Growth and optical properties of copper selenide nanowires (nws) in alumina template were studied and discussed in respect to their application as films doped with semiconductor nanocrystals that provide promising optical properties. The results obtained indicate that nanoscaled copper selenide structures uniformly embedded at the bottom of alumina less than a micron in depth could be useful for mode locking in picosecond YAG type lasers. The operating wavelength of the material was identified by optical characterization. Copper selenide nanowires were examined as saturable absorber to yield passive wave mode-locking in a Nd 3+ / YAG laser (λ = 1.064 µm). Both the deposition conditions and subsequent annealing define the stoichiometry of copper selenides providing a slight shift of absorption spectra. One of the preponderant modern sciences nowadays is nanotechnology. While studying new semiconductor nanomaterials, great interest arrived for copper selenide nanoparticles [1][2][3][4][5][6][7][8][9]. One of their promising applications is optical switching devices, because of the transient bleaching effect [7][8][9]. Size, chemical composition, and crystalline structure of nanoparticles determine the character of light absorption processessame as for indirect p-type semiconductor, copper selenide Cu x Se y . Under ambient conditions the material exists as a series of stable and metastable phases, with the stoichiometry coefficients x and y varying from 1 to 3. Variation in stoichiometry results in change of crystalline structure, absorption spectra, and both direct and indirect band gap E g,dir , E g,indir values [10]. Moreover, the crystalline structure and phase composition of copper selenide leads to different optical and other properties obtainable by annealing of specimens.In recent years, a number of researchers have explored semiconductor nanocrystals as saturable absorbers to create passive mode-locked solid-state lasers [7][8][9]. Nanostructured copper selenide appears to gain shallow absorption centres characterized by the absorp- * The report presented at the 37th Lithuanian National Physics Conference, 11-13 June 2007, Vilnius, Lithuania.tion peak in near-IR, which leads to optical nonlinearity effects [10]. The observed absorption range appears to be consistent with the first harmonic of YAG type solid state laser (wavelength within 1-1.5 µm). We studied here for the first time the nonlinear optical properties and mode-locking performance of porous alumina thin films containing copper selenide. Thus, arrays of nanoscaled Cu 3 Se 2 (umangite) before and after annealing at several different temperatures were fabricated and investigated.Aluminium foil of 100 µm in thickness and 99.995 at% purity from Goodfellow was used to prepare samples of 12 × 12.5 mm 2 in dimensions. Before anodizing, the surface of samples was cleaned by degreasing in acetone, etching in a hot 1.5 M NaOH solution for 20 s, desmutting in 10% HNO 3 , thoroughly rinsing, and drying in nitrogen stream. The growth of porous aluminium ox...