Laser hole burning

Laser hole-burning experiments in the nanosecond time domain can reveal the picosecond time history of the relaxation times in an n-level system of the molecule if those relaxation times are fast (picosecond) compared to the duration of the laser saturating pulse (nanosecond). Under these circumstances, the levels of the system can be treated as photostationary states and the kinetic equations solved exphcitly for the rate constant between any two specified levels. This leisurely approach to picosecond phenomena is equally valid in the picosecond time domain. 

The second method is the laser hole-burning method. By firing the excimer laser at the parent molecular beam, the intensity of the parent molecules along the detector axis is reduced for a time equal to the pulse width (full width = 16 ns) of the laser. The reduction of the parent beam signal is due to the dissociation of the parent molecule induced by the absorption of a 193-nm photon. The laser burn hole recorded by the MCS gives an accurate measure of the velocity spread and the most probable speed (vq) of the parent molecular beam traveling from the photodissociation region to the ionizer. 

To obtain the Vq value for the parent molecular beam, the speed profile for the parent molecular beam obtained by the chopper wheel or the laser hole-burning method is fitted to an assumed number density distribution of the form f v) r exp[ —(r — Lo)V(Ai ) ], where Av is a measure of the width of the speed profile. 

Figure 3. Laser-hole-buming spectra for CSj in (a) a pure CSj beam Pq = 150Torr), (b) a CS2/Ne seeded beam (Pq = 517Torr), (c) a CSj/He seeded beam (Pq = 362 Torr), and (d) CSj/He seeded beam (upper spectrum) (Pq = 776 Torr) and laser hole-burning spectrum for ( 82)2 in CSj/He seeded beam (lower spectrum) (Po = 776 Torr). L = 84.5 cm. Taken from ref 70.

Figure 4. Upper spectrum SO2 beam pulse produced in a 20% SOj and 80% Ar seeded mixture. Lower spectrum laser hole-burning spectrum for SOj. Pq = 1465 Torr and L = 65.5 cm.

Laser hole-burning experiments 393 10. Nuclear magnetic resonance 395... 

MAGNETIC RESONANCE SPECTROSCOPY AND HYPERFINE INTERACTIONS 393 9.3. Laser hole-burning experiments... 

In contrast to the previous experiments with dilute rare-earth ions, quadrupole splittings in the ground ( F ) and excited ( Z>o) states of Eu " in the stoichiometric rare-earth compound EuPsOu were also determined by laser hole burning and optically detected... 

Figure B2.1.7 Transient hole-burned speetra obtained at room temperature with a tetrapyrrole-eontaining light-harvesting protein subunit, the a subunit of C-phyeoeyanin. Top fluoreseenee and absorption speetra of the sample superimposed with die speetnuu of the 80 fs pump pulses used in the experiment, whieh were obtained from an amplified CPM dye laser operating at 620 mn. Bottom absorption-diflferenee speetra obtained at a series of probe time delays.

Fig. 22. Photochemical hole burning (PHB) (1,173) where CO is frequency CO, frequency of the laser and CO p, frequency of the photoproduct.

Laser-induced multiphoton ionization and hole burning spectroscopy... 

These hole-burning effects in intracavity absorbers have attracted increapd interest because they are, besides their application to high-resolu on spectroscopy, surprisingly useful for extreme frequency stabilization of gas lasers, as will be shown in the next section 339a)... 

Figure 18 Comparison of optical absorption data and TEM images (at the same magnification) for two gold samples irradiated by laser pulses having the same fluence (0.25 J cm ) and different pulse width. Top with a 7-nsec laser pulse at 800 nm. (a) Partial melting of the gold nanorods and (b) selective optical hole burning in the near-IR band corresponding to the nanorods. Bottom with laser pulses of 100 fsec. (c) Complete melting of the gold nanorods into nanodots and (d) complete depletion of the nanorod band. (From Ref 211.)...

Figure 7.32 (a) Broadening of an electronic absorption band of a molecule due to an inhomogeneous environment (b) illustration of a laser-induced photochemical hole burned in the 0-0 A, line of free-base porphyrin in -octane at 2K (c) excitation spectrum of the 0-0 lines of the Sj-So transition of the free base in n-hexane, showing a frequency difference ( 100cm" ) between the two tautomeric forms (1) and (2) of the free base in a single type of site. Irradiation into the line A, transforms it into Aj and vice versa (d) hole burned in line A, at 4.2 K. (After Williams, 1983.)... 

R. de Vivie-Riedle and J. Manz Prof. Neumark s question about detecting the hole burning in the nuclear wavepacket of the electronic ground state is very stimulating. In this context, we have developed a scheme for detecting the hole in the wavepacket by a femtosecond chemistry laser experiment that involves two laser pulses Our explanation will be for the specific system K2, but more general applications for other systems are obvious ... 

The sequence of these laser pulses for hole burning and probing may be called bum and probe. It is illustrated by model simulations in Fig. 1 (see pages 197 and 198). Our scheme is an extension of the pioneering work of Kosloff et al. on hole burning in nuclear wavepack-ets [3—9] see also Ref. 10 (supported by Deutsche Forschungsgemein-schaft). 

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