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International Journal of Optics

Investigating the Selective Control of Photoassociation of Yb2

Junxia Cheng, Bo Han Tian, Siyu Li, Jia Wang, Shenjiang Wu

Published Sep 4, 2021• 0 citations
Publisher

Abstract

The selective control of photoassociation of Yb2 is investigated in theory. Based on ab initio to rationalize Franck–Condon filtering, the optimal target states of photoassociation have been obtained. The corresponding vibrational transitions from X1Σ+g to the excited state (A1Σu+, B1Πu, C1Σu+, and D1Πu) are v ′ = 23, 50, 55, and 0, respectively. By using quantum wave packet dynamic methods, we calculated the yields with time evaluation for the selected target states. The projections of time-dependent wave functions of initial states on the target vibrational eigenstates reflected the synthetic yields of Yb2. For target A1Σu+, we used Gaussian pulse to make the yield of v ′ = 23 up to 97% at 725 fs. After a laser pulse, the positive chirp promoted the yield of vibrational states to increase, but the negative chirp inhibited its decrease. For the D1Πu state, when laser intensity is 1.0 × 1014 W/cm2, the purity and yield of target state v ′ = 0 reached the maximum at 1350 fs. That is to say, changing the laser parameters and pulse shapes could control the photochemical reaction along our desired direction. These conditions will provide an important reference and suggest a scheme for a feasible photoassociation of further experimental and theoretical research studies. Current study may promote an important step toward the realization of highly accurate quantum manipulation and material synthesis.

