Stimulated resonant Raman transition

Fig. 9.83 Stimulated resonant Raman transition spectroscopy with subnatural linewidth resolution (a) level scheme (b) experimental arrangement...

Fig. 9.84 (a) Potential diagram of the Cs2 molecule with the stimulated resonance Raman transitions to high-lying vibration-rotation levels of the ground state, (b) Comparison of... 

Often the super-high spectral resolution of the induced resonant Raman transitions obtained with single-mode lasers is not necessary if the levels m) are separated by more than one Doppler width. Then pulsed lasers can be used for stimulated emission pumping [600]. Many experiments on high vibrational levels in the electronic ground state of polyatomic molecules have been performed so far by SEP with pulsed lasers. Compilations may be found in [601-604]. 

After an initial peak at delay times where the pump and the probe fields overlap, the pump-probe signal is seen to split up into two components a dominant, slightly oscillating feature centered at the electronic gap A of the 5q-52 transition u>2 4.8 eV), and a weaker red-shifted contribution, centered at L02 3.4 eV. As is shown below, the first component at o 2 A is mostly due to stimulated resonance Raman scattering, thus reflecting... 

Ifourth(fd, 2 Q) was multiplied with a window function and then converted to a frequency-domain spectrum via Fourier transformation. The window function determined the wavenumber resolution of the transformed spectrum. Figure 6.3c presents the spectrum transformed with a resolution of 6cm as the fwhm. Negative, symmetrically shaped bands are present at 534, 558, 594, 620, and 683 cm in the real part, together with dispersive shaped bands in the imaginary part at the corresponding wavenumbers. The band shapes indicate the phase of the fourth-order field c() to be n. Cosine-like coherence was generated in the five vibrational modes by an impulsive stimulated Raman transition resonant to an electronic excitation. 

For momentum transfer stimulated Raman transitions between the two hyperfine levels 1 and 2) of the Na(3 5 i/2) state are used, which are induced by two laser pulses with light frequencies coi and o)2 (o) —002 = < hfs) traveling into opposite directions (Fig. 9.71b). Each transition transfers the momentum Ap 2hk. The gravitational field causes a deceleration of the upwards moving atoms in the fountain. This changes their velocity, which can be detected as a Doppler shift of the Raman transitions. Because the Raman resonance a)i—a)2 = has an extremely narrow... 

On the basis of the experimental data presented above, one cjin exclude on the onset several models for the "blue peak" emission. Firstly, spin-flip collision induced population inversion on the Di transition is not involved - due to both the off-resonant character of the emission and its independence on the buffer gas pressure. Similarly, pressure induced extra resonances are rejected. Stimulated electronic Raman and three photon scattering effects, both by a two or three level system, are dependent on the laser detuning and neither their frequencies are to the blue in the vicinity of the Di line (figure 2) thus, these processes are also excluded. 

Figure 6.1 Nonlinear optical responses, (a) Second-order SF generation, the transition probability is enhanced when the IR light is resonant to the transition from the ground state g to a vibrational excited state V. CO is the angular frequency of the vibration, (b) Third-order coherent Raman scheme, the vibrational coherence is generated via impulsive stimulated...

Coherent excitation of quantum systems by external fields is a versatile and powerful tool for application in quantum control. In particular, adiabatic evolution has been widely used to produce population transfer between discrete quantum states. Eor two states the control is by means of a varying detuning (a chirp), while for three states the change is induced, for example, by a pair of pulses, offset in time, that implement stimulated Raman adiabatic passage (STIRAP) [1-3]. STIRAP produces complete population transfer between the two end states 11) and 3) of a chain linked by two fields. In the adiabatic limit, the process places no temporary population in the middle state 2), even though the two driving fields - pump and Stokes-may be on exact resonance with their respective transitions, 1) 2)and... 

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]... 

The experiments discussed in this book are diverse, but they break down into two broad categories (1) resonant infrared methods in which ultrafast IR pulses are tuned to the wavelength of the vibrational transition and (2) Raman methods (in some instances referred to as impulsive stimulated scattering), in which two visible wavelengths have a difference in frequency equal to the vibrational frequency. In some experiments, infrared and Raman techniques are combined in a single measurement. 

Up to now/ the dimer laser system has been described alone in terms of population inversion between suitable energy levels/ and for this description the condition S2 > A 2 is indeed the only necessary condition for cw laser oscillation/ as long as the thermal population density in the lower laser level remains negligibly low. However/ as this optically pumped laser system is a coherently excited three level system/ the coherent emission can also be described as stimulated Raman scattering/ which is resonantly enhanced by the common level 3 of the pump and laser transitions. This coupled two photon or Raman process does not require a population inversion between levels 3 and 2 and introduces qualitatively new aspects which appreciably influence and change the normal laser behaviour. For a detailed and deeper description of the coherently excited three level dimer... 

In the A-type OODR scheme (Fig. 5.32) the probe laser induces downward transitions from the upper level = 2) of the pump transition to lower levels / = m). This process, which is called stimulated emission pumping (SEP), may be regarded as a resonantly induced Raman-type transition. In case of monochromatic pump and probe lasers tuned to the frequencies co and co2, respectively, the resonance condition for a molecule moving with velocity v is... 

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