Molecular Frame Photoelectron Angular Distributions in Polyatomic Molecules from Lab Frame Coherent Rotational Wavepacket Evolution

Molecular Frame Photoelectron Angular Distributions in Polyatomic Molecules from Lab Frame Coherent Rotational Wavepacket Evolution

Margaret Gregory, Paul Hockett, Albert Stolow, Varun Makhija

arXiv:2012.04561, Dec. 2020

The application of a matrix-based reconstruction protocol for obtaining Molecular Frame (MF) photoelectron angular distributions (MFPADs) from laboratory frame (LF) measurements (LFPADs) is explored. Similarly to other recent works on the topic of MF reconstruction, this protocol makes use of time-resolved LF measurements, in which a rotational wavepacket is prepared and probed via photoionization, followed by a numerical reconstruction routine; however, in contrast to other methodologies, the protocol developed herein does not require determination of photoionization matrix elements, and consequently takes a relatively simple numerical form (matrix transform making use of the Moore-Penrose inverse). Significantly, the simplicity allows application of the method to the successful reconstruction of MFPADs for polyatomic molecules. The scheme is demonstrated numerically for two realistic cases, N2 and C2H4. The new technique is expected to be generally applicable for a range of MF reconstruction problems involving photoionization of polyatomic molecules.


 

Photoelectron angular distributions from resonant two-photon ionisation of adiabatically aligned naphthalene and aniline molecules

Photoelectron angular distributions from resonant two-photon ionisation of adiabatically aligned naphthalene and aniline molecules

Molecular Physics, Article: e1836411 | Received 03 Aug 2020, Accepted 06 Oct 2020, Published online: 22 Oct 2020,
https://doi.org/10.1080/00268976.2020.1836411

Photoelectron images have been measured following the ionisation of aligned distributions of gas phase naphthalene and aniline molecules. Alignment in the adiabatic regime was achieved by interaction with a 100 ps infrared laser pulse, with ionisation achieved in a two-photon resonant scheme using a low intensity UV pulse of ∼6 ps duration. The resulting images are found to exhibit anisotropy that increases when the alignment pulse is present, with the aniline PADs peaking along the polarisation vector of the ionising light and the naphthalene PADs developing a characteristic four-lobed structure. Photoelectron angular distributions (PADs) that result from the ionisation of unaligned and fully aligned distributions of molecules are calculated using the ePolyScat ab initio suite and converted into two-dimensional photoelectron images. In the case of naphthalene excellent agreement is observed between experiment and the simulation for the fully aligned distribution, showing that the alignment step allows us to probe the molecular frame, but in the case of aniline it is clear that additional processes occur following the one-photon resonant step.

JCEP seminar videos online

JCEP seminar videos online

The recent JCEP* seminar series is now availble online as a series of videos. This should provide a flavour of current research at NRC and the University of Ottawa, for those interested.

* JCEP = Joint Centre for Extreme Photonics
“The Joint Centre for Extreme Photonics (JCEP) was formed in 2019 as a joint undertaking between the National Research Council (NRC) and the University of Ottawa (uOttawa). It is composed of 12 Fellows: 6 from NRC and 6 from uOttawa. Extreme photonics covers research topics ranging from single-photon sources to intense femtosecond lasers.”

Multivariate Discrimination in Quantum Target Detection

Multivariate Discrimination in Quantum Target Detection

Update July 2020: now published as Appl. Phys. Lett. 117, 044001 (2020); https://doi.org/10.1063/5.0012429

[Submitted on 1 May 2020]

Peter Svihra, Yingwen Zhang, Paul Hockett, Steven Ferrante, Benjamin Sussman, Duncan England, Andrei Nomerotski

We describe a simple multivariate technique of likelihood ratios for improved discrimination of signal and background in multi-dimensional quantum target detection. The technique combines two independent variables, time difference and summed energy, of a photon pair from the spontaneous parametric down-conversion source into an optimal discriminant. The discriminant performance was studied in experimental data and in Monte-Carlo modelling with clear improvement shown compared to previous techniques. As novel detectors become available, we expect this type of multivariate analysis to become increasingly important in multi-dimensional quantum optics.

arXiv:2005.00612

Spectroscopic and Structural Probing of Excited-State Molecular Dynamics with Time-Resolved Photoelectron Spectroscopy and Ultrafast Electron Diffraction

Spectroscopic and Structural Probing of Excited-State Molecular Dynamics with Time-Resolved Photoelectron Spectroscopy and Ultrafast Electron Diffraction

Yusong Liu, Spencer L. Horton, Jie Yang, J. Pedro F. Nunes, Xiaozhe Shen, Thomas J. A. Wolf, Ruaridh Forbes, Chuan Cheng, Bryan Moore, Martin Centurion, Kareem Hegazy, Renkai Li, Ming-Fu Lin, Albert Stolow, Paul Hockett, Tamás Rozgonyi, Philipp Marquetand, Xijie Wang, and Thomas Weinacht
Phys. Rev. X 10, 021016 – Published 22 April 2020