DOI
10.1155/2021/6859330

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The selective control of photoassociation of Yb2 is investigated in theory. Based on ab initio to rationalize Franck–Condon filtering, the optimal target states of photoassociation have been obtained. The corresponding vibrational transitions from X1Σ+g to the excited state (A1Σu+, B1Πu, C1Σu+, and D1Πu) are v ′ = 23, 50, 55, and 0, respectively. By using quantum wave packet dynamic methods, we calculated the yields with time evaluation for the selected target states. The projections of time-dependent wave functions of initial states on the target vibrational eigenstates reflected the synthetic yields of Yb2. For target A1Σu+, we used Gaussian pulse to make the yield of v ′ = 23 up to 97% at 725 fs. After a laser pulse, the positive chirp promoted the yield of vibrational states to increase, but the negative chirp inhibited its decrease. For the D1Πu state, when laser intensity is 1.0 × 1014 W/cm2, the purity and yield of target state v ′ = 0 reached the maximum at 1350 fs. That is to say, changing the laser parameters and pulse shapes could control the photochemical reaction along our desired direction. These conditions will provide an important reference and suggest a scheme for a feasible photoassociation of further experimental and theoretical research studies. Current study may promote an important step toward the realization of highly accurate quantum manipulation and material synthesis.
The selective control of photoassociation of Yb2 molecule is investigated in theory. Based on ab initio to rationalize Franck-Condon filtering, the optimal target states of photoassociation have been obtained. That correspond to vibrational transition levels from X1Σ+g to excited state (A1Σu+, B1Πu , C1Σu+, D1Πu) are v’=23, 50, 55, and 0, respectively. The proposed laser drive transitions to target states for association process at wavelength A1Σu+: 464.7nm, B1Πu: 373.1nm, C1Σu+: 361.8nm, D1Πu: 339.1nm are determined. By using quantum wave-packet dynamic methods, we calculated the yields with time evaluation for the selected target states. Interacting with a resonant laser pulse, the projections of time-dependent wave functions of initial states on the target vibrational eigenstates reflected the photoassociation yields of Yb2. For target A1Σu+, using gaussian pulse made the value of v’=23 up to 97% at 725fs. After a laser pulse, that the positive chirp promotes the yield of projection of vibrational states to increase, but the negative chirp inhibits it decrease. For D1Πu state, when laser intensity is 1.0×1014 W/cm2, not only the purity is high but also the yield is high reached 99% of target state v’=0 at 1570fs. That is to say, by changing the laser parameters and pulse shapes, it could much easier control the photochemical along our desired direction. These conditions will provide an important reference and suggest a scheme for a feasible photoassociation for further experimental and theoretical researches.
The photoassociation of alkali metal molecules (Rb2, Cs2, and RbCs) at short range is investigated in theory. Based on ab initio calculations to rationalize Franck–Condon filtering, the target states of photoassociation have been obtained. They correspond to vibrational transition levels from excited state (Rb2: v′{v}{\kern 1pt} 'v′ = 17–21, Cs2: v′{v}{\kern 1pt} 'v′ = 21–25, and RbCs: v′{v}{\kern 1pt} 'v′ = 18–22) to ground state. By using quantum wave-packet dynamic methods, the yields with time evaluation of the selected states are calculated interacting with a resonant laser pulse. Using gaussian pulse leads to the yield of Rb2 up to 82% at 860 fs. After a laser pulse, the positive chirp promotes the yield of vibrational states to increase, but the negative chirp inhibits it. That is to say, by changing the laser parameters and pulse shapes, it is much easier to control the photochemical process along desired direction. For photoassociation of alkali-metal dimers, homonuclear molecules have a better response to laser pulse than heteronuclear molecules. The efficiency of photochemical reaction of homonuclear molecules is much better and the photoassociative yield is much higher. Those conditions will provide an important reference and suggest a scheme for a feasible photoassociation for further experimental and theoretical research.
Abstract The laser synthesis of alkaline earth dimers (Be2, Mg2, Ca2, Sr2, and Ba2) is investigated by theoretical calculation. Photoassociation based on ab initio calculations is rationalized by Franck‐Condon filtering. The optimal target states of photoassociations have been obtained, which are A1∑+u state for Be2, Mg2, and Ca2, and are B1∑+u state for Sr2 and Ba2, corresponding to vibrational transition bands from X1∑+g to excited state are 0‐1, 0‐7, 0‐10, 0‐13, and 0‐3, respectively. The proposed laser drive transitions to target states are also investigated that range from 350 to 740 nm. By using quantum wave‐packet dynamic methods, we calculated the absorption cross sections of photon energy and yields for the selected states of photoassociation. It show that the most sensitive molecules for quantum selective control of photoassociation are Be2 and Ba2 for alkaline earth dimers. These important parameters will provide a feasible scheme for further experimental researches.
Abstract The first step in the coherent control of a photoinduced binary reaction is bond making or photoassociation. We have recently demonstrated coherent control of bond making in multi-photon femtosecond photoassociation of hot magnesium atoms, using linearly chirped pulses (Levin et al 2015 Phys. Rev. Lett. 114 233003 ). The detected yield of photoassociated magnesium dimers was enhanced by positively chirped pulses which is explained theoretically by a combination of purification and chirp-dependent Raman transitions. The yield could be further enhanced by pulse optimization resulting in pulses with an effective linear chirp and a sub-pulse structure, where the latter allows for exploiting vibrational coherences. Here, we systematically explore the efficiency of phase-shaped pulses for the coherent control of bond making, employing a parametrization of the spectral phases in the form of cosine functions. We find up to an order of magnitude enhancement of the yield compared to the unshaped transform-limited pulse. The highly performing pulses all display an overall temporally increasing instantaneous frequency and are composed of several overlapping sub-pulses. The time delay between the first two sub-pulses fits very well the vibrational frequency of the generated intermediate wavepacket. These findings are in agreement with chirp-dependent Raman transitions and exploitation of vibrational dynamics as underlying control mechanisms.
The laser-induced vibrational state-selectivity of product HF in photoassociation reaction H+F→HF is theoretically investigated by using the time-dependent quantum wave packet method. The population transfer process from the continuum state down to the bound vibrational states can be controlled by the driving laser. The effects of laser pulse parameters and the initial momentum of the two collision atoms on the vibrational population of the product HF are discussed in detail. Photodissociation accompanied with the photoassociation process is also described.
We demonstrate coherent control of bond making, a milestone on the way to coherent control of photoinduced bimolecular chemical reactions. In strong-field multiphoton femtosecond photoassociation experiments, we find the yield of detected magnesium dimer molecules to be enhanced for positively chirped pulses and suppressed for negatively chirped pulses. Our ab initio model shows that control is achieved by purification combined with chirp-dependent Raman transitions. Experimental closed-loop phase optimization using a learning algorithm yields an improved pulse that utilizes vibrational coherent dynamics in addition to chirp-dependent Raman transitions. Our results show that coherent control of binary photoreactions is feasible even under thermal conditions.