Fabrication of Carbon Nanotube Doped Thin Films for Laser Applications.

Abstract: Mode-locked lasers are used for a vast amount of applications, e.g. corneal surgery[1] and optical data storage[2] . The currently established technique for mode-locking with a semiconductor saturable absorber mirror is expensive and in- volves a fairly advanced production technique[3] . Carbon nanotubes incorporated into thin plastic films present an easy to produce and comparatively cheap alter- native. These films are produced by solving carbon nanotubes in a proper solvent, mixing with a host plastic material and finally spin coating to a substrate. Earlier studies have successfully produced and used carbon nanotube thin film saturable absorbers for mode-locking, most notably in the near infrared spectral region[4] . In this work, different solutions are produced using different solvents and varying the carbon nanotube and plastic ratios in these solutions. The different solvents used were toluene, 1,2-dichlorobenzene and acetone. Another fabrication parameter is the revolutions per minute used during the spin-coating process. and the revolutions per minute varied between 500-1250. A total of 17 different solutions was prepared, and spin-coated onto glass substrates with different revolutions per minute. Although proper mode-locking could not be achieved for most of the samples the best solvent seemed to be 1,2-dichlorobenzene which is used in other studies as well[5, 6] . As a result of the laser’s output, which shows modulation, a conclusion of that the sample has non-linear absorber properties can be made. A tendency for q-switching was also observed, however, this operation is unstable in terms of repeti- tion rate. To be able to get desired laser behavior the modulation introduced by the absorber has to be adjusted, by altering e.g., the film’s thickness or carbon nanotube concentration. No proper mode-locking was observed for toluene regardless of the concentration of solvent or carbon nanotubes.