Generation of High-Lying Vibrational States in Carbon Dioxide through Coherent Ladder Climbing

Mid-infrared laser excitation of molecules into high-lying vibrational states offers a novel route to realize controlled ground-state chemistry. Here we successfully demonstrate vibrational ladder climbing in the antisymmetric stretch of CO2 in the condensed phase by using intense down-chirped mid-infrared pulses. Spectrally resolved pump–probe measurements directly observe excited-state absorptions attributed to vibrational populations up to the v = 9 state, whose corresponding energy of 2.5 eV is 46% of the dissociation energy. By the use of global fitting analysis, important spectroscopic parameters in the high-lying vibrational states, such as transition frequencies and relaxation times, are quantitatively characterized. Remarkably, our analysis shows that 40% of the molecules are excited above the typical activation barriers in the metal-catalyzed CO2 conversions. These results not only demonstrate the promising ability of infrared excitation to produce elevated vibrational states but also represent a significant step toward accelerating CO2 conversions and other chemical processes via mode-specific vibrational excitation

Supplementary document for Broadband background-free vibrational spectroscopy using a mode-locked Cr:ZnS laser - 6072385.pdf

Supplementa

All-Solid-State Optical-Field-Sensitive Detector for Sub-Nanojoule Pulses Using Metal–Insulator Hybrid Nanostructure

We develop an all-solid-state, metal–insulator hybrid device that is capable of detecting an optical field of sub-nanojoule pulses via optical-field-induced tunneling. The tunneling at a gold/aluminum-oxide (Al2O3) interface is driven by an enhanced near-field of a metal–insulator–metal plasmon. Compared to a conventional device with a metal/air interface, we achieve a substantial increase in the tunneling current because of a reduced barrier height, a reduced effective mass of tunneled electrons, an increased plasmonic near-field enhancement, and a denser array of nanoantennas. The device exhibits a remarkable sensitivity to the optical field, which confirms the optical-field-induced tunneling as an emission mechanism. Furthermore, complete encapsulation of the nanoantennas with dielectric materials, coupled with efficient photocurrent generation, improves the durability against optical irradiation

Media 1: Simultaneous separation of polydisperse particles using an asymmetric nonperiodic optical stripe pattern

Originally published in Applied Optics on 10 March 2009 (ao-48-8-1543

Supplementary document for Mode-locked laser oscillation with spectral peaks at molecular rovibrational transition lines - 6131131.pdf

Supplementa

Supplementary document for Broadband dispersion spectroscopy using interferometric phase modulation under background light suppression - 6443558.pdf

Supplemental Documen

Rotationally displaced electric field intensity distribution around square nanoantennas induced by circularly polarized light

An optical field around regular polygon metal nanostructures excited by circularly polarized light can exhibit rotationally displaced intensity distributions. Although this phenomenon has been recognized, its underlying mechanisms has not been sufficiently explained. Herein, finite-difference time-domain simulations and model analyses reveal that the rotationally displaced optical intensity distribution can be generated when each of the linear polarization components that constitute circular polarization excites a superposition of multiple modes. The proposed model reasonably explains the rotationally displaced patterns for a square nanoantenna and other regular-polygon nanoantennas

Frequency-Modulation Mode-Locked Laser with GHz Spectral Width Tunable in the 2-3 um Region

A narrow-bandwidth actively mode-locked laser using a Cr:ZnS gain medium has been successfully demonstrated. A free-space electro-optic phase modulator is employed in the solid-state laser resonator to achieve frequency-modulation (FM) mode-locking, which achieves a narrow spectral width of ~1 GHz and a pulse duration of ~500 ps over a wide tuning range of 1947-2445 nm. The operation frequency of the modulator determines the repetition rate of the mode-locked pulse train and can stabilize it to millihertz-level without any additional feedback loop systems. We also study the theoretical expression of pulse duration and spectral width in a FM mode-locking in a laser cavity that contains considerable group-delay dispersion. The results indicates that larger intracavity dispersion can only stabilize the laser operation by avoiding mode switching, but also narrow the spectral width and increase the pulse duration. The proposed laser features a narrow spectral width at a desired mid-infrared wavelength and a comb-like spectral structure with stabilized longitudinal mode spacing, providing a powerful tool for sensing and control of molecules