Coherent transients

Morita N and Yajima T 1984 Ultrafast-time-resolved coherent transient spectroscopy with incoherent light Rhys. Rev. A 30 2525-36... 

Loring R F and Mukamel S 1985 Selectivity in coherent transient Raman measurements of vibrational dephasing in liquids J. Chem. Phys. 83 2116-28... 

Figure 4. Coherent transients observed in gases and molecular beams. Shown are the photon echo (detected by spontaneous emission), the free induction decay, and Ti for different pressures (iodine gas and beam).

In real systems the symmetric top parameters A and B may differ in the ground and excited states. Furthermore, when Coriolis coupling is taken into account, K is no longer a good quantum number and the J level spacing is not completely regular. These effects will tend to reduce, but not totally eliminate, recurrences of coherent transients and echoes. 

The microwave detected MODR scheme closely resembles pulsed nuclear magnetic resonance (Hahn, 1950), optical coherent transients by Stark switching (Brewer and Shoemaker, 1971) and laser frequency switching (Brewer and Genack, 1976). The on-resonance microwave radiation field, ojq = ( 2 — Ei)/H, creates an oscillating bulk electric dipole polarization (off-diagonal element of the density matrix, pi2(t)). The oscillation is at u>o u>r, where ojr is the (Mj-dependent) Rabi frequency,... 

There are several classes of optical effects induced by an internal perturbation, such as saturation of absorption, coherent Raman spectroscopy, multi-photon absorption processes, coherent transient spectroscopy (see Table 0.3). Section 5.1 of this chapter deals with saturation of absorption and multi-photon absorption processes. Section 5.2 outlines the principles of coherent anti-Stokes Raman spectroscopy (CARS), Raman-induced Kerr effect spectroscopy (RIKES), four-wave mixing (FWM), and photon echo. 

Another problem of immediate interest to the observation of coherent transients in condensed organic molecules is the question, which electronic state initially is prepared by optical excitation This question, which is the central one in the theory of radiationless processes, has been studied in great detail and the interested reader is referred to a recent review on the subject by Jortner and Mukamel." For optical excitations in solids it seems safe to assume that Born-Oppenheimer singlet and triplet states are the initially prepared states. 

In the previous section we have been confronted with the results of coherent transient experiments which showed that the low-temperature homogeneous lineshape of electronic transitions of impurity molecules is exponentially activated. Next to the optical domain such an exponential activation was observed in the microwave domain by van t Hof and Schmidt and explained on the basis of the modified Bloch equations. 

Some techniques of laser spectroscopy, such as the method of separated fields optical Ramsey fringes. Sect. 9.4), coherent transient spectroscopy (Sect. 7.6), or polarization spectroscopy (Sect. 2.4) allow one to distinguish between phasechanging, velocity-changing, or orientation-changing collisions. 

R.G. Brewer, A.Z. Genack, Optical coherent transients by laser frequency switching. Phys. Rev. Lett. 36, 959 (1976)... 

At higher frequencies, FT spectroscopy is generally carried out with a Michelson interferometer rather than by detection of a coherent transient decay. The Michelson interferometer divides the input radiation into two parts with a beamsplitter and then recombines them. As the optical path difference of the two parts is varied, the interference of the recombined beams produces an interferogram. If the optical path difference, x, changes at a constant rate, v, then the interferogram becomes a function of time, f x)=f vt), and the FT yields the desired spectrum, F(v). In general, double-sided interferograms are... 

The presented results demonstrate that polarization selective, time-resolved coherence spectroscopy can successfully be applied for Doppler-free measurements of large frequency splittings in the 10 GHz range. Fast coherent transients with excellent signal-to-noise ratio have been detected. The investigations show a very satisfactory agreement with the theoreti-... 

These oscillations can sensitively be detected via changes in the polarization of delayed probe pulses. Therefore, the coherently excited sample is placed between crossed polarizers and the transmitted intensity of the probe beam is monitored. By varying the delay time, one can sample the time evolution of the coherent transients. 

In siammary, the preliminary results presented in this contribution already demonstrate that time resolving polarization spectroscopy offers a number of favourable and new features for direct observation of fast evolving events on a femtosecond time scale and detection of oscillations up to the THz-range. The described technique can be applied to free atoms, liquids and solids to measure coherent transients in groimd and excited states. Since the observed beats result from an atomic interference effect, narrow structures which may be hidden by inhomogeneous broadening mechanisms can still be resolved. 

Zamith, S., Degert, J., Stock, S., de Beauvoir, B., Blanchet, V., Bouchene, M.A., and Girard, B., Observation of coherent transients in ultrashort chirped excitation of an undamped two-level system, Phys. Rev. Lett., 87, 033001, 2001. 

Macfarlane, R.M., and R.M. Shelby, 1987, Coherent transient and holebuming spectroscopy of rare-earth ions in solids, in Spectroscopy of Solids Containing Rare-Earth Ions, eds A,A. Kaplyanski and R.M. Macfarlane (North-Holland, Amsterdam) p, 51. Macfarlane, R.M., C.S, Yannoni and R.M. Shelby, 1980, Opt. Commun. 32, 101. 

Shelby et al extended the optical detection scheme for solid-state NMR, used by Erickson/to the investigation of rf coherent transients in nuclear hyperfine substates of dilute Pr " in LaFs at They observed rf... 

A. J. M. Kiruluta, Functional Dopant Profiling of Optical Coherent Transient Materials , Prog. Quantum Electron., 2007, 31, 217. 

A number of laser based temporal domain experiments have evolved in the past two decades which have no equivalents in conventional spectroscopic technique as they exploit the coherence inherent to stimulated sources. The origin of these methods traces directly to techniques which are widely utilized in NMR and ESR spectroscopy to determine various relaxation and dephasing times. In fact, much of the terminology from magnetic resonance processes has been carried over to laser driven coherent transient studies. See Shoemaker (1978), Levenson (1982) and Brewer and DeVoe (1984). 

Many experimental variations of these coherent techniques have been developed but basically the experiments may be divided into two classifications, i.e. coherent transient technique and photon echo phenomena, the former requires high resolution, high stability sources while the latter relies on sequential pulse excitation with controlled delays. 

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