EFFECT OF LASER PROCESSING PARAMETERS ON SPECTRAL CHARACTERISTICS OF SILVER-IMPREGNATED TITANIUM DIOXIDE THIN FILMS

Subject of Research. Local and precise control of nanocomposite material optical properties become possible due to lasers. Laser irradiation can be used as an instrument for the fabrication and modification of such materials. However, for practical applications, it is necessary to know how laser processing parameters impact on spectral characteristics of composite materials which, as a rule, are related to sizes and distribution of nanoparticles. The paper presents research results of the laser processing parameters impact on the reflection spectra of nanocomposite material based on titanium dioxide. Methods. Sol-gel titanium dioxide thin films impregnated with small (less than 5–7 nm) silver nanoparticles on glass slides were exposed to a 405 nm ultraviolet laser. Changes in the sample reflection spectra after laser processing in the continuous wave mode were studied via optical spectrophotometry in the range of 350–760 nm. Main Results. An array of laser tracks on the sample surface was recorded with such processing parameters as the scanning speed and average radiation power. Each track had central and edge areas which were visually observed. Experimental data analysis showed that there was a shift in the reflection spectra peak position in these two areas in the range of 380–440 nm. In order to determine the reasons for such spectral changes, numerical modeling was carried out using the effective medium model in the Bruggemann-Bergman approximation. It was found that the size and distribution of silver nanoparticles at the edges and in the center of the laser processed area may vary. The scanning speeding-up and the average radiation power decrease leads to an increase of nanoparticles size. These size changes occur due to various temperature distributions. Practical Relevance. Control methods for spectral characteristics of sol-gel silver-impregnated titanium dioxide thin films via local laser resizing of nanoparticles are demonstrated. The obtained results are promising for a number of applications: integrated optics, photonics devices, biosensors, photocatalytic devices, and security labels.