9 research outputs found
Mode spectrum and temporal soliton formation in optical microresonators
The formation of temporal dissipative solitons in optical microresonators
enables compact, high repetition rate sources of ultra-short pulses as well as
low noise, broadband optical frequency combs with smooth spectral envelopes.
Here we study the influence of the resonator mode spectrum on temporal soliton
formation. Using frequency comb assisted diode laser spectroscopy, the measured
mode structure of crystalline MgF2 resonators are correlated with temporal
soliton formation. While an overal general anomalous dispersion is required, it
is found that higher order dispersion can be tolerated as long as it does not
dominate the resonator's mode structure. Mode coupling induced avoided
crossings in the resonator mode spectrum are found to prevent soliton
formation, when affecting resonator modes close to the pump laser. The
experimental observations are in excellent agreement with numerical simulations
based on the nonlinear coupled mode equations, which reveal the rich interplay
of mode crossings and soliton formation
Efficient visible luminescence of nanocrystalline silicon prepared from amorphous silicon films by thermal annealing and stain etching
Films of nanocrystalline silicon (nc-Si) were prepared from hydrogenated amorphous silicon (a-Si:H) by using rapid thermal annealing. The formed nc-Si films were subjected to stain etching in hydrofluoric acid solutions in order to passivate surfaces of nc-Si. The optical reflectance spectroscopy revealed the nc-Si formation as well as the high optical quality of the formed films. The Raman scattering spectroscopy was used to estimate the mean size and volume fraction of nc-Si in the annealed films, which were about 4 to 8 nm and 44 to 90%, respectively, depending on the annealing regime. In contrast to as-deposited a-Si:H films, the nc-Si films after stain etching exhibited efficient photoluminescence in the spectral range of 600 to 950 nm at room temperature. The photoluminescence intensity and lifetimes of the stain etched nc-Si films were similar to those for conventional porous Si formed by electrochemical etching. The obtained results indicate new possibilities to prepare luminescent thin films for Si-based optoelectronics