Overview of the shadowgraphic imaging technique and results for various materials

Abstract

Magnified imagery of the focal volume within a nonlinear material, following the arrival of a high power laser pulse, provides insights on the response of the material. Emitted and scattered light images are presented along with time-resolved shadowgraphs (obtained through a pump-probe scheme) showing the response from various limiting materials in both liquid and solid hosts. The different types of images taken together make it possible to determine what occurs and where it occurs within the limiting material. Often unsuspected phenomena are found to be important. Conclusions from the data and the general utility of the technique are discussed.

Solvent effect on the nonlinear absorption of 5,10-A2B2meso substituted porphyrins

“…NLS was 45 previously reported for RSA materials and associated with incomplete dissolution of the material. 15 Evidently herein, the scattered light signal depends on the solvent used. Yet, as previously stated, porphyrin molecules facilitate nucleation of light scattering centers.…”

“…As can be seen from Fig. S2, both the character of the 15 NLA response and the fluence of the final RSA/SA turnover (if detected) varied between solvents and compounds. In order to delineate why this was the case we compared different fitting parameters for all 5,10-A 2 B 2 porphyrins in three solvents: toluene, DMF and chloroform.…”

“…Yet, this phenomenon was considerably enhanced for 15 many porphyrins in chloroform/chlorobenzene and for a number of compounds in chlorobenzene. For these solutions the scattered light signal was detected at low and moderate input energies (40 -100 μJ).…”

“…A low saturation intensity allows the saturated regime of one-photon excited state absorption to be quickly accessed with the input intensity. Analogously, a low saturation intensity allows the saturated regime associated with two-photon excited state absorption to be 15 quickly accessed with the input intensity. However, contrary to , does not always need to be low to maximize OL efficiency, which will be demonstrated below.…”

“…The scattered light signal was measured simultaneously to the detection of the transmitted laser 10 irradiance in the open Z-scan experiments, with the photodetector placed at 30 o angle to the Z-axis. The experimental data obtained for all compounds in toluene, 15 DMF and chloroform at an input energy of ~50 μJ, which corresponds to an onfocus intensity of about 0.6 GW.cm -2 was fitted (where applicable, i.e. for those compounds which exhibited pure RSA response character at the interrogated input energy) with the expression for the normalized transmission 20 versus position along Z-axis to derive effective nonlinear absorption coefficient β eff according to a procedure reported before.…”