Speaker
Description
Coherent anti-Stokes Raman Spectroscopy (CARS) being one of the important measurement techniques in reactive flows, we present a novel method to improve its diagnostic ability using quantum control. This is achieved by carefully engineering the interference of two confined quantum wavepackets, by the implementation of 2- beam hybrid fs/ns rotational CARS along with a second (control) pulse with a variable delay. Initially, the fs pulse involved in the fs/ns CARS process creates a rotational wavepacket. Then, if the control pulse arrives at an integer multiple of the molecular revival period (Trev), a wavepacket that is exactly in phase with the initial wavepacket is created, resulting in constructive interference, i.e. signal amplification. This is particularly useful in high temperature applications where species number density is lower. On the other hand, if the control pulse arrives at an integer multiple of half the molecular revival period (Trev/2), a wavepacket that is exactly in anti-phase with the initial wavepacket is created, resulting in destructive interference, i.e. signal annihilation. This can be used to improve the species-specific detection as we can annihilate specific molecular fingerprint in a mixed volume. The technique can also create spin isomer selective excitation, if the control pulse delay is quarter the molecular revival period (Trev/4). Improved species selectivity and measurement accuracy in real time environments, with spectroscopic applications in non-stationary and unpredictable reacting flows, can be obtained by selecting a delay time that is optimal for the desired purpose.
