W. R. Garrett

Large spectral shifts of stimulated hyper-Raman scattering: predictions and observations in Xe

Abstract The influence of near-resonant sum or difference frequency-mixing fields on multiphoton excitations can produce large pressure-dependent lineshifts for odd-photon resonances, as recently reported by Garrett et al. [Phys. Rev. Lett. 64 (1990) 1717]. Stimulated hyper-Raman emission from Xe is shown to exhibit similar pressure dependent shifts.

Observations of predicted cooperative shifts in optically pumped stimulated emissions in Xe.

In a recent study Garrett showed that stimulated emissions can be suppressed and shifted under the influence of a wave-mixing interference [Phys. Rev. Lett. 70, 4059 (1993)]. We observe the predicted pressure-dependent frequency shifts in optically pumped stimulated emissions from Xe.

Observation of a critical concentration in laser-induced transparency and multiphoton excitation and ionization in rubidium

We report the behavior of Autler-Townes splitting and production of a four-wave mixing (FWM) field in rubidium in the context of laser-induced transparency. Gain saturation of the FWM and simultaneous suppression of Autler-Townes splitting above a critical concentration are interpreted in terms of the odd-photon destructive interference effect. The results demonstrate that, when multimode lasers are used, odd-photon destructive interference significantly limits the high-efficiency and high-intensity FWM generation promised by early studies of laser-induced transparency.

Multi-photon excitation through a resonant intermediate state : unique separation of coherent and incoherent contributions

We examine two-color three-photon excitation of an optically allowed transition while tuned to an intermediate two-photon resonance in Xe. A wave-mixing interference allows a unique separation of coherent and incoherent contributions to the multi-photon excitation process.

Observation of broadband forward hyper-Raman emission with high intensity focused laser beams

Abstract We show that the well known multiphoton destructive interference, which leads to hyper-Raman gain suppression in the weak pumping regime, no longer occurs under strong pumping conditions. In contrast to the weak pumping case, where no forward hyper-Raman can be observed and strong backward hyper-Raman occurs, forward hyper-Raman emission is found to be much stronger under strong pumping conditions. The emission spectrum acquires new characteristics due to the ac Stark effect introduced by the strong laser field. The frequency spectrum of the forward hyper-Raman is no longer determined by the laser bandwidth, instead a continuum of forward hyper-Raman emission is observed with the width being determined by the peak power density. We will present here a comparison between strong and weak pumping regimes.

Pressure dependence of the ac stark shifts in nitric oxide: resonant multiphoton spectroscopy without space charge

Abstract Measurements of ac Stark shifts and broadening have been made on several multiphoton resonant rotational-vibronic levels in nitric oxide (NO). The levels and laser wavelengths are carefully chosen so that the number of ions produced can be kept low and the complication due to space charge can be avoided. It is found that the ac Stark effects are independent of the pressure.

Effect of the odd-photon destructive interference on laser induced transparency in rubidium

We present evidence that the odd-photon destructive interference plays an important role when laser induced transparency is used to generate a four-wave mixing signal at a frequency corresponding to a resonance transition. We observe that the resonance four-wave mixing works as predicted by the Harris theory until a critical concentration is reached. Well above the critical concentration the four-wave mixing field becomes concentration independent. This destructive interference significantly limits the much anticipated high efficiency nonlinear wave generation promised in early studies on laser induced transparency.

Third harmonic generation and destructive interference with femtosecond laser pulses

With an unfocused femtosecond laser tuned to overlap three-photon resonance with a fine structure doublet, a third harmonic field is predicted which has a bandwidth much narrower than that of the laser. Consequently, this third harmonic field decays slowly with time, lasting as long as several nanoseconds. The population left in the excited states is suppressed by a destructive interference between different excitation pathways.

GAIN SUPPRESSION INVOLVING BOTH STIMULATED RAMAN AND HYPER-RAMAN PHOTONS IN TWO-STEP STIMULATED EMISSIONS

Abstract We show that multiphoton destructive interference leading to gain suppression can be produced even when two different step-wise stimulated emissions, such as stimulated Raman and hyper-Raman emissions, are included in the interference loop.

SHIFTS IN CERTAIN OPTICALLY-PUMPED STIMULATED EMISSIONS UNDER MULTI-BEAM PUMPING

Abstract Recent studies have shown that the gain and the emission frequencies for certain optically-pumped stimulated emissions can be greatly modified during the interval of an excitation pulse through an interference effect. We show a novel means of producing two emission frequencies for a given stimulated transition through the use of bi-directional pump beams and we point to possible analytical applications of the phenomenon.