Infrared pulses, generation

A state-of-the-art description of broadband ultrafast infrared pulse generation and multichannel CCD and IR focal plane detection methods has been given in this chapter. A few poignant examples of how these techniques can be used to extract molecular vibrational energy transfer rates, photochemical reaction and electron transfer mechanisms, and to control vibrational excitation in complex systems were also described. The author hopes that more advanced measurements of chemical, material, and biochemical systems will be made with higher time and spectral resolution using multichannel infrared detectors as they become available to the scientific research community. 

Infrared pulses of 200 fs duration with 150 of bandwidth centred at 2000 were used in this study. They were generated in a two-step procedure [46]. First, a p-BaB204 (BBO) OPO was used to convert the 800 mn photons from the Ti sapphire amplifier system into signal and idler beams at 1379 and 1905 mn, respectively. These two pulses were sent tlirough a difference frequency crystal (AgGaS2) to yield pulses... 

Richter L T, Petralli-Mallow T P and Stephenson J C 1998 Vibrationally resolved sum-frequency generation with broad-bandwidth infrared pulses Opt Lett. 23 1594-6... 

Shirakawa A, Sakane I and Kobayasi T 1998 Pulse-front-matched optical parametric amplification for sub-10 fs pulse generation tunable in the visible and near infrared Opt. Lett. 23 1292-4... 

Petrov, G. L, Yakovlev, V. V., and Minkovski, N. I. 2003. Near-infrared continuum generation of femtosecond and picosecond pulses in doped optical fibers. Appl. Phys. B 77 219-25. 

Flow measurement has been achieved without the use of beads or dyes. A short heating pulse generated by a C02 infrared laser (10.6 pm) was delivered through the IR-transparent Si wafer into the channel. The radiative image of the hot liquid plug was recorded by an IR camera [414]. 

Richter LJ, Petralli-Mallow T, Stephenson JC. Vibrationally resolved sum-frequency generation with broadband infrared pulses. Optics Lett 1998 23 1594-1596. 

In the experiments described here, two separate techniques have been used for interferometric characterization of the shocked material s motion frequency domain interferometry (FDI) [69, 80-81] and ultrafast 2-d spatial interferometric microscopy [82-83]. Frequency domain interferometry was used predominantly in our early experiments designed to measure free surface velocity rise times [70-71]. The present workhorse in the chemical reaction studies presented below is ultrafast interferometric microscopy [82], This method can be schematically represented as in Figure 6. A portion of the 800 nm compressed spectrally-modified pulse from the seeded, chirped pulse amplified Ti sapphire laser system (Spectra Physics) was used to perform interferometry. The remainder of this compressed pulse drives the optical parametric amplifier used to generate tunable fs infrared pulses (see below). 

The experiments are performed with a modelocked Nd YLF laser system of 10 Hz repetition rate. Tunable infrared pulses are generated by difference frequency mixing between... 

Figure 12.17 (a) Schematic of the AFM-IR experimental setup, (b) The sample is deposited on the upper side of the ZnSe IRE and illuminated by the pulsed infrared pulsed laser. The resulting photothermal expansion generates a brief force under the AFM tip inducing the ringing of the AFM... 

Infrared pulses used for ultrafast time-resolved infrared spectroscopic measurements have been generated mainly by the following three methods ... 

By irradiating the vapors of metals such as Ba and Cs with ultrashort laser pulses, infrared pulses are generated by the process of stimulated electronic Raman scattering. 

Infrared pulses at frequency Vp, are generated as the difference frequency between two ultrashort pulses at frequencies vj and V2 (i.e., vp, = vj - vj vj > V2>. Examples of nonlinear crystals used for the generation of a difference frequency are LiI03 and AgGaS2. 

The transient infrared absorption spectra of molecules in excited electronic states were measured by Elsaesser and Kaiser [18]. The probe pulses used were (i) picosecond infrared pulses in the wavenumber region of 3500-3000 cm generated by an OPA in LiNb03 excited by the Nd YAG laser line, and (ii) picosecond infrared pulses in the region of 3000-1400 cm i obtained by the difference-frequency generation in AgGaS2 between the Nd YAG laser line and near-infrared dye-laser lines excited by the same Nd YAG laser line. 

Snee et al. [26] obtained broadband femtosecond infrared pulses (FWHM about 200 cm ) by the difference-frequency generation in LiI03 between the fundamental... 

In 2005, Towrie et al. [30] developed another time-resolved infrared spectrometer capable of performing femtosecond to microsecond time-resolution measurements, by adding to their spectrometer described in Ref [29] a sub-nanosecond Q-switch Nd YV04 laser (wavelength 1064 nm, pulse width 0.6 ns). The pulses generated by this laser were electronically synchronized with the probe pulses with about 0.3 ns jitter, and the harmonics of pulses from this laser were used as the pump pulses. 

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