Transform-limited pulse

Greenfield S R and Wasielewski M R 1995 Near-transform-limited visible and near-IR femtosecond pulses from optical parametric amplification using Type II p-barium borate Opt. Lett. 20 1394-6... 

Figure 7.1 Selective excitation of only one multiplet by a selective pulse transforms a 2D experiment into a ID technique. A selective pulse generates the transverse magnetization. The result is a trace of the corresponding 2D spectrum. (Reprinted from Mag. Reson. Chem. 29, H. Kessler ei al., 527, copyright (1991), with permission from John Wiley and Sons Limited, Baffins Lane, Chichester, Sussex P019 lUD, England.)...

The second example is the quadratically chirped pump-dump scheme. Since the pioneering work by Tannor and Rice [119], the pump-dump method has been widely used to control various processes. However, since it is not possible to transfer a wave packet from one potential energy surface to another nearly completely by using the ordinary transform limited or linear chirped pulses, the... 

Ultrafast time-resolved resonance Raman (TR ) spectroscopy experiments need to consider the relationship of the laser pulse bandwidth to its temporal pulse width since the bandwidth of the laser should not be broader than the bandwidth of the Raman bands of interest. The change in energy versus the change in time Heisenberg uncertainty principle relationship can be applied to ultrafast laser pulses and the relationship between the spectral and temporal widths of ultrafast transform-limited Gaussian laser pulse can be expressed as... 

Fig. 3.14. Left transient reflectivity change of Te obtained with transform limited, negatively chirped, and positively chirped pulses. Right coherent phonon amplitude as a function of the pulse chirp. Adapted from [42]...

Dudovich, N., Dayan, B., Eaeder, S. M. G., and SUberberg, Y. 2001. Transform-limited pulses are not optimal for resonant multiphoton transitions. Phys. Rev. Lett. 86 47-50. 

The CC pulse train experiments in Refs [63-65] utilize shaped pulses that use a transform-limited (TL) Gaussian pulse its phase is modulated in the frequency domain with a sine function, p ( ) = a sin( -I- c), while keeping the amplitude profile intact. The parameters a, b, and c are further varied to control molecular populations. In Reference [35], the effect of different values of these parameters on the IC dynamics of pyrazine and / -carotene is investigated and the significant role of overlapping resonances is exposed. 

Figure 9.21 The angular distribution (relative to the polarization direction) of the H+H photofragments as a function of their kinetic energy release by a transform-limited pulse with peak intensity (/peajj = 3 X 10 W/cm ). (a) Computed (b) experiment (according to Ref. [94]). Taken from Ref. [43].

The MIIPS of compensated pulses is shown in Fig. lb. To corroborate phase information retrieved from MIIPS, phase characterization was also done using second harmonic generation frequency resolved optical gating (SHG-FROG) [7], SHG-FROG traces of the pulses before and after compensation are shown in Fig. lc and Id. The final pulse-shaping step involved the controlled phase modulation of transform-limited pulses. 

Fig. 3. Experimental demonstration of two-photon selective microscopy. The HPTS-labeled sample being imaged has acidic (bottom side) and a basic (top side) regions. Images were obtained with (A) 23-fs transform-limited pulses centered at 842 nm, and (B and C) phase shaped pulses optimized for selective excitation.

Fourier Transform-limited 100 fs, 800 nm, 1015 W cm 2 laser pulse and (b) the optimum result obtained by means of an 80-parameter unrestricted optimisation (dashed line) and a restricted 3-parameter optimisation (full line). The inset in (b) shows the evolution of the fitness value for the 80 parameter optimisation (full squares maximum fitness, open squares average fitness), (c) Autocorrelation trace of the optimal pulse corresponding to the 80 parameters optimisation. The pulse shapes consists of two pulses of 120 fs of equal amplitude separated by 500 fs. 

Fig. 2a displays the ion time-of-flight (TOF) distribution obtained when (n) = 1.6 104 Xe clusters interacted with a Fourier Transform-limited 100 fs 800 nm, 1015 W cm 2 laser pulse. The TOF displays a number of peaks corresponding to ions up to Xe1,+. The peaks in the TOF are quite broad, and even display a double peak structure due to the fact that ions are emitted in forward-backward directions with respect to the detector. Both the charge state reached and the kinetic energy of the ions are signatures of collective effects in the cluster ionisation. For example, when only atoms were present in the atomic beam, the maximum charged state reached was 4+. 

