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Physical Review A

All-optical cw quadruple resonance excitation: A coherently driven five-level molecular system

Ergin H. Ahmed, Peng Qi, A. M. Lyyra

Published Jun 18, 2009• 9 citations
Publisher

Abstract

We report here a continuous-wave, high-resolution, and all-optical quadruple resonance laser excitation experiment. To demonstrate this excitation technique, we have used an inhomogeneously broadened molecular sample $({\text{Na}}_{2})$. We emphasize the enhanced ability afforded by the technique to reach new ranges of internuclear separation as well as access to a large range of molecular electronic states. Using the Autler-Townes split line shape of a rovibronic transition and the $E$ field amplitude of the corresponding coupling laser, we have measured with high precision the absolute value of the molecular electronic transition dipole moment matrix elements, with more flexibility than the double and the triple resonance based excitation schemes used previously. This technique may also be used in a stimulated Raman adiabatic passage configuration for effective transfer of ultracold molecules, formed at long internuclear distance, to the lowest vibrational level of the ground electronic state.

DOI
10.1103/physreva.79.062509

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All-optical quantum control of angular momentum orientation and high-resolution spectroscopy of alkali dimers

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In this dissertation, three distinct but related experimental works are reported. The first is a study of the highly excited 3^1 Δ_g and 4^1 Δ_g electronic states of 85Rb2. Rovibrational levels of the two electronic states were probed using the high-resolution optical-optical double resonance (OODR) technique by exciting 85Rb2 molecules from thermally populated levels of the X(_ ^1)Σ_g^+ ground state through intermediate levels of the B^1 Π_u electronic state. The (_ ^1)Δ_g resonances induced by the probe laser were observed by detecting laser induced fluorescence (LIF) from nearby, collisionally populated triplet levels to the a^3 Σ_u^+ triplet ground state. The (_ ^1)Δ_g character of the two electronic states was confirmed by showing that the probe transitions to these states abide by (_ ^1)Δ←(_ ^1)Π dipole selection rules and by observing that their lowest rotational level is J = 2. A set of molecular constants and a Rydberg-Klein-Rees (RKR) potential energy curve (PEC) were calculated from the observed term values for each electronic state and compared with ab initio predictions. This is the first observation of (_ ^1)Δ_g states in Rb2.The next results are on the highly excited 6(_ ^3)Π_0g electronic state of the 133Cs2 molecule in an energetic region where very little is known. Rovibrational levels of the excited triplet state were experimentally observed by the perturbation-facilitated-OODR (PFOODR) using a level of the A(_ ^1)Σ_u^+ ~b(_ ^3)Π_u mixed manifold as an intermediate. A progression of P and R branch probe laser resonances were detected by measuring (LIF) to the a(_ ^3)Σ_u^+ state as a function of the probe laser frequency. For select rovibrational levels of the 6(_ ^3)Π_0g state, dispersed fluorescence to the a(_ ^3)Σ_u^+ state and the A(_ ^1)Σ_u^+ ~b(_ ^3)Π_u manifold were also recorded and compared with Frank-Condon factor (FCF) calculations to determine spin multiplicity and vibrational numbering. Term values of the 284 observed rovibrational levels and their quantum numbers were fit to a Dunham expansion to obtain molecular constants, which were in turn used to generate a corresponding RKR-PEC. Comparison to ab initio results led to the assignment of 6(_ ^3)Π_0g . Accurate and high-resolution potential energy curves for the excited states of alkali dimers are crucial for quantum control and cooling experiments relying on techniques such as Stimulated Raman adiabatic passage (STIRAP) and resonantly enhanced multiphoton ionization (REMPI).Lastly, the results of producing state selective molecular angular momentum orientation using dressed states created by a cw optical field are reported. The experiment was carried out with 7Li2 molecules and a combination of left- and right-hand circularly polarized lasers. Our approach exploits the dependence of the Rabi frequency on the quantum number M, which makes it possible to achieve complete M-state selectivity and thus molecular angular momentum orientation relative to laboratory frame space-fixed axes. Using molecules in a (_ ^1)Σ state, orientation of the rotational angular momentum, R ⃑, can be achieved by spectrally resolving the Autler-Townes split M components of the total angular momentum, J ⃑. Results of orienting J ⃑ in (_ ^1)Π state molecules are also discussed. This is the first time complete angular momentum orientation has been achieved in nonpolar molecules and should aid the efforts of stereochemistry, molecular imaging, photodissociation and photoassociation, to name a few.

