Two Methods of Two-Step Excitation Thermal Grating Technique for Detection of Transient Absorption and Stimulated Emission

Abstract

Two different methods for detection of the transient absorption (TA) and stimulated emission (SE) by using a two-step excitation thermal grating technique are characterized. The sensitivity and the temporal profile of the signals are analyzed in detail. One of them, prepulse−(delay)−grating pulse sequence, provides a very sensitive TA detection with a zero background. The other one, grating pulses−(delay)−boosting pulse sequence, has also a very high sensitivity for the detection of TA and SE together with an easy probe wavelength scanning. The high sensitivity of these methods comes from the cyclic excitation of the excited state and accumulation of the thermal energy. These methods are used to measure the T1−T n absorption spectrum of benzophenone, and the T1−T n absorption and SE spectra of rhodamine 6G.

When Is the Helix Conformation Restored after the Reverse Reaction of Phototropin?

“…Recently, Kennis et al 16 reported the direct observation of the photochemical reverse reaction using the transient absorption technique and found that the D state is regenerated on an ultrafast time scale (100 ps) upon photoexcitation of the T state. Using this method combined with a two-step transient grating (TG) method, 17 we measured the refolding dynamics of the linker by initially accumulating the T state by preirradiation with blue light and subsequently photoexciting the T state using a pulsed UV laser (308 nm) to measure the TG signal.…”