Coherent coupling between an optical-transition and confined optical mode, when sufficiently strong, gives rise to new modes separated by the vacuum Rabi splitting. Such systems have been investigated for electronic-state transitions, however, only very recently have vibrational transitions been considered. Here, we bring strong polaritonic-coupling in cavities from the visible into the infrared where a new range of static and dynamic vibrational processes await investigation.
First, we experimentally and numerically describe coupling between a Fabry-Perot cavity and carbonyl stretch (~1730 cm 1) in poly-methylmethacrylate. As is requisite for “strong coupling”, the measured vacuum Rabi splitting of 132 cm 1 is much larger than the full width of the cavity (34 cm-1) and the inhomogeneously broadened carbonyl-stretch (24 cm-1). Agreement with classical theories providea evidence that the mixed-states are relatively immune to inhomogeneous broadening. Next, we investigate strong and weak coupling regimes through examination of cavities loaded with varying concentrations of urethane. Rabi splittings increases from 0 to ~104 cm-1 with concentrations from 0-20 vol% and are in excellent agreement to an analytical description using no fitting parameters. Ultra-fast pump-probe measurements reveal transient absorption signals over a frequency range well-separated from the vibrational band as well as modifications of energy relaxation times. Finally, we demonstrate coupling to liquids using the C-O stretching band (~1985 cm-1) of Mo(CO)6 in an aqueous solution.
Opening the field of polaritonic coupling to vibrational species promises to be a rich arena amenable to a wide variety of infrared-active bonds that can be studied statically and dynamically.
Sub-diffractional confinement of light has led to advancements in imaging, metamaterials, nano-manufacturing, plasmonics, and other fields. One potential route to sub-diffractional confinement is via stimulated surface phonon polaritons (SPhPs). SPhPs couple infrared photons with optical phonons and consequently their lifetimes can be longer than surface plasmon polaritons (SPPs), whose lifetimes are dominated by electron scattering events. Thus, materials capable of generating SPhPs are of general interest to study. SPhPs are activated by photons with energies near the Reststrahlen band of semiconductors such as SiC. In this work we examine aspects of carrier dynamics by photo-injecting electrons into the SiC conduction band using a pulsed 355 nm laser and probe the resulting dynamics near the Reststrahlen band using a tunable CO2 laser. The fluence of the pump laser was varied to provide photo-injection levels ranging from ~1x10^17 to 1x10^19 free carriers. Probing the excited-state dynamics near the blue-edge of the Reststrahlen band resulted in complex transient behavior, showing both positive and negative changes in transient reflectance depending on the level of photo-injected carriers and probe energy. Numerical calculations of the SiC reflectance spectra with different doping levels were done to simulate the initial photo-injection level provided by the transient experiment. The computed spectra and the experimentally measured excited spectra for different photo-injection levels were compared and resulted in qualitative agreement.
Broadband, coherent radiation in the optical frequency range is generated using micro-plasma channels in
atmospheric gases in a pump-probe experiment. A micro-plasma medium is created in a gas by a focused intense
femtosecond pump pulse. A picosecond probe pulse then interacts with this micro-plasma channel, producing broad,
coherent sidebands that are associated with luminescence lines and are red- and blue-shifted with respect to the laser
carrier frequency. These sidebands originate from the induced Rabi oscillations between pairs of excited states that
are coupled by the probe pulse. These excited states become populated in the process of plasma cooling. Thus, the
sideband radiation intensity tracks the micro-plasma evolution. The sidebands incorporate Rabi shifts corresponding
to varying value of the electric field magnitude in the probe pulse: this makes them broad and malleable to tuning.
The intensity of the probe beam ~ 1010 W cm-2, creates a maximum sideband shift of > 90 meV from the carrier
frequency, resulting in an effective bandwidth of 200 meV. The sidebands may be effectively controlled by the
intensity and temporal profile of the probe pulse. The giant Rabi shift is both tunable and coherent over a wide range
of frequencies and over a wide range of atomic transitions. The fact that the coherence is observed in a micro plasma
demonstrates that Rabi cycling is possible at high temperature with moderately high laser intensities (1010 W cm-2)
as long as transitions close to the driving frequency (▵ ~ 2% ωc) are available.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.