The results of two different optimisations of the production of charged states >11+ are presented in Fig. 2b. The dashed curve is the TOF distribution obtained when optimising 80 independent phases across the spectrum. By contrast with the Fourier Transform-limited pulse, ions up to 25+ are present in the TOF distribution The corresponding pulse shape (as determined from the autocorrelation in Fig. 2c) is a sequence of two pulses of equal amplitude and separated by 500 fs. To test the importance of the time delay between the two pulses, we performed restricted optimisations where a periodic phase was applied across the spectrum along with a quadratic term. In this case the period and amplitude of the oscillatory part... 

We study two adiabatic schemes that, use a sequence of time-delayed transform limited pulses. The first one, known as STIRAP (Stimulated Raman adiabatic passage) controls the population transfer between three vibrational states. The frequency of the first pulse (t)[ is tuned in resonance with the transition from 4> (x) to the intermediate state (f>i0 x), and the frequency of the second pulse [ 2(t)] is resonant with the transition from i0 x) to 4>q x) i0 x) is the intermediate state that maximizes the Franck-Condon factors for both transitions at the same time, working as an efficient wave function bridge between the initial and target wave functions [5]. Using counterintuitive pulses, such that (t) precedes x (t), the wave function of the system has the interesting form [3]... 

Here we report our exploration of the possibility of inducing an ultrafast non-Franck-Condon transition, which we defined to be the creation of a wave packet at the other turning point of the above-mentioned oscillation, see Fig. 1(b), faster than the time it takes the Franck-Condon packet to reach that turning point due to the natural (field-free) dynamics. We have explored two possible routes for inducing non-Franck-Condon transitions, namely phase-tailoring of a weak-field ultraviolet (UV) pulse [6] tmd a two-pulse scheme combining a transform limited weak-field UV pulse with a strong infrared (IR) field [7]. 

The experimental configuration of the pump-probe experiment is similar to Ref. [5]. A home built non-collinear optical parametric amplifier (nc-OPA) was used as a pump, providing Fourier-transform-limited 30 fs pulses, which could be spectrally tuned between 480-560 nm. In all experiments white-light generated in a sapphire crystal using part of the fundamental laser (800 nm), was used as probe light. In the pump-probe experiments the pump was tuned to the S2 0-0 band for carotenoids with n>l 1. In the case of M9, it was not possible to tune the nc-OPA to its 0-0 transition, and hence another nc-OPA tuned to 900 nm was frequency doubled and used for excitation. In addition to conventional transient absorption pump-probe measurements, we introduce pump-deplete-probe spectroscopy, which is sensitive to the function of an absorbing state within the deactivation network. In this technique, we... 

Transform-limited (TL) visible pulses with as short as sub-5-fs duration have been generated from a noncollinear optical parametric amplifier and applied to the study of polyacetylene, polydiacetylene, azobenzene, and J-aggregates of porphyrin for optical -devices. 

Transform-limited (TL) visible pulses with as short as 3.9 and 4.7-fs duration have been generated from noncollinear optical parametric amplifiers (NOPA)[l-7], and they were applied to the study of various systems [8-14], We reported several new phenomena the direct observation of transition state during photochemical reaction by probing the change in the electronic transition probability induced by nuclear motion. In this paper four subjects are discussed. They are (1) NOPA, (2) polyacetylene, (3) polydiacetylene and (4) bacteriorhodopsin. 

Figure 9. (a) Electron spectra measured with single up-chirped (+3500-fs2) down-chirped (-3500-fs2) and unchirped laser pulses. The transform-limited pulses of 40 fs duration are centred at a wavelength of 618 nm. The chirped pulses are of 240 fs duration, (b) Calculated spectra using the same parameters as (a). 

Figure 11. The Na+ fragment TOF spectra obtained with single long (chirped) pulses of 240 fs duration and 40-fs transform-limited laser pulses at 618 nm. The ratio of low energetic versus high energetic fragments is seen to be influenced by the pulse duration.

Figure 14. (a) Transient two-photon ionization spectrum of Na3 recorded with transform-limited 60-fs pulses. (b) The corresponding Fourier transform shows only the breathing mode of the relating B state [13]. 

Figure 11. Comparison between the expectation values of several observables pertaining to the state of the linear HCCH molecule at the end of the pulse for various transform-limited pulses. A 91-state active bright-state basis approximation is compared with the result of a full calculation (labeled DVR).

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