We present the details of an experimental observation of excited-state enhancement of the degenerate-four-wave-mixing (DFWM) susceptibility γₙS(-{ω};{ω},{ω},-{ω}) of a conjugated linear chain, diphenylexatriene (DPH), when the first {π}-electron excited state is populated for nanosecond time scales and then probed nonresonantly through picosecond DFWM. An increase as large as a factor of 100 in the completely nonresonant 1064-nm DFWM signal from the highest DPH concentrations (8 mM) is observed when the 355-nm pump beam saturates the S₂ absorption as compared to when the pump beam is turned off. A large γ₂S(-{ω};{ω},{ω},-{ω}) of (12 000±{}1700)×{}10^-36 esu is found, compared to the ground state γ₀S(-{ω};{ω},{ω},-{ω}) which is 50×{}10^-36 esu. Importantly, separate transient absorption experiments show that there is no excited-state absorption at 1064 nm with excitation at 355 nm. Therefore, upon population of the excited state, the electronic third-order optical susceptibility of DPH is increased by orders of magnitude, without introducing any optical loss at the probe wavelength.
No takes yet. Share an insight, caveat, or question.
Rodenberger et al. (1995) studied this question.