We have demonstrated the directional control of surface plasmon polariton(SPP) waves through propagating in an
asymmetric plasmonic Bragg resonator using femtosecond temporal-phase control via the resonant coupling of SPPs and
the interference of SPPs. The near-field images display significant temporal-phase dependence, switching between left
and right propagation after the Bragg resonator.
Ultrafast lasers have many applications mainly due to its two properties, the ultrashort pulse width and the ultrahigh intensity. Because the former is the main cause of the latter, it is very important to exactly measure the pulse width of the ultrafast laser. Currently, there are several different kinds of experimental methods to measure the ultrashort pulse width. Among those systems for this measurement, the autocorrelator using the second harmonic generation (SHG) is by far the most simple and basic method. This type of autocorrelators usually uses inorganic crystals, such as BBO, as the SHG medium. The thinner medium is necessary for analyzing the shorter laser pulses. However, the polishing process which is necessary for obtaining the optically good surfaces makes it difficult to reduce the thickness of medium as desired. We present an autocorrelator system which overcomes these shortcomings. Our system is based on the SHG using organic polymer. Polymers can be easily prepared in the form of thin film on the strong substrate through the process of spin casting. Thickness less than 1 m can be obtained without difficulties. Furthermore, due to its high nonlinearity, thin film of polymer can produce the bright second harmonic light. Polyurea was used as the second harmonic generation material of the autocorrelator because it has the pretty good transparency. An autocorrelator system based on the 397nm-thick poled polyurea thin film has been developed and used to measure the pulse width of a home-made Ti:sapphire laser oscillator. Then, the system was compared with that based on a 100 μm-thick BBO crystal, which is widely used. The pulse width of laser beam was measured to be 9.8 fs with the former. The value is believed to be more accurate than that of 7.2 fs measured with the latter.
The third-order nonlinear optical properties of a methyl substituted Texaphyrin, [(CH3-TXP)Cd]Cl, were studied by degenerate four wave mixing and Z-scan techniques using 40 ps laser pulses at 532 nm. The molecular second- order hyperpolarizability ((gamma) ), the excited-state absorption cross section ((sigma) ex), the nonlinear refractive cross section ((sigma) t), and the optical limiting performances at both nanosecond and picosecond time scales have been determined. We have also studied the third- order nonlinearity of SiNc, one of the most promising optical limiting materials in literature, for comparison. The (gamma) value for [(CH3-TXP)Cd]Cl is 6.9 X 10-31 esu, which is 4 times as larger as that of SiNc. The nonlinearity of [(CH3-TXP)Cd]Cl is predominantly electronic in origin with picosecond laser pulses. The excited-state absorption cross section ((sigma) ex) and the nonlinear refractive cross section ((sigma) t) obtained from the theoretical simulation and calculation of Z-scan results are 7.0 X 10-17 cm2 and 1.7 X 10-17 cm2, respectively. The complex shows strong optical limiting performance via reverse saturable absorption for 5 ns laser pulses. The nonlinear absorption of this molecule for 40 ps laser pulses exhibits a transition from reverse saturable absorption to saturable absorption when the fluence is higher than 0.3 J/cm2. These data suggest that this complex and related complexes are a promising class of nonlinear optical materials.
Detailed degenerate four wave mixing (DFWM) studies of one molybdenum complex, cis-Mo(CO)4(PPh3)2 in dichloromethane (CH2Cl2) and tetrahydrofuran (THF) are reported in this paper. Upon exposure to air/oxygen, the (chi) (3) values of CH2Cl2 and THF solutions of this complex increase dramatically with time. However, when excess free ligand is added to CH2Cl2 solution of the complex, the increase in (chi) (3) value is stopped. Hence, it is possible to obtain a CH2Cl2 solution with high (chi) (3) value by first oxidizing the solution and then adding excess ligand to stabilize the solution. For THF solution, probably due to the different mechanism causing the increase of (chi) (3) values, the increase in (chi) (3) values doesn't stop even though excess free ligand is added. Further, the increase in the (chi) (3) values of both the CH2Cl2 and THF solutions parallels the increase in the linear absorption but it is unclear whether the increased linear absorption plays any role in the increase in the (chi) (3) value of the solution. This study also shows how degenerate four wave mixing can be used as a very sensitive technique to detect the chemical change in a solution when the third order optical nonlinearities of the reactant and product are very different.
The optical limiting performances of nine asymmetric pentaazadentate porphyrin-like metal complexes {[(R- APPC)M]Cln} have been measured at 532 nm with nanosecond pulses. In a fl38 geometry, with sample transmission of 0.51 approximately 0.80 in a 2 mm cell, the limiting thresholds for these complexes were 1.4 approximately 150.0 mJ/cm2. The throughputs of these complexes were limited to 0.31 approximately 1.42 J/cm2 for incident fluences as high as 3.5 J/cm2. The limiting throughput was strongly influenced by the nature of the ligand and metal ions. Lower bounds for the ratio of triplet excited-state to ground state absorption cross sections have been estimated at 2.3 approximately 5.7. The lower limiting thresholds, lower limiting throughputs, as well as the ease of modification of the ligands and variation of the metal ions, make these complexes promising candidates for optical power limiters.
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