Marc Jankowski

Reduced models and design principles for half-harmonic generation in synchronously pumped optical parametric oscillators

We develop reduced models that describe half-harmonic generation in a synchronously pumped optical parametric oscillator above threshold, where nonlinearity, dispersion, and group-velocity mismatch are all relevant. These models are based on (1) an eigenmode expansion for low pump powers, (2) a simultonlike sech-pulse ansatz for intermediate powers, and (3) dispersionless box-shaped pulses for high powers. Analytic formulas for pulse compression, degenerate vs nondegenerate operation, and stability are derived and compared to numerical and experimental results.

Cascaded half-harmonic generation of femtosecond frequency combs in the mid-infrared

There is a growing demand for frequency combs in the mid-infrared (mid-IR), also known as the “molecular fingerprint” region of the spectrum. Down-conversion of near-IR frequency combs by half-harmonic generation is a simple way to extend the wavelength coverage of stable frequency combs to this region, and has benefits such as high conversion efficiency and intrinsic phase and frequency locking to the near-IR pump. Here, we report a two-octave down-conversion of a frequency comb around 1 μm through cascaded half-harmonic generation with ∼64% efficiency in the first stage and ∼18% in the second stage. The high conversion efficiency and stable broadband operation indicate the effectiveness and potential of cascaded half-harmonic generation for the realization of intrinsically locked long-wavelength sources, which can be beneficial for numerous applications.

Room temperature polariton lasing from a single GaN nanowire microcavity

The paper demonstrates an ultra-low threshold polariton laser by using a single GaN nanowire as the active medium embedded in a dielectric microcavity. We have also studied the effect of detuning on the lasing characteristics.

Efficient cascaded half-harmonic generation of mid-IR frequency combs (Conference Presentation)

Half-harmonic generation is the reverse of second harmonic generation that happens in optical parametric oscillators (OPOs) at degeneracy. It is an intrinsically phase-locked down-conversion process, which can be used to efficiently transfer well-developed near-IR frequency combs to the mid-IR. We overview recent experimental progress in cascading multiple stages of half-harmonic generation of femtosecond frequency combs starting from a 1-μm pump. We have achieved stable operation with efficiencies as high as ~64%, pulses as short as three optical cycles at 4 μm, and output powers as high as 2.6 W at 2 μm. Our recent numerical and analytical studies of nonlinear dynamics and different operation regimes of femtosecond OPOs indicate a path toward achieving even higher efficiencies and shorter pulses.

19-nJ Five-Cycle Pulses from a 2-μm Degenerate Optical Parametric Oscillator

We report generation of 19-nJ, 35-fs pulses at 2 μm from a degenerate optical parametric oscillator pumped by a 2.6-W 1-μm laser. Near transform-limit operation was achieved with a conversion efficiency of 65%.

Electrically injected polariton lasing from a GaAs-based microcavity under magnetic field

Suppression of relaxation bottleneck and subsequent polariton lasing is observed in a GaAs-based microcavity under the application of a magnetic field. The threshold injection current density is 0.32 A/cm2 at 7 Tesla.

Effect of magnetic field on polariton emission characteristics of a quantum-well microcavity diode

The effect of an applied magnetic field on the polariton emission characteristics of a In0.1Ga0.9As/GaAs multi-quantum well microcavity diode in the strong coupling regime has been investigated. It is observed that the relaxation bottleneck is suppressed due to an enhancement of the polariton-phonon scattering rates in the presence of the magnetic field. A distinct non-linearity is also observed in the light-current characteristics.

InGaN nanowires on silicon: Material characteristics and device applications

Defect-free In(Ga)N nanowires can be grown on Si substrates because of the large surface-to-volume ratio and the radial strain relaxation during growth. These nanostructured materials are therefore uniquely different from commonly used nitride-based heterostructures which are grown on c-plane sapphire and have ∼109 defects per cm2. They can be used to determine intrinsic material properties, to understand limitations in device performance possibly resulting from the defects, and for the design and realization of novel devices.