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Transient hole burning in the oligomer region of the OH-stretching mode of ethanol dissolved in carbon tetrachloride is demonstrated, using two-color IR spectroscopy with excitation and probing pulses of 2 and 1 ps, respectively. The observed inhomogeneous broadening of the oligomer band is explained via local disorder of the hydrogen bonds. The lifetime of the spectral holes is estimated to be approximately 1 ps, providing evidence for rapid spectral relaxation and/or migration of vibrational excitation. The observed time evolution of excited state absorption from v = 1 to v = 2 levels yields the v = 1 population lifetime of 1.4 ± 0.3 ps. Breaking of the ethanol rings or chains as indicated by longer-lived induced absorption in the dimer/trimer region around 3450 cm-1 and further spectral features are reported.

Transferal and recursive filter coucepts, normally associated with diserete-time applications, are adapted for implementation in the microwave frequency range. Principal focns is on microwave active filter designs that permit realization of wide bandwidths, with microwave transistors used as active elements. A transversal-type and a recursive-type experimental filter, both of which exhibit 9-15-GHz bandpass responses, serve to illustrate aspects of physical implementation, while offering a convenient basis for comparing the two different approaches. I.

Transient spectral hole burning and hydrogen-bond breaking determined in different solutions of ethanol in deuterated ethanol

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We report on the observation of two-photon absorption for the direct gap in intrinsic germanium at room temperature using two independently tunable picosecond, mid-infrared light pulses. The two-photon absorption coefficient is determined for different wavelengths, and carrier densities down to about 1013 cm−3 could be detected at a sample length of 700 μm. Two-photon absorption in germanium is demonstrated to be a versatile tool for zero-point determination in time resolved pump-probe investigations and permits a precise measure of the time resolution of the laser system.

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We propose a detailed structural model for ethanol oligomers assuming it to form open chains. An inhomogeneous broadening with a width of about 100 cm−1 of the OH-stretching mode of the hydrogen-bonded species is considered, a parabolic increase of the absorption strength and a cubic dependency of the frequency of this vibration with position within the associate. With these asumptions we are able to account for the measured conventional IR absorption spectra of ethanol at different dilutions in CCl4 with the most probable length of the associates ranging between 2 and 13 molecules, respectively. Application of our model to time-resolved spectroscopy on a 0.17 M sample with excitation performed at 3340 cm−1 yields a length of the excited oligomers of 4 to 5 and of broken species of 2 to 3, respectively.