DOI: 10.1103/PhysRevX.10.021016

Pump-probe measurements aim to capture the motion of electrons and nuclei on their natural timescales (femtoseconds to attoseconds) as chemical and physical transformations take place, effectively making “molecular movies” with short light pulses. However, the quantum dynamics of interest are filtered by the coordinate-dependent matrix elements of the chosen experimental observable. Thus, it is only through a combination of experimental measurements and theoretical calculations that one can gain insight into the internal dynamics. Here, we report on a combination of structural (relativistic ultrafast electron diffraction, or UED) and spectroscopic (time-resolved photoelectron spectroscopy, or TRPES) measurements to follow the coupled electronic and nuclear dynamics involved in the internal conversion and photodissociation of the polyatomic molecule, diiodomethane (CH2I2). While UED directly probes the 3D nuclear dynamics, TRPES only serves as an indirect probe of nuclear dynamics via Franck-Condon factors, but it is sensitive to electronic energies and configurations, via Koopmans’ correlations and photoelectron angular distributions. These two measurements are interpreted with trajectory surface hopping calculations, which are capable of simulating the observables for both measurements from the same dynamics calculations. The measurements highlight the nonlocal dynamics captured by different groups of trajectories in the calculations. For the first time, both UED and TRPES are combined with theory capable of calculating the observables in both cases, yielding a direct view of the structural and nonadiabatic dynamics involved.

AMO Open Science forums

AMO Open Science forums

New for 2020 – AMO Open Science forums. It’s early days yet, but hopefully the forums will fill a gap.

“AMO open science forums for students, researchers, academics etc. The aim is to create a place for general scientific discussions and resource sharing, with an open science philosophy, and dissolve usual group/institutional/international boundaries to collaboration.

We also have a companion Slack workspace for IM/real-time discussion duties (non-archival!) and other ephemera – https://amoopenscience.slack.com. This is for forum members only, sign-up here.”

Photoionization dynamics – collected results from ePolyScat

Photoionization dynamics – collected results from ePolyScat

Update Jan 2020: collected results are now online at ePSdata, which supersedes the previous OSF pages. This now includes DOIs for each dataset from Zenodo, and post-processing with the new python version of ePSproc.

An OSF project, collecting photoionization calculations (ePolyScat), and notes, is now available. This will be an ongoing resource for researchers in photoelectron spectroscopy, interferometry and related areas, and is part of our Open Science initiative.

Multidimensional quantum illumination via direct measurement of spectro-temporal correlations

Multidimensional quantum illumination via direct measurement of spectro-temporal correlations

UPDATE May 2020 – now in PRA: Phys. Rev. A 101, 053808 – Published 4 May 2020

Sept. 2019 – New on arXiv

Quantum illumination (QI) is a quantum sensing technique, employing the strong correlation between entangled photon pairs, which is capable of significantly improving sensitivity in remote target detection under noisy background conditions when compared to classical sensing schemes. The amount of enhancement is directly proportional to the number of measurable correlated modes between the photon pairs. QI had been demonstrated using degrees of freedoms such as temporal correlations and photon number correlations, but never a combination of two or more such continuous variables. In this work, we utilize both temporal and spectral correlation of entangled photon pairs in QI. We achieved over an order of magnitude reduction to the background noise when compared to utilizing only temporal modes. This work represents an important step in realizing a practical, real-time QI system. The demonstrated technique will also be of importance in many other quantum sensing applications and quantum communications.

arXiv:1909.09664

Phys. Rev. A 101, 053808 – Published 4 May 2020

DOI: https://doi.org/10.1103/PhysRevA.101.053808

THz-bandwidth all-optical switching of heralded single photons

THz-bandwidth all-optical switching of heralded single photons

Update March 2019 – now in Optics Letters, DOI: 10.1364/OL.44.001427

June 2018 – New on arXiv.

Optically induced ultrafast switching of single photons is demonstrated by rotating the photon polarization via the Kerr effect in a commercially available single mode fiber. A switching efficiency of 97\% is achieved with a 1.7\,ps switching time, and signal-to-noise ratio of 800. Preservation of the quantum state is confirmed by measuring no significant increase in the second-order autocorrelation function g(2)(0). These values are attained with only nanojoule level pump energies that are produced by a laser oscillator with 80\,MHz repetition rate. The results highlight a simple switching device capable of both high-bandwidth operations and preservation of single-photon properties for applications in photonic quantum processing and ultrafast time-gating or switching.

Fibre VUV generation & applications

Fibre VUV generation & applications

Over the last few months (summer 2018) a new project has been shaping up, in collaboration with colleagues from the PCF division (Russell research group) at MPL.  The aim is to develop new ultrafast experiments based on their hollow-core PCFs, which can be used to provide tuneable UV and VUV. This work is part of our larger source development project, and will develop towards applications in photoelectron metrology and quantum optics (amongst others!).

More details to follow, but for now here are a few images of the work in progress…