Optical pulse-shaping for internal cooling of molecules

Abstract

We consider the use of pulse-shaped broadband femtosecond lasers to optically cool rotational and vibrational degrees of freedom of molecules. Since this approach relies on cooling rotational and vibrational quanta by exciting an electronic transition, it is most easily applicable to molecules with similar ground and excited potential energy surfaces, such that the vibrational state is usually unchanged during electronic relaxation. Compared with schemes that cool rotations by exciting vibrations, this approach achieves internal cooling on the orders-of-magnitude faster electronic decay timescale and is potentially applicable to apolar molecules. For AlH(+), a candidate species, a rate-equation simulation indicates that rovibrational equilibrium should be achievable in 8 μs. In addition, we report laboratory demonstration of optical pulse shaping with sufficient resolution and power for rotational cooling of AlH(+).

Electronic spectroscopy of a cold SiO+ sample: Implications for optical pumping

“…This technique was first demonstrated by vibrationally cooling Cs2 14 . It was also proposed that for a transition with diagonal FCFs, applying a sharp cutoff at the right frequency such that P-branch transitions are predominately driven will cause rotational cooling [15][16][17] . Rotational cooling by this method was first demonstrated 9 with trapped AlH + .…”

Quantum logic for the control and manipulation of molecular ions using a frequency comb

“…One approach to decrease the number of populated rotational states is optical pumping with spectrally shaped broadband light [19][20][21]. For the X 2 + (ν = 0) → B 2 + (ν = 0) transition in SiO + , the R (J → J + 1 transitions) and P (J → J − 1 transitions) branches are well separated (see figure 3).…”

“…Several methods for preparing molecular ions in a single quantum state have recently been demonstrated: for example optical pumping assisted by black body radiation [15,16] and sympathetic cooling of translational degrees of freedom for molecular ions formed in a particular rovibrational state [18]. Other promising techniques, such as optical pumping using broadband light [19][20][21], sympathetic cooling of molecular ions in a cloud of ultracold neutral atoms [22] and cavity cooling [23,24], have also been proposed and are currently under active experimental investigation.…”

Resonant few-photon excitation of a single-ion oscillator

“…Implementation of sustained amplification with phase-sensitive detection, along with other technical improvements discussed above, could reduce scattering to the small number (order 100 and N = 1) required to make a seeded excitation detectable above the thermal and scattering noise. With a cotrapped fluorescing ion used for the amplification and detection, this motional seeding technique could be useful in spectroscopy experiments on molecular ions with semiclosed transitions [19,22,23], atomic ions with slow cycling transitions, and in bichromatic force schemes where cycling is enhanced by stimulated emission [24][25][26]. This resonant impulsive excitation technique could also be used to coherently excite selected normal modes of larger trapped ion crystals.…”