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This thesis reports the creation and trapping of 87RbCs molecules in the absolute ground state with a temperature of 1 uK. We build a tunable narrow-linewidth laser system at 1550 nm and 980 nm, using a single high-finesse optical cavity as a reference for both colours. We use fibre-coupled electro-optic modulators to continuously tune both lasers. These allow a novel measurement of the free spectral range of the cavity to better than 1 part in 10^6. We perform one- and two-photon spectroscopy on 87RbCs Feshbach molecules and identify a suitable intermediate state for transfer to the molecular ground state. We measure the electric dipole moment of the molecular ground state as 1.225(3)(8) D, and demonstrate the highest lab-frame dipole moment of any ultracold molecular system at the time of measurement. We transfer the molecules to the electronic, rovibrational and hyperfine ground state using stimulated Raman adiabatic passage, with 88% efficiency. We measure the transition strengths and excited state linewidth for this transfer route. We develop a model for the transfer which includes the effect of laser linewidth, and find excellent agreement with experimental data. The molecular sample is trapped in an optical dipole potential, and has a lifetime of 0.89(6) s. We reference the STIRAP lasers to a novel design of frequency comb which uses difference frequency generation to cancel the carrier-envelope offset. We use this to measure the binding energy of the molecules as h x 114 268 135.24(4)(3) MHz. To our knowledge, this is the most precise determination of the dissociation energy of a molecule to date. Finally, we report progress toward loading the molecules into a 1D optical lattice at 1064 nm. We develop the tools and methods to characterise a lattice, and demonstrate trapping of Feshbach molecules in both a 1D optical lattice and a harmonic optical potential at 1064 nm.

