Temporal detuning

The realization of SPODS via PL, that is, impulsive excitation and discrete temporal phase variations, benefits from high peak intensities inherent to short laser pulses. In view of multistate excitation scenarios, this enables highly efficient population transfer to the target states (see Section 6.3.3). Furthermore, PL can be implemented on very short timescales, which is desirable in order to outperform rapid intramolecular energy redistribution or decoherence processes. On the other hand, since PL is an impulsive scenario, it is sensitive to pulse parameters such as detuning and intensity [44]. A robust realization of SPODS is achieved by the use of adiabatic techniques. The underlying physical mechanism will be discussed next. 

The adiabatic passage induced by two delayed laser pulses, the well-known process of STIRAP [69], produces a population transfer in A systems (see Fig. 7a). The pump field couples the transition 1-2, and the Stokes field couples the transition 2-3. It is known that, with the initial population in state 11), a complete population transfer is achieved with delayed pulses, either (i) with a so-called counterintuitive temporal sequence (Stokes pulse before pump) for various detunings as identified in Refs. 73 and 74 or (ii) with two-photon resonant (or quasi-resonant) pulses but far from the one-photon resonance with the intermediate state 2), for any pulse sequence (demonstrated in the approximation of adiabatic elimination of the intermediate state [75]). Here we analyze the STIRAP process through the topology of the associated surfaces of eigenenergies as functions of the two field amplitudes. Our results are also valid for ladder and V systems. 

Figure 12. Transfer efficiencies P2 to 12) (upper row) and P3 to 13) (lower row) as functions of the detunings Ap and As (in units of fimax) at the end of the pulses for the intuitive (left column) and counterintuitive (right column) sequences of delayed sine-squared pulses eith the same peak amplitude flmax and a large temporal area fimaxx = 500 (x is the pulse length and the delay is x/2). The efficient pupulation transfer are bounded by Ap = 0 and As = 0 (thick full lines) and the branches of hyperbolas (dashed lines). The areas bounded by the full lines are labeled by the cases...

Though the switching powers in Fig. 1 show a reduction by an order of magnitude, the temporal response of the device remains virtually unchanged over the same temperature range (Fig. 4). Elevating the temperature from 26.00 to 34.70 C, for the same detuning in each case, reduces the 100% overdrive power from 963 to 87 with no penalty in... 

FIG- 4. Temporal response of > dielectric/fDld 4T15 cell td dilTereiil vmbient UempeTniuriQ wilhoon tuil detuning. (O) 26.00X, ( > 34.70 C. 

Figure 3 is an illustration of the typical temporal variation of the CARS signal intensity, I(At), from LO phonons with to =403 cm and an ambient temperature of 5 K for a GaP crystal with a carrier concentration of less than 10 cm 3. The component of the signal from -40 to 4-20 ps is primarily the result of nonlinear excitation of the electronic system. The full shape of this signal (dashed curve) can be obtained by slightly detuning away from u. 

---