We propose adiabatic passage control scheme to maximize coherence in selected vibrational mode. We demonstrate possibility for sustaining high coherence in the presence of dephasing by two chirped pulse trains. Method may enhance CARS imaging.
We propose the adiabatic passage control scheme to maximize coherence in a predetermined molecular vibrational mode via two-photon Raman transitions. We investigate vibrational energy relaxation and collisional dephasing as factors of coherence loss, and demonstrate the possibility for sustaining high value of coherence in the presence of dephasing by two chirped pulse trains. The proposed method may be used to advance imaging techniques currently applied in the coherent anti-stokes Raman scattering (CARS) microscopy.
We discuss a novel method to create maximum coherence in a two-level system that is selectively excited among many having similar frequencies by making use of two specifically chirped pulses in the Raman configuration. The feasibility of the method is analyzed in the presence of decoherence caused by vibrational energy relaxation and collisional dephasing. It has been demonstrated that a high value of coherence may be sustained by the implementation of two chirped pulse trains prepared in accordance with the proposed method and having the same period as the vibrational energy relaxation time. Maximum coherence between predetermined states in atoms and molecules is an important aspect of many problems in quantum optics. One possible example is the generation of optimal CARS signal in the CARS microscopy aiming to reveal structures constituted of particular molecular groups. Presently, in experiments on biological imaging, the CARS signal is generated with implementation of picosecond laser pulses (1), a narrow spectral bandwidth of which allows one to address a particular molecular group with a good accuracy. Aiming to improve chemical sensitivity and to get optimal CARS signal for given pulse intensity we propose to use the quantum control methods for selective excitation of required vibrations in complex molecular systems. We developed a novel method that allows one to achieve maximum coherence in a predetermined vibrational mode in a multimode mole- cular system via the Raman transitions induced by the pump and Stokes chirped pulses. According to the Maxwell-Bloch equations, maximum coherence is the condition for the CARS signal to acquire the highest intensity upon propagation through a molecular medium (2). The mechanism of creation of maximum coherence underlying the proposed method is based on the adiabatic passage. An important aspect in the investigations asso- ciated with a condense phase is decoherence. Two main sources of decoherence, the vibrational energy relaxa- tion and collisional dephasing, may significantly affect the CARS signal intensity. The phase control of molecular processes in the presence of collisions was
We discuss a novel method to create maximum coherence in a two-level system that is selectively excited among many having similar frequencies by making use of two specifically chirped pulses in the Raman configuration. The feasibility of the method is analyzed in the presence of decoherence caused by vibrational energy relaxation and collisional dephasing. It has been demonstrated that a high value of coherence may be sustained by the implementation of two chirped pulse trains prepared in accordance with the proposed method and having the same period as the vibrational energy relaxation time.