national high magnetic field laboratory
PULSED FIELD FACILITY
the future
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DETECTORS, SPECTROMETERS & SOURCES
CONTINUOUS SPECTRAL MEASUREMENTS IN PULSED FIELDS
ABSORPTION AND PL SPECTROSCOPY OF HIGHLY-ALIGNED CARBON NANOTUBES
TIME RESOLVED PHOTOLUMINESCENCE IN HIGH B FIELDS
MAGNETIC CIRCULAR DICHROISM & FARADAY ROTATION
OTHER MEASUREMENTS & METHODS
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specialization and methods
Optical
Spectroscopy
NHMFL-PFF
Contact:
Scott Crooker
505-665-7595
crooker@lanl.gov
detectors and spectrometers
• UV-VIS CCD array detector (backthinned, LN2-cooled; Princeton Instruments)
• IR array detector (InGaAs array, LN2-cooled; Princeton Instruments)
• Multichannel-plate PMT and avalanche photodiodes for time-resolved PL
• 300 mm & 500 mm spectrometers (Acton)
• Ti:sapphire (both ultrafast pulsed & CW ring). Frequency doubling available.
• Helium-cadmium (442nm and 325nm)
• CW dye
• variety of laser diode sources (532nm, 405nm, 635nm, 785nm, 1550nm, etc)
• Tungsten-halogen and Xe lamps for broadband white light
• pulsed whitelight generation via photonic crystal fiber
• etc….
sources
continuous spectral measurements in pulsed fields
• Acquire high-res optical spectra at ~1 kHz rate (~1-3 ms/spectra) continuously throughout magnet pulse.
Photoluminescence, absorption, reflection, etc
PL from single ZnMnSe quantum well
wavelength
[Phys Rev. B Rapid Comm. 78, 081402R (2008); Phys. Rev. Lett. 96, 016406 (2006)]
laser
luminescence to spectrometer
& fast, backthinned CCD
0.3-300K
in-situ, thin-film, low-temp polarization optics
0T
60T
T=1.5K
absorption and PL spectroscopy of highly-aligned carbon nanotubes
• Measure absorption and PL from samples of aligned carbon nanotubes
• Aharonov-Bohm splitting and magnetic brightening scale with the magnetic flux threading the nanotube bore.
Voigt geometry; T=1.5T
[Phys Rev. B Rapid Comm. 78, 081402R (2008); Phys. Rev. Lett. 96, 016406 (2006)]
time resolved photoluminescence in high B fields
[Reference: Phys. Rev. Lett. 105, 067403 (2010); J. Phys. Chem. B 109, 15332 (2005)]
An example using time-correlated single photon counting (TCSPC):
• Time-resolved PL from PbSe nanocrystals in fields up to 15 T, temps down to 0.27 K
• Temperature-dependent lifetime indicates fine structure of excitons in these dots
magnetic circular dichroism & Faraday rotation
A method for optically probing magnetic properties in many materials
• e.g., from iron-phthalocyanine films
• e.g., from magnetically-doped semiconductor nanocrystals
λ tunable
light source
RCP/LCP modulator
detector
0-8 Tesla
1.5-300K
[Nature Materials 8, 35 (2009); PRB 86, 014409 (2012)]
other measurements & methods
Imaging spin currents in semiconductors using scanning Kerr-rotation microscopy
[Science 309, 2191 (2005); PRL 94, 236601 (2005); New J. Phys. 9, 347 (2007); PRB Rapid 80, 041305]
We visualize the spin currents resulting from either optical or electrical spin injection.
GaAs
iron
50μm
Fluorescence line narrowing (resonant PL/Raman) at low-T, high-B
[PRB Rapid Comm 96, 241313 (2006); Nature Comm. 2, 280 (2011)]
We use a narrowband, tunable light source to excite at specific energies, and measure the nearly-resonant emission.
0T
33T
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excite
“Spin noise spectroscopy” of electrons and holes in semiconductor materials
[Nature 431, 49 (2004); PRB 79, 035208 (2009)]
[PRL 104, 036601 (2010); PRL 108, 186603 (2012)]
We use an optical magnetometer to “listen” to the intrinsic, random fluctuations of spins in thermal equilibrium. This ‘spin noise’ alone reveals dynamical properties (via fluctuation-dissipation theorem).
