages and disadvantages of echelles and ridge gratings in the mentioned DUV line narrowing application. [1] B.H. Kleemann, J. Erxmeyer, 2004, Independent electromagnetic optimization of the two coating thicknesses of a dielectric layer on the facets of an echelle grating in Littrow mount, J. mod. Opt. (51), 2093-2110.