Excited-State Absorption in ns to fs time resolution

Optical transmission of a sample of solved organic molecules in general, is changed by excitation by laser pulses of high intensity. By this, a second light beam can be influenced, an effect that e.g. can be used for optical switching. In addition new absorptions occur which with their fast relaxation times in the ps- and ns-range are particularly interesting for the construction of opto-optical switches. They can be investigated by time resolved spectroscopy. For this reason intensity dependent transmission and transient absorption after excitation by short laser pulses are measured. Laser pulses of ns, ps and fs duration are produced to investigate the temporal behavior of a sample from the second to the femtosecond range. Excited State Absorption (ESA): Here, the sample to be investigated is excited by laser light of the intensity Ipump. The excited state is probed by a second light pulse of Iprobe. Example: Development of the transient spectra of 4-n-pentyl-4-cyanobiphenyl after excitation by 308 nm.