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Generation of giant single-cycle pulses of THz light for controlling matter Vitaliy Goryashko 2016 What, Why and How Control of matter with THz light Overview of low-energy collective excitations Switching on and off spin-waves in

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Generation of giant single-cycle pulses of THz light for controlling matter

Vitaliy Goryashko

2016

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What, Why and How

Control of matter with THz light

  • Overview of low-energy collective excitations
  • Switching on and off spin-waves in antiferromagnets
  • THz plasmons in graphene
  • Control of superconducting transport
  • THz dynamics in bacteriorhodopsin

Generation of single-cycle THz pulses

  • Optical rectification
  • Transition THz radiation from e-bunches
  • Half-cycle THz pulses from an undulator

Proposal for a THz Light at Uppsala

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Control of matter with THz light

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Low-energy excitations: D. N. Basov et al., Rev. of Mod. Phys. 2011

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  • direct access to low energy degrees of freedom in complex

matter

  • below optical transitions – no parasitic effects from optical

pump laser pulses

  • low heat deposit
  • field effects directly in the time domain

Beauty of ultra-short THz pulses

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  • easy axis (112)
  • Neel temperature 523 K
  • peak magnetic field of 0.13 T
  • time resolution 8 fs

THz induced magnetization dynamics in NiO

  • =

×

  • T. Kampfrath,

Nature Photonics,

  • vol. 5, 2010
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Dynamics of spins

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Switching on and off magnons

An induced magnetization M(t) manifests itself by the Faraday effect

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Prediction of spin flipping

Effective Hamiltonian Landau-Lifshits- Gilbert eq. of motion Effective magnetic field

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ω = 1087 cm-1, λ = 9200 nm IR s-SNOM image 1 µm (1) near-field at tip apex excites graphene plasmons (2) plasmons are backreflected at graphene edge (3) tip scatteres interfering fields at tip apex (1) (2) (3) Graphene SiC

λ = 10 µm

Tip-enhanced real-space mapping of mid-IR plasmons in graphene (plasmon interferometry)

Courtesy of A. Nikitin

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λ0 = 9.20 µm λ0 = 9.68 µm λ0 = 10.15 µm εSiC = 2.9 εSiC = 2.0 εSiC = 0.7 1 µm Graphene SiC q (cm-1) x 105 TO LO Graphene plasmon dispersion

  • n SiC

Interference fringes, i.e. plasmon wavelengths, increase stronger due to decreasing dielectric value of the SiC substrate εSiC

  • J. Chen et al., Nature 487, 77 (2012)

Spectroscopic mapping reveals plasmon dispersion

Courtesy of A. Nikitin

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Superconducting transport between layers of a cuprate is gated with high-field terahertz pulses, leading to oscillations between superconductive and resistive states, and modulating the dimensionality of superconductivity in the material. Light induced superconductivity

Andrea Cavalleri group

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Bacteriorhodopsin is a light-driven proton pump

Bacteriorhodopsin acts as a proton pump; that is, it captures light energy and uses it to move protons across the membrane out of the cell.[2] The resulting proton gradient is subsequently converted into chemical energy.

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Transformation cycle of bacteriorhodopsin

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Generation of single-cycle THz pulses

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Generation of terahertz pulses by optical rectification

The incoming field E with frequency ω generates a nonlinear polarization P via the second order nonlinear susceptibility.

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Moving charge in a medium 1/

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By tilting the optical pulse front, one achieves coherent build up of a THz wave with a long interaction length.

Phase matching

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Generation of THz pulses through transition radiation

  • Transition radiation is produced by

relativistic charged particles when they cross the interface of two media of different dielectric constants.

  • Since the electric field of the particle is

different in each medium, the particle has to "shake off" photons when it crosses the boundary. = −2 < 0 , = 0 for ≥ 0, = −2 . metallic screen ! " ≈ Δ% & '( 2 log 4 − 1 The energy emitted in the spectral range Δ, reads = 1 1 − &/(&

̅

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  • M. Hoffmann et al.,
  • Vol. 36, No. 23 / OPTICS LETTERS 4473
  • energies up to 100 µJ
  • electric fields up to 1MV/cm
  • a frequency band

from 200 GHz to 100 THz

Single-cycle THz pulses at DESY: 1 MV/cm

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Single-cycle THz pulses at FACET/SLAC: 6 MV/cm 23 GeV beam!

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Proposal for a THz Light Source in Uppsala

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Wish list for intense THz radiation.

Parameter Quasi-half-cycle pulses for time- resolved experiments Narrowband pulses for frequency-resolved experiments Spectral range (THz) 1.5-15 1.5-15 Pulse duration (ps) 0.1-1 1-10 Pulse energy (mJ) 1000 100 Peak electric field (GV/m) 1 0.1 Relative bandwidth FWHM 100% 10% Repetition rate (kHz) 1-100 1-100

+ Polarization control, pump-probe configuration

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The source

  • it covers the spectral range from 5 to 15 THz, exceeding that
  • f laser-based sources;
  • polarization variable from linear to circular or elliptical;
  • tunability of the central frequency and bandwidth;
  • mutli-kilohertz repetition rate;
  • light carrying orbital angular momentum.
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Single-cycle synchrotron radiation

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Single-cycle radiation from a segmented undulator

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Single-cycle radiation from a segmented undulator: cont’d

Magnetic field of segments

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Single-cycle radiation from a segmented undulator

If instead of increasing the distance between the segments I will decrease it, I will recover Takashi’s tapered undulator.

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The source

  • it covers the spectral range from 5 to 15 THz, exceeding that
  • f laser-based sources;
  • polarization variable from linear to circular or elliptical;
  • tunability of the central frequency and bandwidth;
  • mutli-kilohertz repetition rate;
  • light carrying orbital angular momentum.
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Source 1: quasi-half-cycle pulses

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Source 2: multi-cycle pump and single-cycle probe Source 2a Source 2b

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Proposal for a THz light source in Uppsala

Parameter Quasi-half-cycle pulses for time- resolved experiments Narrowband pulses for frequency-resolved experiments Spectral range (THz) 1.5-15 1.5-15 Pulse duration (ps) 0.1-1 1-10 Pulse energy (mJ) 1000 100 Peak electric field (GV/m) 1 0.1 Relative bandwidth FWHM 100% 10% Repetition rate (kHz) 1-100 1-100

+ Polarization control, pump-probe configuration