Single-Cycle Terawatt Twisted-Light Pulses at Midinfrared Wavelengths above 10 \textmu{}m

Single-Cycle Terawatt Twisted-Light Pulses at Midinfrared Wavelengths above 10 µm

Xing-Long Zhu, Min Chen, Su-Ming Weng, Paul McKenna, Zheng-Ming Sheng, and Jie Zhang

Phys. Rev. Applied 12, 054024 – Published 11 November 2019

Abstract

Twisted-light beams with orbital angular momentum provide an additional degree of freedom in controlling light-matter interactions, which are interesting for fundamental and applied research. Although there are various methods that can produce twisted laser beams at submicrometer or shorter wavelengths, it is still challenging to extend such beams to midinfrared (mid-IR) wavelengths with relativistic intensities. Here, we present a promising scheme to generate such pulses, which are converted through frequency downshift of intense driver optical pulses via a plasma-based photon decelerator. The resulting near-single-cycle vortex pulses cover a broad mid-IR spectral range up to 18 µm with an energy-conversion efficiency of 4.8% (energy approximately 150 mJ) in the wavelength range above 7 µm. These long-wavelength infrared pulses at the terawatt level can be focused to relativistically high intensities, which may offer significant opportunities for high-field physics and ultrafast applications.

Received 8 July 2019
Revised 18 July 2019

DOI:https://doi.org/10.1103/PhysRevApplied.12.054024

Physics Subject Headings (PhySH)

Angular momentum of light Laser-plasma interactions Light-matter interaction Nonlinear optics Optical sources & detectors Optical vortices Ultrafast optics

Infrared techniques

Atomic, Molecular & Optical

Authors & Affiliations

Xing-Long Zhu ^1,2,3, Min Chen ^1,3,*, Su-Ming Weng^1,3, Paul McKenna^2,4, Zheng-Ming Sheng ^{1,2,3,4,5,†}, and Jie Zhang^1,3,6

¹Key Laboratory for Laser Plasmas (MOE), School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China
²SUPA, Department of Physics, University of Strathclyde, Glasgow G4 0NG, United Kingdom
³Collaborative Innovation Center of IFSA, Shanghai Jiao Tong University, Shanghai 200240, China
⁴Cockcroft Institute, Sci-Tech Daresbury, Cheshire WA4 4AD, United Kingdom
⁵Tsung-Dao Lee Institute, Shanghai 200240, China
⁶Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China

^*minchen@sjtu.edu.cn
^†z.sheng@strath.ac.uk

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Vol. 12, Iss. 5 — November 2019

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Figure 1
Schematic of the plasma photon decelerator for producing intense mid-IR vortex pulses. (a) A plasma wake with a bubblelike shape is created during the propagation of an intense laser pulse in an underdense plasma channel. (b) An intense mid-IR few-cycle pulse is generated inside the bubble, behind the drive laser pulse, after a propagation distance of 2 mm, when it undergoes a strong frequency downshift. (c) The density distribution of the plasma channel, where the density is set to $n_{e 0} = n_{0} + Δ n_{0}$ , the red line indicates the background density profile along the x axis with $n_{0} = 3 \times 10^{- 3} n_{c}$ at the plateau, the color map represents the channel depth of $Δ n_{0} = (π r_{e} σ_{0}^{2})^{- 1} (r^{2} / σ_{0}^{2})$ , r is the distance from the channel axis, $r_{e} = e^{2} / m_{e} c^{2}$ is the classical electron radius, $σ_{0} = 20 μ m$ is the laser spot size, and $n_{c} = m_{e} ω_{0}^{2} / 4 π e^{2} = 1.1 \times 10^{21} c m^{- 3}$ is the critical plasma density. $L_{p}$ and $L_{f}$ represent the longitudinal lengths of the density plateau and down ramp, respectively.
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Figure 2
Generation of relativistic mid-IR twisted pulses. (a)–(c) Distributions of the plasma density $(n_{e})$ and transverse electric field $(E_{y})$ in the $ξ$ -y plane, and their longitudinal distributions at the transverse position of $(y, z) = (\sqrt{2} σ_{0} / 2, 0)$ . In (a), the laser pulse front has just reached the end of the density up ramp. In (b), the laser pulse front has reached $x \approx 1595 μ m$ , where the frequency downshift is still relatively small. In (c), the laser pulse front has reached the end of the density down ramp, where the plasma bubble is filled with the mid-IR pulse. The upper insets in (a)–(c) show the transverse slices of $E_{y}$ in the y-z plane, and the green dashed lines plot their corresponding longitudinal positions. Here, the electric field and electron density are normalized to $E_{0} = m_{e} c ω_{0} / e$ and $n_{c}$ , respectively. (d) Spectral distribution of the modulated pulses, where the red line, green line, and blue line correspond to the times in (a)–(c), respectively. The inset shows the temporal waveform of the electric field of the infrared pulse at the central wavelength, $λ_{c} \approx 12 μ m$ . The drive LG laser pulse has a topological charge of $l = 1$ .
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Figure 3
Parameters and phase locking of the twisted mid-IR pulses. (a) Effect of the plasma plateau length, $L_{p}$ , on the optical cycle, energy-conversion efficiency, and electric field amplitude of the output mid-IR pulse, where $Δ L_{p} = L_{p} - L_{p 0}$ is the change of plasma plateau length relative to the initial plateau length $(L_{p 0} = 1650 μ m)$ shown in Fig. 1; all other parameters are unchanged. (b) Effect of the density down-ramp length, $L_{f}$ , on the optical cycle, energy-conversion efficiency, and central wavelength of the output mid-IR pulse, while keeping all other parameters unchanged. (c) Effect of the background plasma density, $n_{0}$ , on the output mid-IR pulse, while keeping $n_{0} L_{p} = 4.95 n_{c} μ m$ fixed, where the drive laser pulse, and the length of density up and down ramps are unchanged. (d) The CEP dependence of the output mid-IR pulse on the drive pulse for the case presented in Fig. 2. The inset plots the waveform of the $λ_{c} \approx 12 μ m$ infrared pulse for three different initial phases ( $ψ_{drive} = 0$ , $π / 2$ , and $π$ ) of the drive laser pulse.
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Figure 4
Conversion from a drive laser pulse with $l = 2$ to twisted mid-IR pulses using a plasma photon decelerator. Distributions of mid-IR pulses in the $ξ$ -y plane (a) and in 3D view (b). Here, the topological charge of the drive laser pulse is changed from $l = 1$ to 2 for the case presented in Fig. 2; all other parameters are unchanged. The insets in (a) present the transverse electric field slices of the drive pulse and the mid-IR pulse in the y-z plane. (c) Spectral distributions of the input drive pulse and the output infrared pulse. The inset plots the temporal waveform of the electric field of the $λ_{c} \approx 10 μ m$ infrared pulse.
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Physical Review Applied

Single-Cycle Terawatt Twisted-Light Pulses at Midinfrared Wavelengths above 10 µm

Xing-Long Zhu, Min Chen, Su-Ming Weng, Paul McKenna, Zheng-Ming Sheng, and Jie Zhang

Phys. Rev. Applied 12, 054024 – Published 11 November 2019

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