Time-Resolved Optical Spectroscopy
BASICS:
Optical properties of the material like reflectivity
and transmissivity depend on the occupancy of the electronic states since
the electrons are able to absorb photons only if empty final states are
available. Therefore by exciting electrons with a short laser pulse one
changes the occupancy of the electronic states by this changing material's
optical properties.
Recent development in the generation of extremely
short (down to 4 fs pulses have been reported) and intense laser pulses
have opened a way to study fast transient phenomena, such as phonon and
electron energy relaxation in solids. A so called pump-probe experiments
have been done where a short and intense laser pulse is used to excite
the electrons and another weaker variably delayed pulse for determining
the temporary change in transmission (reflection).
The relative changes in optical constants are
of the order of 10-5 and are due to fluctuations of the probe
beam intensity (laser noise) impossible to measure directly. Therefore
a special technique called a heterodyne detection (lock-in detection) must
be used in order to eliminate the laser noise.
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Photograph
and scheme of the experimental set-up
used in our laboratory at IJS.
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related papers
(in .pdf format):
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Photoexcited carrier relaxation and
localization in Bi2Sr2Ca1-yYyCu2O8 and YBa2Cu3O7-d: A study by femtosecond
time-resolved spectroscopy, Phys. Rev. B53, 12436 (1996)
-
Evidence for Two-component Superconductivity
in the Femtosecond Optical Response of YBa2Cu3O7-d,
Phys. Rev. Lett. 78, (1997) (Download)
-
I. Mazin: Comment to Evidence
for Two-component Superconductivity in.... , Phys. Rev. Lett. 80,3664,
(1998) (Download)
-
Reply to Comment by I. Mazin, Phys.
Rev. Lett. 80,3665, (1998) (Download)
-
Evidence for polarons and itinerant
carriers in superconductivity from time-resolved optical measurements on
YBa2Cu3O7-d, J. Supercond. (USA),
vol.10, no.4, 337-41, (1997) (Download)
-
Evidence for Two-component Superconductivity
in the Femtosecond Optical and Transient Photoconducting Response of YBa2Cu3O7-d,
Physica C, 282-287, 186-9, (1997) (Download)
-
Analysis of the photoresponse of Y-Ba-Cu-O
thin films on ps to microsecond timescales, Proceedings of EUCAS 1997,
the Third European Conference on Applied Superconductivity, vol.1
p.149-156, (1997) (Download)
-
Divergence of the quasiparticle lifetime
with doping and evidence for preformed pairs below T* in YBa2Cu3O7-d
: Direct measurements by femtosecond time-resolved spectroscopy, Proceedings
of the SNS'97, Cape Cod, to be published in J.Phys. Chem. Sol. (98)
(Download)
To: Spectroscopy Laboratory,
Quantum Optics and Spectroscopy Laboratories
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