We study the relationship between the input phase delays and the output mode orders when using a pixel-array structure fed by multiple single-mode waveguides for tunable orbital-angular-momentum (OAM) beam generation. As an emitter of a free-space OAM beam, the designed structure introduces a transformation function that shapes and coherently combines multiple (e.g., four) equal-amplitude inputs, with the
Attosecond photoionization time delays reveal information about the potential energy landscape that an outgoing electron wavepacket probes upon ionization. In this study, we experimentally quantify the dependence of the time delay on the angular momentum of the liberated photoelectrons. For this purpose, we resolved electron quantum-path interference spectra in energy and angle using a two-color attosecond pump–probe photoionization experiment in helium. A fitting procedure of the angle-dependent interference pattern allows us to disentangle the relative phase of all four quantum pathways that are known to contribute to the final photoelectron signal. In particular, we resolve the dependence on angular momentum of the delay of one-photon transitions between continuum states, which is an essential and universal contribution to the total photoionization delay observed in attosecond pump–probe measurements. For such continuum–continuum transitions, we measure a delay between outgoing
- Award ID(s):
- 1912507
- NSF-PAR ID:
- 10132595
- Publisher / Repository:
- Optical Society of America
- Date Published:
- Journal Name:
- Optica
- Volume:
- 7
- Issue:
- 2
- ISSN:
- 2334-2536
- Page Range / eLocation ID:
- Article No. 154
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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th input carrying a phase delay of . The simulation results show that (1) the generated OAM order ℓ is dependent on the relative phase delay ; (2) the transformation function can be tailored by engineering the structure to support different tunable ranges (e.g., , or ); and (3) multiple independent coaxial OAM beams can be generated by simultaneously feeding the structure with multiple independent beams, such that each beam has its own value for the four inputs. Moreover, there is a trade-off between the tunable range and the mode purity, bandwidth, and crosstalk, such that the increase of the tunable range leads to (a) decreased mode purity (from 91% to 75% for ), (b) decreased 3 dB bandwidth of emission efficiency (from 285 nm for to 122 nm for ), and (c) increased crosstalk within the C-band (from to when the tunable range increases from 2 to 4). -
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