Time resolved photoacoustic spectroscopy applied to properties of picosecond transients

Abstract

Time resolved photoacoustic spectroscopy represents a promising new approach to the study of time resolved absorption with picosecond time resolution. The sensitivity of photoacoustic detection permits investigation of dilute and fluorescent samples which are difficult to study by conventional flash photolysis. Theory shows that quantitative measurements of important transient properties and new insights into photochemical and photophysical dynamics can be obtained by measuring heat deposition as a function of probe fluence. Experimental determinations of absorption and stimulated emission cross sections, and lower limits for rates of nonradiative relaxation of highly excited states, are presented.

Investigation of the Excited-State Dynamics of Radical Ions in the Condensed Phase Using the Picosecond Transient Grating Technique

“…This technique can be considered as flash photolysis with calorimetric detection . The advantage of monitoring the density grating instead of using a photoacoustic detector is that the heat generated by P 4 and P 5 does not contribute to the signal. , Figure b shows the diffracted intensity measured with the AQ/DABCO pair as a function of the time delay between P 5 and the grating pulses, P 1,2 . When the latter pulses arrive on the sample before P 5 , the absorbance at 532 nm is the highest and the amplitude of the density grating is the highest as well.…”

Time-resolved photothermal and photoacoustic methods applied to photoinduced processes in solution

“…The conclusion was that the oxygen impurities which are associated with the latter centers and greatly increase their stability do not significantly quench their fluorescence.135 of the stilbenes, and the stimulated emission cross sections of benzophenone and coumarin 485. 71 By varying the time delay between two picosecond pulses, the measurement of a fast relaxation process is principally limited by the uncertainty in the delay between pulses and by the pulse width. Heritier and Siegman72 found the excited-state cross section of rhodamine 6G not to be in agreement with that found by Star-obogatov136 or Penzkofer and Wiedmann.…”

Magnification in Excess of 100-Times of the Microscopic Photothermal Lensing Signal from Solute Molecules by Two-Color Excitation with Continuous-Wave Lasers

“…Heat generation via transient absorption has been observed and applied to investigate the dynamics of molecules in dilute solution, where sequential pulsed excitation was used in combination with photothermal detection. [12][13][14][15] Fortunately, a high efficiency of photon energy conversion into heat is expected for the transient absorption of visible light, because the highly photoexcited molecules in liquid generally relax with a small yield of photon emission, extremely rapidly to vibrationally and electronically lower excited states unless the photon energy is high enough to cause the molecules to ionize or dissociate into fragments.…”