•Jan 1, 2016•0 citations
We report here a continuous-wave, high-resolution, and all-optical quadruple resonance laser excitation experiment. To demonstrate this excitation technique, we have used an inhomogeneously broadened molecular sample (Na2)({\text{Na}}_{2})(Na2​). We emphasize the enhanced ability afforded by the technique to reach new ranges of internuclear separation as well as access to a large range of molecular electronic states. Using the Autler-Townes split line shape of a rovibronic transition and the EEE field amplitude of the corresponding coupling laser, we have measured with high precision the absolute value of the molecular electronic transition dipole moment matrix elements, with more flexibility than the double and the triple resonance based excitation schemes used previously. This technique may also be used in a stimulated Raman adiabatic passage configuration for effective transfer of ultracold molecules, formed at long internuclear distance, to the lowest vibrational level of the ground electronic state.
One possibility for the creation of ultracold, high phase space density quantum gases of molecules in the rovibronic ground state relies on first associating weakly-bound molecules from quantum-degenerate atomic gases on a Feshbach resonance and then transferring the molecules via several steps of coherent two-photon stimulated Raman adiabatic passage (STIRAP) into the rovibronic ground state. Here, in ultracold samples of Cs2 Feshbach molecules produced out of ultracold samples of Cs atoms, we observe several optical transitions to deeply-bound rovibrational levels of the excited 0(u)+ molecular potentials with high resolution. At least one of these transitions, although rather weak, allows efficient STIRAP transfer into the deeply-bound vibrational level (see text for symbols)v = 73 > of the singlet X1 sigma(g)+ ground state potential, as recently demonstrated (J. G. Danzl, E. Haller, M. Gustavsson, M. J. Mark, R. Hart, N. Bouloufa, O. Dulieu, H. Ritsch, and H.-C. Nägerl, Science, 2008, 321, 1062). From this level, the rovibrational ground state (see text for symbols)v = 0, J = 0 > can be reached with one more transfer step. In total, our results show that coherent ground state transfer for Cs2 is possible using a maximum of two successive two-photon STIRAP processes or one single four-photon STIRAP process.
This paper describes an extension of the familiar coherence effects from atomic systems to the molecular regime. Such effects are inherent in the interaction of multiple laser fields with molecular systems. We have observed Autler–Townes splitting and the AC Stark shift in diatomic Lithium using the continuous wave all-optical triple resonance (AOTR) techniques. By using the Autler–Townes effect, we have partially resolved the magnetic sublevels of a molecular rovibrational level in a Doppler broadened sample, allowing all-optical alignment of the angular momentum in excited states of nonpolar molecules. The Autler–Townes effect in a molecular system extends the rovibrational state selectivity of the AOTR excitation technique to magnetic sublevels. PACS Nos.: 33.40tf, 42.50Hz
In recent years, coherent effects in atomic and molecular systems have been studied extensively, especially in several new classes of effects, such as lasing without inversion (LWI), electromagnetically induced transparency (EIT), coherent population trapping (CPT), AC Stark effect and Autler-Townes (AT) splitting in multilevel systems. The AC stark effect and Autler-Townes splitting in molecules have only been investigated recently. We demonstrate AC stark effect and Autler-Townes (AT) splitting in a lithium molecule using cw multi-photon spectroscopy. The excited upper level of the G1PigG^{1}\\Pi_{g}G1Pig​ is prepared by the optical-optical double resonance (OODR) excitation. The OODR line is split in the presence of a third coupling laser, which couples the upper level to an another intermediate level when the coupling laser is on or near resonance transition. The AT line shape consists of the superposition of ∣MJ∣|M_{J}|∣MJ​∣ components which have been resolved for G1Pig(v=12,J=3,f)G^{1}\\Pi_{g}(v=12, J=3,f)G1Pig​(v=12,J=3,f). We find that the AT splittingis linearly proportional to ∣MJ∣|M_{J}|∣MJ​∣, which allows the excitation of molecules with a selected ∣MJ∣|M_{J}|∣MJ​∣ level. The AC Stark shift of the OODR line is observed when the coupling laser is detuned from the resonance transition.
In this dissertation, three distinct but related experimental works are reported. The first is a study of the highly excited 3^1 Δ_g and 4^1 Δ_g electronic states of 85Rb2. Rovibrational levels of the two electronic states were probed using the high-resolution optical-optical double resonance (OODR) technique by exciting 85Rb2 molecules from thermally populated levels of the X(_ ^1)Σ_g^+ ground state through intermediate levels of the B^1 Π_u electronic state. The (_ ^1)Δ_g resonances induced by the probe laser were observed by detecting laser induced fluorescence (LIF) from nearby, collisionally populated triplet levels to the a^3 Σ_u^+ triplet ground state. The (_ ^1)Δ_g character of the two electronic states was confirmed by showing that the probe transitions to these states abide by (_ ^1)Δ←(_ ^1)Π dipole selection rules and by observing that their lowest rotational level is J = 2. A set of molecular constants and a Rydberg-Klein-Rees (RKR) potential energy curve (PEC) were calculated from the observed term values for each electronic state and compared with ab initio predictions. This is the first observation of (_ ^1)Δ_g states in Rb2.The next results are on the highly excited 6(_ ^3)Π_0g electronic state of the 133Cs2 molecule in an energetic region where very little is known. Rovibrational levels of the excited triplet state were experimentally observed by the perturbation-facilitated-OODR (PFOODR) using a level of the A(_ ^1)Σ_u^+ ~b(_ ^3)Π_u mixed manifold as an intermediate. A progression of P and R branch probe laser resonances were detected by measuring (LIF) to the a(_ ^3)Σ_u^+ state as a function of the probe laser frequency. For select rovibrational levels of the 6(_ ^3)Π_0g state, dispersed fluorescence to the a(_ ^3)Σ_u^+ state and the A(_ ^1)Σ_u^+ ~b(_ ^3)Π_u manifold were also recorded and compared with Frank-Condon factor (FCF) calculations to determine spin multiplicity and vibrational numbering. Term values of the 284 observed rovibrational levels and their quantum numbers were fit to a Dunham expansion to obtain molecular constants, which were in turn used to generate a corresponding RKR-PEC. Comparison to ab initio results led to the assignment of 6(_ ^3)Π_0g . Accurate and high-resolution potential energy curves for the excited states of alkali dimers are crucial for quantum control and cooling experiments relying on techniques such as Stimulated Raman adiabatic passage (STIRAP) and resonantly enhanced multiphoton ionization (REMPI).Lastly, the results of producing state selective molecular angular momentum orientation using dressed states created by a cw optical field are reported. The experiment was carried out with 7Li2 molecules and a combination of left- and right-hand circularly polarized lasers. Our approach exploits the dependence of the Rabi frequency on the quantum number M, which makes it possible to achieve complete M-state selectivity and thus molecular angular momentum orientation relative to laboratory frame space-fixed axes. Using molecules in a (_ ^1)Σ state, orientation of the rotational angular momentum, R ⃑, can be achieved by spectrally resolving the Autler-Townes split M components of the total angular momentum, J ⃑. Results of orienting J ⃑ in (_ ^1)Π state molecules are also discussed. This is the first time complete angular momentum orientation has been achieved in nonpolar molecules and should aid the efforts of stereochemistry, molecular imaging, photodissociation and photoassociation, to name a few.
This thesis reports the creation and trapping of 87RbCs molecules in the absolute ground state with a temperature of 1 uK. We build a tunable narrow-linewidth laser system at 1550 nm and 980 nm, using a single high-finesse optical cavity as a reference for both colours. We use fibre-coupled electro-optic modulators to continuously tune both lasers. These allow a novel measurement of the free spectral range of the cavity to better than 1 part in 10^6. We perform one- and two-photon spectroscopy on 87RbCs Feshbach molecules and identify a suitable intermediate state for transfer to the molecular ground state. We measure the electric dipole moment of the molecular ground state as 1.225(3)(8) D, and demonstrate the highest lab-frame dipole moment of any ultracold molecular system at the time of measurement. We transfer the molecules to the electronic, rovibrational and hyperfine ground state using stimulated Raman adiabatic passage, with 88% efficiency. We measure the transition strengths and excited state linewidth for this transfer route. We develop a model for the transfer which includes the effect of laser linewidth, and find excellent agreement with experimental data. The molecular sample is trapped in an optical dipole potential, and has a lifetime of 0.89(6) s. We reference the STIRAP lasers to a novel design of frequency comb which uses difference frequency generation to cancel the carrier-envelope offset. We use this to measure the binding energy of the molecules as h x 114 268 135.24(4)(3) MHz. To our knowledge, this is the most precise determination of the dissociation energy of a molecule to date. Finally, we report progress toward loading the molecules into a 1D optical lattice at 1064 nm. We develop the tools and methods to characterise a lattice, and demonstrate trapping of Feshbach molecules in both a 1D optical lattice and a harmonic optical potential at 1064 nm.