In this work, the photodegradation of a polymer optical fiber with Rhodamine doped cladding as a function of illumination time and excitation intensity is presented. To show the effect of photodegradation on different bulk geometries and environments, the photodegradation from a dye doped preform and a PMMA thick film is also evaluated. The reversible and the irreversible degradation of the florescent material were quantified under an established excitation scheme. To this purpose, a four-level system to model the photodegradation rates and its relation with the population of the states is presented and it is used to justify a possible underlying mechanism. The obtained results suggest an increase of one order of magnitude in the stability (lifetime) of the polymer optical fiber with respect to the preform or the thick film geometry stability.
Photoluminescence as a function of time, wavelength and temperature is used to elucidate the relaxation of energy in PbSe as a function of the structural arrangement of the nanocrystals. The contribution of radiation emission, Förster exchange and nonradiative relaxation are accounted in processes from 77 to 300 K and in the wavelength from 1.65 to 1.20 um and in temporal scales from 1 ns to 10 us. Important contribution to the nonradiative relaxation with the mesoscopic arrangement of the nanocrystals and evidence of the Föster exchange independent of temperature and around 25 ns is measured. The general description of relaxation is used as well to correlate with the complex interaction between nanocrystals.
An optical fiber deformed as a micropipette is employed to force the evanescent wave to interact with its environment. The multimode fiber is removed of its cladding and with a combination of heat and tension a reduction in the diameter is achieved to force the evanescent wave to increase its power. A dispersive analysis of the radiation transmitted between 400 nm and 2000 nm is measured and compared with simulation on a similar geometry.
The transmission matrices are associated with the paraxial theory, usually assumed as rough approximation useful in non critical applications. The generalized Kosterbauder matrices of transmission are helping to develop a framework to analyze and to design optical systems, particularly systems where the phase description is important as in femtosecond and shorter pulses propagation. Here the primitive generalized matrices for each interface is presented and applied to analyze simple optical systems to describe its behavior, particularly the group velocity dispersion.
Operation of Cr:LiSAF laser pumped by 670 nm high brightness single stripe (width of 50 μm) laser diode with pump-threshold as low as 650 μw is reported. The lasing threshold was observed simultaneously with threshold of operation of laser diode. For short pulse generation we designed and tested different multiple quantum well saturable absorbers. The continuous mode-locked operation was achieved with tunability from 846 to 875 nm.
Operation of laser diode pumped Cr:LiSAF laser in 1 m long V-resonator with pump-threshold as low as 650 uW is reported. This threshold was observed simultaneously with threshold of single stripe (width of 50 um) 670 nm laser diode used as a pumping source.
We present a technique for the absolute measurement of very low-level scattering. The method is absolute in that it relies on fundamental physics and does not require calibration against standards maintained by the National Institute of Standards. In a bi-directional mode-locked ring laser, a difference in longitudinal mode frequency between the two senses of circulation of the intracavity pulses can be measured as a beat note between the corresponding outputs. A very small amount of light backscattered by a sample (located at the pulse crossing) from one sense of circulation into the other, causes the beat note to vanish. The threshold in mode frequency difference that causes locking is a measure of the scattering amplitude.
We have used the z-scan technique to determine the sign and magnitude of the off-resonant n2 and two photon absorption coefficient of PTS-polydiacetylene. The sign of n2 is negative and the magnitudes of nonlinearities are consistent with our previous reports on waveguide measurements.