Photoelectron chiral dichroism induced by lasers without helicity via chiral hole wave-packets

Abstract

Photoelectron circular dichroism (PECD) is a method where randomly oriented chiral molecules are photoionized due to irradiation by circularly-polarized lasers, yielding large chiral signals in the photoelectron momentum distribution. Recently, PECD was explored with polarization-tailored light such as bi-chromatic and non-collinear drivers, which still produces significant chiral signals. Yet, all known PECD configurations to date exhibit non-zero time-local chirality. That is, they are driven by an intrinsically helical light source. Nonetheless, 'chiral' light can also be non-helical if its chirality manifests on longer timescales (e.g. an optical centrifuge). It remains unknown whether PECD can arise from non-helical coherent light. Here we predict that PECD indeed emerges from non-helical light by employing a train of linearly-polarized intense laser pulses with a rotating polarization axis, which are phase-coherent and time-delayed. We find strong PECD in the model chiral molecule CBrClFH under a wide parameter regime that can be optimized up to ~8% by tuning delays between pulses, suggesting quantum interference. We directly show that the physical mechanism for this type of PECD differs from the standard case, relying on a chiral hole attosecond wave-packet evolving in the molecule, induced by the first linear pulse. Our work shows that multiple mechanisms can give rise to PECD on longer timescales and provides a novel approach for ultrafast chirality spectroscopy and coherent chiral wave-packet manipulation.

Figures (5)

• Figure 1: (a) Illustration of laser pulse train set-up and emerging PECD. (b) Laser instantaneous intensity for the pulse train set-up. (c) Lissajous curve for pulse train. Inset shows the temporal evolution of single pulse out of the train. Here each pulse has a peak intensity of $5\cdot10^{13} [W/cm^2]$, the angle between pulse polarizations is $\theta = 120^o$, $\omega$ corresponds to a wavelength of $800nm$, the inter-pulse delay is $T/2$ for both pulses with $T$ the optical cycle, and in each pulse CEP = $\pi$.
• Figure 2: PECD generated in the SAE model by three-pulse train with parameters similar to those in Fig. \ref{['fig:laser']} (a,b) xz and yz planes PECD for $\Delta t$ = $3T$ respectively. (c,d) xz and yz planes PECD for $\Delta t$ = $T/2$ respectively. Inset in (a) shows the employed laser field lissajous curve. (e) Maximal PECD value vs CEP (for $\Delta t=T/2$). (f) Maximal PECD value vs symmetric delay between pulses (for CEP = $\pi$).
• Figure 3: PECD calculated in the SAE model driven by two-pulse train. (a) xy, and (b) yz, PECD plane chiral signals, in similar laser field parameters to those in Fig \ref{['fig:laser']}, except $\theta$ = $90^o$. Inset in (b) shows the employed laser field lissajous curve. (c) Maximum PECD value vs relative angle between pulse polarization ($\theta$).
• Figure 4: PECD calculated within full-TDDFT theory for 3- and 2-pulse trains with similar parameters to Fig \ref{['fig:laser']}. (a) and (b) are xz and yz plane PECD for 3 pulses train respectively; and (c) and (d) are xz and yz plane PECD for 2 pulses train respectively. Insets shows the employed laser fields.
• Figure 5: Orientation-averaged chiral hole state density difference ($\Delta\rho _{R}(\mathbf{r},t) - \Delta\rho _{S}(\mathbf{r},t)$) dynamics in (a) xy molecular plane, (b) xz molecular plane, and (c) yz molecular plane. Generated in the SAE model by one linear pulse with intensity of $5\cdot10^{13} [W/cm^2]$, $\omega$ corresponds to a wavelength of $800nm$ and one optical cycle of the fundamental duration $T$. The total simulation duration is $3T$ with $dt = 218$$[as]$. The data demonstrate clear chiral hole evolution following the first linear pulse that acts as a pump (inducing chiral dynamics in 3D).