Photodissociation of ozone following absorption of biologically harmful solar ultraviolet radiation is the key mechanism for the life protecting properties of the atmospheric ozone layer. Even though ozone photolysis is described successfully by post-Hartree-Fock theory, it has evaded direct experimental access so far, due to the unavailability of intense ultrashort deep ultraviolet radiation sources. The rapidity of ozone photolysis with predicted values of a few tens of femtoseconds renders both ultrashort pump and probe pulses indispensable to capture this manifestation of ultrafast chemistry. Here, we present the observation of femtosecond time-scale electronic and nuclear dynamics of ozone triggered by \ensuremath{\sim}10-fs, \ensuremath{\sim}2-\textmu{}J deep ultraviolet pulses and, in contrast to conventional attochemistry experiments, probed by extreme ultraviolet isolated pulses. An electronic wave packet is first created. We follow the splitting of the excited B-state related nuclear wave packet into a path leading to molecular fragmentation and an oscillating path, revolving around the Franck-Condon point with 22-fs wave-packet revival time. Full quantum-mechanical ab initio multiconfigurational time-dependent Hartree simulations support this interpretation.

Laser frequency combs, sources with a spectrum consisting of hundred thousands evenly spaced narrow lines, have an exhilarating potential for new approaches to molecular spectroscopy and sensing in the mid-infrared region. The generation of such broadband coherent sources is presently under active exploration. Technical challenges have slowed down such developments. Identifying a versatile highly nonlinear medium for significantly broadening a mid-infrared comb spectrum remains challenging. Here we take a different approach to spectral broadening of mid-infrared frequency combs and investigate CMOS-compatible highly nonlinear dispersion-engineered silicon nanophotonic waveguides on a silicon-on-insulator chip. We record octave-spanning (1,500-3,300 nm) spectra with a coupled input pulse energy as low as 16 pJ. We demonstrate phase-coherent comb spectra broadened on a room-temperature-operating CMOS-compatible chip.

With the help of the strong nonlinear optical response in silicon nanophotonic wire waveguides complex sources and devices can be integrated on a chip. We demonstrate mid-infrared wavelength translators and frequency combs Furthermore, we open up the possibility for the integration of nonlinear optical functions at telecom wavelengths by exploiting more exotic nonlinear interactions in silicon waveguides as well as new waveguide platforms.

Coherent anti-Stokes Raman spectroscopy is achieved on microsecond time scale with two frequency combs and a heterodyne detection with a local oscillator. The vibrational transitions reach a signal-to-noise ratio of 1600 with linear concentration dependence.

We report a few-cycle, broadband, singly-resonant optical parametric oscillator (OPO) for the mid-infrared based on MgO-doped periodically-poled LiNbO3 (MgO:PPLN), synchronously pumped by a 20-fs Ti:sapphire laser. By using crystal interaction lengths as short as 250 um, and careful dispersion management of input pump pulses and the OPO resonator, near-transform-limited, few-cycle idler pulses tunable across the mid-infrared have been generated, with as few as 3.7 optical cycles at 2682 nm. The OPO can be continuously tuned over 2179-3732 nm by cavity delay tuning, providing up to 33 mW of output power at 3723 nm. The idler spectra exhibit stable broadband profiles with bandwidths spaning over 422 nm (FWHM) recorded at 3732 nm. We investigate the effect of crystal length on spectral bandwidth and pulse duration at a fixed wavelength, confirming near-transform-limited idler pulses for all grating interaction lengths. By locking the repetition frequency of the pump laser to a radio-frequency reference, and without active stabilization of the OPO cavity length, an idler power stability better than 1.6% rms over >2.75 hours is obtained when operating at maximum output power, in excellent spatial beam quality with TEM00 mode profile.

The invention of the optical frequency comb technique has revolutionized the field of precision spectroscopy, providing a way to measure the absolute frequency of any optical transition. Since, frequency combs have become common equipment for frequency metrology. In the last decade, novel applications for the optical frequency comb have been demonstrated beyond its original purpose. Broadband molecular spectroscopy is one of those. One such technique of molecular spectroscopy with frequency combs, dual-comb Fourier transform spectroscopy provides short measurement times with resolution and accuracy. Two laser frequency combs with slightly different repetition frequencies generate pairs of pulses with a linearly-scanned delay between pulses in a pair. The system without moving parts mimics a fast scanning Fourier transform interferometer. The measurement speed may be several orders of magnitude faster than that of a Michelson-based Fourier transform spectrometer, which opens up new opportunities for broadband molecular spectroscopy. Recently, dual-comb spectroscopy has been extended to nonlinear phenomena. A broadband Raman spectrum of molecular fingerprints may be measured within a few tens of microseconds with coherent Raman dual-comb spectroscopy. Raster scanning the sample leads to hyperspectral images. This rapid and broadband label-free vibrational spectroscopy and imaging technique might provide new diagnostic methods in a variety of scientific and industrial fields.

