Nonlinear optical properties of chalcogenide glasses

Two different nonlinear optical effects were investigated in chalcogenide glass and glass fibers for their potential to produce light sources in the near-, mid-, and far-infrared spectral regions. Raman amplification in small core As39Se61 fiber was demonstrated. Over 20 dB of gain was observed in a 1.1 meter length of fiber pumped by a nanosecond pulse of ∼10.8 W peak power at 1.50 mum. The peak of the Raman gain occurred at a shift of ∼230 cm-1. The Raman gain coefficient is estimated to be about 2.3 x 10-11 m/W, over 300 times greater than that of silica at the same wavelength. The large Raman gain coefficient coupled with the large IR transparency window of these fibers shows promise for development of As39Se61 Raman fiber lasers and amplifiers in the near-, mid- and far-IR spectral regions. A computer model using a finite element technique was written to model the behavior of such a laser. The model demonstrates the feasibility of a middle infrared fiber Raman laser pumped at 5.59 mum by a carbon monoxide laser and operating at a wavelength of 6.46 mum. This wavelength may be of interest in surgical applications. Calculations show slope efficiencies can approach 80% with moderate threshold powers. Measurements of the nonlinear indices of refraction at 1250 nm and 1550 nm for a set of chalcogenide glasses were presented and compared to theoretical models. The measurements show that As40Se60 has the highest nonlinear index, over 1000 times that of silica at a wavelength of 1250 nm. The models predict that in the mid-IR these glasses will still have nonlinear indices two-orders of magnitude greater than silica in the near-IR. Exploiting the large nonlinearity of these glasses to produce super continua in the mid-IR was investigated. The group velocity dispersion (GVD) of As40S60 and As40Se 60 was calculated based on index dispersion data. The minimum GVD was determined to be at 3.0 mum and 6.3 mum for As40S60 and As40Se60, respectively. Femtosecond laser pulses at a wavelength of 2.5 mum were launched into As40S60 and As40Se60 fiber. Significant spectral broadening was observed in both fibers.