Two-photon absorption spectrum

Another interesting example of the effect of non-radiative relaxation on linewidths is visible in the two-photon absorption spectrum of Eu2+ in CaF2 (Downer et al., 1983). These experiments involve the excitation of 4f7 states within the 4f65d band, followed by non-radiative decay to 4T55d states. The excitation was measured by monitoring emission from 41fl5d to 4f7. It is apparent from the spectra that the linewidths of the 4f7 states vary significantly. 

Figure 15-16. (a) Vapor absorption spectrum of tolane at room temperature, (b) Fluorescence excitation spectrum of tolane in a supersonic free jet. The stagnation pressure of He is four atm. (c) Two-photon absorption spectrum of tolane in a supersonic free jet obtained by two-photon resonant four-photon ionization. The stagnation pressure of He is four atm. (Reprinted with permission from Ref. [35].)... 

Cyclohexane Two-photon absorption spectrum of lowest excited singlet state (I A,) of cyclohexane in a supersonic jet. Sharp bands in the region 55 000—58 000 cm assigned to transitions to vibronic levels of 3s, E, Rydberg state. Non-linear Jahn-Teller effects 383... 

As an example of the use of two-photon spectroscopy in assigning excited states that are not observed in one-photon UV spectroscopy, the two-photon absorption spectrum of naphthalene is shown in Figure 1.17. Since for the point group all Bg states have a theoretical polarization degree of H = 3/2, the polarization measurement reveals immediately a Bg state near 42,000 cm . In the two-photon absorption spectrum this shows up only as a shoulder, whereas the maximum at 44,500 cm" can be assigned to an Ag state. Neither state is prominent in the one-photon spectrum. 

Figure 1.17. The two-photon absorption spectrum of naphthalene. The absorption cross section in arbitrary units and the polarization degree fl are shown. For comparison the one-photon absorption spectrum is given by a dotted line (by permission from Dick et al., 1981).

Fig. 3 Trigonal bipyramid Dsh) Fe(CO)5 (a) simulated pure electronic one-photon absorption spectrum CCR(3) excitation energy, CCSD oscillator strength, ANO-3 basis, (b) Simulated pure electronic two-photon absorption spectrum CCR(3) excitation energy, CCSD two-photon cross-section, ANO-3 basis...

Figure 3.66. Two-photon absorption spectrum of 166 in chloroform obtained by upconversion fluorescence measurements using a pumped Nd YAG laser supplying 2.6-ns pulses in the spectral range from 780 to 1120nm with 10-Hz repetition rate. (From Ref. [263] with permission of Elsevier.)...

In considering the single-beam cases, moreover, we have concentrated on the case where A and B differ, even if only by isotopic constitution. However, the theory can also apply to the case where A and B are identical, but the excited states a> and > differ. For a single-component phase, the effect should be observable as the absorption of two photons v/ith energy halfway between that of the two excited states this applies equally to free molecules or loosely associated van der Waals dimers. I or a two-component phase containing a mixture of A and B molecules, il should thus be possible to observe synergistic effects associated with not only A-B, but also A-A and B-B interactions, and hence several new bands should appear in the two-photon absorption spectrum. 

Wang D, Ning L, Xia S, Tanner PA (2003) Theoretical analysis of the two-photon absorption spectrum of Tb " in Cs2NaTbCl6. J Phys Condens Matter 15 2681-2691... 

B.P. Stoicheff, E. Winebergen Doppler-free two-photon absorption spectrum of rubidium. Can. J. Phys. 57, 2143 (1979)... 

Alimpiev et al. 1979) of the MPE spectrum of the SFg molecule, its linear absorption spectrum (bottom), and the theoretical two-photon absorption spectrum (top). As can be seen, the experimentally observed spectrum fits quite satisfactorily the results of a calculation considering only the single- and two-photon transitions to the split... 

Fig. 11.9 Contribution of two-photon transitions to absorption by the lower vibrational levels of the SFe molecule. The linear absorption spectrum of the vibration at low IR radiation intensities is shown at the bottom. When the intensity is raised to 3 x 10 W/cm, there appear in the spectrum (shown in the center), in addition to one-photon peaks, also two-photon absorption peaks (shaded). The theoretical two-photon absorption spectrum is shown at the top. The low-frequency peaks of the Ai and E transitions appear at high radiation intensities, whereas the T2 transition coincides with the linear absorption peak. (Adapted from Alimpiev et al. and Letokhov 1989.)...

Fig. 6.12 Two-photon absorption spectrum of PDA-PTS single crystals (from Ref. 103). The fit is based on the Ag states and parameters in Table 6.6, with 2A magnified in the inset the 1-0 feature has 10% excitation of the ground state (from Ref. 95).

Figure 16. INDO/MRD-CI/SOS simulation of the two-photon absorption spectrum of Th7, as a function of fundamental energy.

In work of some potential import for practical waveguides, Halvorson and Heeger [864] measured the two-photon absorption spectrum of oriented trans-P(Ac)y and found that the two-photon absorption susceptibility ruled out waveguiding devices in this CP. They then cautioned that any CP must be characterized for its two-photon absorption coefficient before attempting to fabricate waveguides from it. 

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