We report a broadband mid-IR femtosecond OPO tunable across 2179-3732 nm, pumped by 20-fs pulses at 790 nm, generating idler pulses of 4.3 optical cycles (33 fs) at 2282 nm, with high stability and beam-quality.

A mid-infrared octave spanning supercontinuum is generated in a silicon Photonic wire. The supercontinuum extends over more than an octave, spanning from 1500 nm up to 3300 nm when the photonic wire is pumped with by 70 long pulses having an energy of 16 pJ and centered at 2290 nm. By beating the generated supercontinuum on a photodetector with a narrow line width light source the phase coherence of the supercontinuum is verified.

We demonstrate a novel technique of coherent Raman spectroscopy with a femtosecond laser. We apply to a molecular sample a sequence of pairs of ultrashort excitation and probe pulses, with a linearly increasing time delay between the two pulses from one pair to the next. We measure, as a function of the delay, the intensity modulation in the signal resulting from the differential detection of the Stokes and anti-Stokes radiations generated at the sample. The Fourier transform of such time-domain signal reveals the spectrum of the excited vibrational Raman transitions. The experimental proof-of-principle demonstrates high resolution, broad spectral span and suppression of the non-resonant background, as well as sensitivity enhancement due to the differential detection.

Striking field-induced changes in the absorption near the Si L-edge of SiO2 exposed to a near-infrared laser field of several V/Å delivered by a few-cycle pulse are observed with sub-100 attosecond extreme ultraviolet pulses by means of attosecond transient absorption.

Nonlinear coherent Raman scattering with ultra-short pulse lasers has opened up new opportunities for nonintrusive three-dimensional label-free chemical sensing. A single ultrashort pulse laser, combined to a pulse shaper or a Michelson interferometer, allows for multiplex measurements. However, measuring a broad spectral bandwidth spectrum at high resolution within a very short acquisition time still remains a challenge. Recently dual-comb spectroscopy, which features such characteristics for linear absorption, been extended to nonlinear spectroscopy in a proof-of-principle experiment based on stimulated Raman scattering.

We present a new technique of non-linear dual-comb spectroscopy for the measurement of coherent Stokes and anti-Stokes Raman spectra of fundamental vibrational transitions. Ultra-rapid acquisition times, high-resolution, broad-spectral-span are the main characteristics of our experiments.

Ultra-rapid coherent Stokes and anti-Stokes Raman spectroscopy with two laser frequency combs is demonstrated. Spectra and hyperspectral images are measured over a span of 1200 cm-1 at 4 cm-1 resolution within 15 microseconds.

Ultra-rapid coherent anti-Stokes Raman spectroscopy with two laser frequency combs is demonstrated. Hyperspectral images are acquired over a spectral bandwidth of 1200 cm(-1) with a resolution of 10 cm(-1) at a rate of 50 pixels/s.

Advances in optical spectroscopy and microscopy have had a profound impact throughout the physical, chemical and biological sciences. One example is coherent Raman spectroscopy, a versatile technique interrogating vibrational transitions in molecules. It offers high spatial resolution and three-dimensional sectioning capabilities that make it a label-free tool for the non-destructive and chemically selective probing of complex systems. Indeed, single-colour Raman bands have been imaged in biological tissue at video rates by using ultra-short-pulse lasers. However, identifying multiple, and possibly unknown, molecules requires broad spectral bandwidth and high resolution. Moderate spectral spans combined with high-speed acquisition are now within reach using multichannel detection or frequency-swept laser beams. Laser frequency combs are finding increasing use for broadband molecular linear absorption spectroscopy. Here we show, by exploring their potential for nonlinear spectroscopy, that they can be harnessed for coherent anti-Stokes Raman spectroscopy and spectro-imaging. The method uses two combs and can simultaneously measure, on the microsecond timescale, all spectral elements over a wide bandwidth and with high resolution on a single photodetector. Although the overall measurement time in our proof-of-principle experiments is limited by the waiting times between successive spectral acquisitions, this limitation can be overcome with further system development. We therefore expect that our approach of using laser frequency combs will not only enable new applications for nonlinear microscopy but also benefit other nonlinear spectroscopic techniques.

This work reports on the attosecond real-time observation of the electron processes [1] underlying the ability of ultrastrong few-cycle laser pulses to turn a dielectric solid from an insulating into a conducting state [2].

The ultrafast reversibility of changes to the electronic structure and electric polarizability of a dielectric with the electric field of a laser pulse, demonstrated here, offers the potential for petahertz-bandwidth optical signal manipulation.

The interaction of a few-cycle laser pulse with a metal-dielectric nanostructure creates measurable electric currents. We show that the time scale of the process is sufficiently fast to sample oscillations at visible light frequencies.

The conductivity of a dielectric is reversibly increased by several orders of magnitude on a femtosecond timescale by exploiting the instantaneous electric field of intense few-cycle near-infrared laser pulses leading to measurable ultrafast electric currents.