Time-resolved multiphoton

P.E. Morton, T.C. Ng, S.A. Roberts, B. Vojnovic, S.M. Ameer-Beg, Time resolved multiphoton imaging of the interaction between the PKC and NFkB signalling pathways, Proc. SPIE 5139, 216-222 (2003)... 

In this chapter we describe advances in the femtosecond time-resolved multiphoton photoemission spectroscopy (TR-MPP) as a method for probing electronic structure and ultrafast interfacial charge transfer dynamics of adsorbate-covered solid surfaces. The focus is on surface science-based approaches that combine ultrafast optical pump probe excitation to induce nonlinear multi-photon photoemission (MPP) from clean or adsorbate covered single crystal surfaces. The photoemitted electrons transmit spectroscopic and dynamical information, which is captured by their energy analysis in real or reciprocal space. We examine how photoelectron spectroscopy and microscopy yield information on the unoccupied molecular structure, electron transfer and relaxation processes, light induced chemical and physical transformations and the evolution of coherent single particle and collective excitations at solid surfaces. 

Volkmer, A., Hatrick, D. A. and Birch, D. J. S. (1997). Time-resolved nonlinear fluorescence spectroscopy using femtosecond multiphoton excitation and single-photon timing detection. Meas. Sci. Technol. 8, 1339 19. 

Nanosecond Absorption Spectroscopy Absorption apparatus, 226, 131 apparatus, 226, 152 detectors, 226, 126 detector systems, 226, 125 excitation source, 226, 121 global analysis, 226, 146, 155 heme proteins, 226, 142 kinetic applications, 226, 134 monochromators/spectrographs, 226, 125 multiphoton effects, 226, 141 nanosecond time-resolved recombination, 226, 141 overview, 226, 119, 147 probe source, 226, 124 quantum yields, 226, 139 rhodopsin, 226, 158 sample holders, 226, 133 singular value decomposition, 226, 146, 155 spectral dynamics, 226, 136 time delay generators, 226, 130. 

Fig. 15.14 Analytical techniques for time-resolved headspace analysis. An electronic nose can be used as a low-cost process-monitoring device, where chemical information is not mandatory. Electron impact ionisation mass spectrometry (EI-MS) adds sensitivity, speed and some chemical information. Yet, owing to the hard ionisation mode, most chemical information is lost. Proton-transfer-reaction MS (PTR-MS) is a sensitive one-dimensional method, which provides characteristic headspace profiles (detailed fingerprints) and chemical information. Finally, resonance-enhanced multiphoton ionisation (REMPI) TOFMS combines selective ionisation and mass separation and hence represents a two-dimensional method. (Adapted from [190])...

Baumert, T., Biihler, B., Grosser, M., Thalweiser, R., Weiss, V., Wiedenmann, E., and Gerber, G. (1991). Femtosecond time-resolved wave packet motion in molecular multiphoton ionization and fragmentation, J. Chem. Phys. 95, 8103. 

Time-resolved measurements are also one of the advantages in multiphoton spectroscopy. In the case of nanomaterials, physical and chemical properties are largely affected by interaction with surrounding environments. Therefore, the dynamical study should be useful for characterizing nanomaterials from the viewpoints of nanodevice applications. 

Time-resolved FTIR spectra of Rh4(CO)12 subjected to 266 nm. irradiation in heptane gave evidence for the formation of two isomeric forms of Rh4(CO)n(solv).144 Vibrational assignments were made to vCO modes for gas-phase rhodium cluster carbonyls using IR multiphoton depletion spectroscopy. For Rhn(CO), vCO was at 1950 2 cm-1 (n = 6), 1960-1965 cm-1 (n = 7-11 13-20).145 TRIR data (vCO) were used to follow the formation of intrinsically chiral clusters Rh6(CO)i4(p,K2-PX), where PX = bidentate bridging ligands diphenyl(benzothienyl)phosphine and related systems.146... 

The technique of transient grating spectroscopy has been reviewed, with particular emphasis on its application to monitoring non-radiative deactivation. A unified theory of time-resolved fluorescence anisotropy and Stokes shift spectroscopy has appeared. A separate review has considered the chemical and photophysical events occurring from upper excited states as accessed by multiphoton absorption techniques. ... 

The spectroscopic methods are based on time-resolved pump-probe schemes where the collision-free regime is usually attained by using low pressure conditions. Application of various linear and non-linear laser techniques, such as LIF (laser-induced fluorescence), REMPI (resonant-enhanced multiphoton ionization) and CARS (coherent antistokes Raman spectroscopy) have provided detailed information on the internal states of nascent reaction products [58]. Obviously, an essential prerequisite for the application of these techniques is the knowledge of the spectroscopic properties of the products. 

Thus far, we have examined vibrational spectroscopy using IR absorption spectroscopy, what we called in Ch. 3 one photon method , a general type that encompasses most experiments in spectroscopy. There exist, however, other types of spectroscopy to observe vibrations. These are for instance Raman spectroscopy, which is also of a current use in chemical physics and may be considered a routine method. Other less known methods are modem time-resolved IR spectroscopies. All these methods are two-photon or multiphoton spectroscopies. They do not involve a single photon, as in absorption, but the simultaneous absorption and emission of two photons, as in Raman and in other scattering experiments, or the successive absorption(s) and emission(s) of photons that are coherently delayed in time, as in time-resolved nonlinear spectroscopies. By coherently , we assume the optical waves that carry these two photons keep a well-defined phase difference. In this latter type of spectroscopy, we include all modem set-ups that involve time-controlled laser spectroscopic techniques. We briefly sketch the interest of these various methods for the study of H-bonds in the following subsections. 

A different model describes one specific aspect of laser ablation, i.e., the thermalization of the laser energy in doped polymers. This model is based on spectroscopic data (time-resolved absorption/emission measurements [93, 94] and TOF-MS data [95]), but is mainly valid for irradiation with wavelengths >248 nm, and for polymers which contain polyaromatic compounds as dopants. The mechanism involves a cyclic multiphotonic absorption process with up to ten photons [96]. From the highly excited polyaromatic dopant molecules, the photon energy is transferred to the polymer matrix via rapid internal conversion. The associated temperature increase results in the thermal decomposition of the polymer. From the time-depen-dent absorption studies it was suggested that, in view of their longer lifetimes, excited triplet states should play a key role in this process. 

Multiphoton infrared excitation of the sulfoxide stretching chromophore (ca. 1100 cm ) of DMSO also leads to production of CH3 and SO in their respective electronic ground states [120]. The direct formation of ethane was once again eliminated, this time by product analysis from double label experiments with DMSO and its Dg isotopomer. Time resolved detection of IR absorptions was used to analyze products. Though, once again, CHjSO- was not directly observed, these authors favor a stepwise decomposition because of a nonthermal rotational level distribution of the SO fragment. 

T. Baumert, M. Grosser, R. Thalweiser, G. Gerber, Femtosecond time-resolved molecular multiphoton ionisation the Na2 system. Phys. Rev. Lett. 67,3753 (1991)... 

---