T. Tritschler

Lineshape of harmonic generation by metallic nanoparticles and metallic photonic crystal slabs

We study the linear- and nonlinear-optical lineshapes of metal nanoparticles (theory) and metallic photonic crystal slabs (experiment and theory). For metal nanoparticle ensembles, we show analytically and numerically that femtosecond second- or third-harmonic-generation (THG) experiments together with linear extinction measurements generally do not allow to determine the homogeneous linewidth. This is in contrast to claims of previous work in which we identify a technical mistake. For metallic photonic crystal slabs, we introduce a simple classical model of two coupled Lorentz oscillators, corresponding to the plasmon and waveguide modes. This model describes very well the key experimental features of linear optics, particularly the Fano-like lineshapes. The derived nonlinear-optical THG spectra are shown to depend on the underlying source of the optical nonlinearity. We present corresponding THG experiments with metallic photonic crystal slabs. In contrast to previous work, we spectrally resolve the interferometric THG signal, and we additionally obtain a higher temporal resolution by using 5 fs laser pulses. In the THG spectra, the distinct spectral components exhibit strongly different behaviors versus time delay. The measured spectra agree well with the model calculations.

Determining the carrier-envelope offset frequency of 5-fs pulses with extreme nonlinear optics in ZnO

We excite ZnO samples with two-cycle optical pulses directly from a mode-locked oscillator with average powers of several tens of milliwatts. The emitted light reveals peaks at the carrier-envelope offset frequency f(ø) and at 2f(ø) in the radio-frequency spectra. These peaks can still be detected in layers as thin as 350 nm-a step toward determining the carrier-envelope offset phase itself.

Carrier-wave Rabi flopping: role of the carrier-envelope phase

Recently, a dependence of Rabi flopping on the carrier-envelope phase of the exciting laser pulses was predicted theoretically [Phys. Rev. Lett. 89, 127401 (2002)] for excitation of a thin semiconductor film with intense few-cycle pulses. Here, we report corresponding experiments on 50-100-nm thin GaAs films excited with 5-fs pulses. We find a dependence on the carrier-envelope phase arising from the interference of sidebands from the fundamental or the third-harmonic Mollow triplet, respectively, with surface second-harmonic generation.

Variation of the carrier-envelope phase of few-cycle laser pulses owing to the Gouy phase: a solid-state-based measurement.

The carrier-envelope phase of a laser pulse has recently become an important quantity in extreme nonlinear optics. Because of the topological Gouy phase, it changes while the pulse propagates through the focus of a lens. This variation is measured by a simple solid-state-based approach. The experimental results are analyzed by comparison with simple analytical model calculations.

Signatures of carrier-wave Rabi flopping in GaAs

Summary form only given. Illuminating a semiconductor with a constant light intensity can lead to a periodic oscillation of the inversion, a phenomenon which is known as Rabi flopping. Using pulsed excitation, Rabi flopping has been observed on semiconductors and exhibited periods in the range from 100 fs to 1 ps. Hughes (Phys. Rev. Lett. vol. 81, p. 3363, 1998) theoretically investigated the question of what happens when the light intensity becomes so high that the period of one Rabi oscillation becomes comparable with that of only one cycle of light, 2.7 fs for the band edge of GaAs, and predicted a new phenomenon: carrier-wave Rabi flopping. During a carrier-wave Rabi oscillation, the optical polarization becomes strongly distorted, which can lead to a double-peak structure (the Fourier-transform of the Rabi oscillation) in the third-harmonic (3/spl omega/) spectra. This characteristic shape is quite different from the well-known off-resonant third-harmonic generation. Importantly, resonant effects contain information on the dynamics of electronic resonances-potentially on the timescale of a single optical cycle. It is clear that, under these conditions, the usual envelope approximation breaks down, i.e. both the rotating wave approximation (RWA) as well as the slowly varying envelope approximation (SVEA) must not be used. This paper investigates carrier-wave Rabi flopping experimentally.

Nonlinear optical experiments on waveguide plasmon polaritons using 5 fs pulses

We present improved experiments and theoretical modeling of the linear and third-harmonic optical response of particle plasmons coupled to a waveguide mode using 5 fs laser pulses, dispelling misconceptions of previous work by others.

Variation of the carrier-envelope phase of few-cycle laser pulses due to the Gouy phase

A simple solid-state-based approach is used to measure the variation of the carrier-envelope phase in the focus of a lens due to the Gouy phase. The experimental results are compared with analytical model calculations.

The carrier-wave Mollow triplet in experiments on GaAs excited by 5 fs pulses

With intense 5 fs pulses and improved sample design, we observe the carrier-wave Mollow triplet in bulk GaAs. A dependence on the carrier-envelope offset phase is expected.

Carrier-wave Rabi flopping in semiconductors

Publisher Summary This chapter discusses the carrier-wave rabi flopping in semiconductors. If a two-level system is excited by a resonant light field, a periodic oscillation of the inversion can take place. This periodic oscillation between absorption and inversion is known as Rabi oscillation and requires coherence of the two-level system. Carrier-wave Rabi flopping occurs when the Rabi frequency becomes comparable with the light frequency, while maintaining electronic coherence. Exciting the model semiconductor GaAs, which has a band gap period of 2.9 fs, with optical pulses which are both, extremely short (5 fs) and extremely intense (estimated Rabi periods <3 fs), a highly unusual condition can be seen. After reviewing corresponding and recently published experimental spectra around the third harmonic of the band gap, additional data is presented on the transmitted fundamental wave and compared with the theory. The relevance of these results for exploiting coherent effects in semiconductor saturable absorbers for femtosecond mode-locked lasers is discussed. In conclusion, experiments on carrier-wave Rabi flopping have, for the first time, given access to semiconductor material dynamics on a timescale comparable to only one cycle of light.