104 nm period grating fabrication in fused silica by immersion two-beam interferometric laser induced backside wet etching technique

A substantial extension of the method of two-beam interferometric laser induced backside wet etching (TWIN-LIBWE), the immersion TWIN-LIBWE, is used to fabricate fused silica gratings with a 104 nm period. The spatially filtered fourth harmonic of Nd:YAG laser (lambda=266 nm, tau(FWHM)=8 ns) pulses were split into two parts which then interfered at the backside of the fused silica target in contact with a liquid absorber (naphthalene methyl methacrylate saturated solution with a concentration of 1.85 mol/dm(3)). The hypotenuse of a rectangular fused silica prism is attached to the fused silica target with the use of distilled water as the immersion liquid. On steering the beams through the sides of the prisms, the angle between the two laser beams has been substantially increased. The resulting period of 104 nm is the minimal grating constant achievable under such experimental conditions and, to our knowledge, the smallest laser generated grating period in fused silica at present.