Generation of picosecond far-infrared pulses using laser-activated semiconductor reflection switches

Hegmann, Frank A.; Sherwin, Mark S.

doi:10.1117/12.262736

“…This is a very different mode of operation to that used in other high-power pulsed EPR spectrometers, where pulse sequences are generated at low power and then amplified. The shutters are high-purity Si wafers with thicknesses carefully polished down to 1/2 wavelength 24,25 . In our 'pulse slicer' (see Fig.…”

mentioning

confidence: 99%

Pulsed electron paramagnetic resonance spectroscopy powered by a free-electron laser

Takahashi

¹

,

Brunel

²

,

Edwards

³

et al. 2012

Nature

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Electron paramagnetic resonance (EPR) spectroscopy interrogates unpaired electron spins in solids and liquids to reveal local structure and dynamics; for example, EPR has elucidated parts of the structure of protein complexes that other techniques in structural biology have not been able to reveal. EPR can also probe the interplay of light and electricity in organic solar cells and light-emitting diodes, and the origin of decoherence in condensed matter, which is of fundamental importance to the development of quantum information processors. Like nuclear magnetic resonance, EPR spectroscopy becomes more powerful at high magnetic fields and frequencies, and with excitation by coherent pulses rather than continuous waves. However, the difficulty of generating sequences of powerful pulses at frequencies above 100 gigahertz has, until now, confined high-power pulsed EPR to magnetic fields of 3.5 teslas and below. Here we demonstrate that one-kilowatt pulses from a free-electron laser can power a pulsed EPR spectrometer at 240 gigahertz (8.5 teslas), providing transformative enhancements over the alternative, a state-of-the-art ∼30-milliwatt solid-state source. Our spectrometer can rotate spin-1/2 electrons through π/2 in only 6 nanoseconds (compared to 300 nanoseconds with the solid-state source). Fourier-transform EPR on nitrogen impurities in diamond demonstrates excitation and detection of EPR lines separated by about 200 megahertz. We measured decoherence times as short as 63 nanoseconds, in a frozen solution of nitroxide free-radicals at temperatures as high as 190 kelvin. Both free-electron lasers and the quasi-optical technology developed for the spectrometer are scalable to frequencies well in excess of one terahertz, opening the way to high-power pulsed EPR spectroscopy up to the highest static magnetic fields currently available.

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“…This is a very different mode of operation than is used in other high-power pulsed EPR spectrometers, where pulse sequences are generated at low power and then amplified. The shutters are high-purity Si wafers with thicknesses carefully polished down to 1/2 wavelength [28,29]. In our "pulse slicer" (see Fig.…”

mentioning

confidence: 99%

Free-Electron Laser-Powered Electron Paramagnetic Resonance Spectroscopy

Takahashi,

Brunel,

Edwards

et al. 2012

Preprint

0

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Electron paramagnetic resonance (EPR) spectroscopy interrogates unpaired electron spins in solids and liquids to reveal local structure and dynamics; for example, EPR has elucidated parts of the structure of protein complexes that have resisted all other techniques in structural biology [1][2][3][4][5]. EPR can also probe the interplay of light and electricity in organic solar cells [6-8] and lightemitting diodes [9], and the origin of decoherence in condensed matter, which is of fundamental importance to the development of quantum information processors [10][11][12][13][14]. Like nuclear magnetic resonance (NMR), EPR spectroscopy becomes more powerful at high magnetic fields and frequencies, and with excitation by coherent pulses rather than continuous waves. However, the difficulty of generating sequences of powerful pulses at frequencies above 100 GHz has, until now, confined high-power pulsed EPR to magnetic fields of 3.5 T and below. Here we demonstrate that ∼1 kW pulses from a free-electron laser (FEL) can power a pulsed EPR spectrometer at 240 GHz

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“…The short pulses are extracted from the high-intensity longpulse output of the UCSB FEL with laser-activated semiconductor switches. 15,16 The switches are manufactured from silicon and are activated by illumination with nearinfrared radiation across the band gap, which generates a reflecting electron-hole plasma. 17 Step-function-like activation of the switches is obtained with a very short (∼150 fs), intense (>1 mJ per switch) near-infrared pulse.…”

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confidence: 99%

Verification of polarization selection rules and implementation of selective coherent manipulations of hydrogenic transitions inn-GaAs

Doty

¹

,

King

²

,

Sherwin

³

et al. 2005

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Electrons bound to shallow donors in GaAs have orbital energy levels analogous to those of the hydrogen atom. The polarization selection rules for optical transitions between the states analogous to the 1s and 2p states of hydrogen in a magnetic field are verified using Terahertz (THz) radiation from the UCSB Free Electron Laser. A polarization-selective coherent manipulation of the quantum states is demonstrated and the relevance to quantum information processing schemes is discussed.In recent years there has been great interest in low dimensional semiconductors, motivated in large part by the potential to implement quantum information processing 1,2,3 in a solid-state system 4,5,6 . The development of methods for selectively addressing and coherently manipulating such quantum systems is essential to a successful implementation of any quantum information scheme. In this work we describe verification of the selection rules for orbital transitions of electrons bound to shallow donors in GaAs and implementation of selective coherent manipulations.The energy levels of shallow donor-bound electrons can be described by the Coulomb interaction between the electron and the positive charge at the donor site, modified by the effective mass of the electron (0.0665 m e ) and the dielectric constant of the material (12.56) 7,8 . This leads to electron energy levels analogous to those of the hydrogen atom, with a small correction for the actual donor species, called the central cell correction (0.110 meV for S donor) 9 . The orbital transitions are in the TeraHertz (THz) frequency regime (a few meV). In the presence of a magnetic field, additional free electron states arise, forming a continuum above each Landau level 8 . The hydrogenic states can be labelled with the usual notation: 1s, 2p + , 2p − , etc.The energy of the hydrogenic states can be tuned with an applied magnetic field to bring orbital transitions into resonance with fixed frequencies of radiation. Klaassen, et al. 8 and Stillman, et al. 10 , have used this technique to perform spectroscopy experiments. To aid in identifying excited states, they have assumed that transitions are governed by the usual hydrogen atom dipole selection rules. However, these experiments have not included control of the polarization state of the THz beam, and to our knowledge no work has yet verified that the hydrogen selection rules remain valid for hydrogenic donors in a semiconductor.The hydrogen selection rules require a σ + -polarized photon to conserve angular momentum and excite the 1s to 2p + transition; σ − -polarization is required for 1s to 2p − . Since the electron effective mass in GaAs is isotropic, the selection rules for the bare hydrogen atom might be expected to hold. However, symmetry in a semiconductor can easily be lost. In quantum dots, for example, elongation of the dot along specific crystal planes can break the dot symmetry and mix the polarization eigenstates of excitons 11 . In this work, we first verify the selection rules for the 1s to 2p ± transitions ...

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Generation of picosecond far-infrared pulses using laser-activated semiconductor reflection switches

Cited by 17 publications

References 33 publications

Pulsed electron paramagnetic resonance spectroscopy powered by a free-electron laser

Pulsed electron paramagnetic resonance spectroscopy powered by a free-electron laser

Free-Electron Laser-Powered Electron Paramagnetic Resonance Spectroscopy

Verification of polarization selection rules and implementation of selective coherent manipulations of hydrogenic transitions inn-GaAs

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