Jerome V. Moloney

Type-II vertical-external-cavity surface-emitting laser with Watt level output powers at 1.2 μm

Semiconductor laser characteristics based on type-II band-aligned quantum well heterostructures for the emission at 1.2 μm are presented. Ten “W”-quantum wells consisting of GaAs/(GaIn)As/Ga(AsSb)/(GaIn)As/GaAs are arranged as resonant periodic gain in a vertical-external-cavity surface-emitting laser. Its structure is analyzed by X-ray diffraction, photoluminescence, and reflectance measurements. The lasers power curves and spectra are investigated. Output powers at Watt level are achieved, with a maximum output power of 4 W. It is confirmed that laser operation only involves the type-II transition. A blue shift of the material gain is observed while the modal gain exhibits a red shift.

Gain in 1320-nm materials: InGaNAs and InGaPAs semiconductor quantum well lasers

Summary form only given. In InGaNAs the replacement of a few percent of the arsenic atoms by nitrogen leads to a bandgap reduction of up to several hundred meV. The strong shrinkage of the bandgap has been explained by anticrossing between the conduction bands of InGaAs and a degenerate and almost k-independent nitrogen band. We compare two structures: a 6-nm In/sub 0.3/Ga/sub 0.7/N/sub 0.02/As/sub 0.98/ quantum well between 30-nm GaAs barriers and AlGaAs cladding layers and an unstrained 6-nm InGaAs quantum well, between lattice matched 30-nm InGaPAs barriers and InP cladding layers. All calculations are for room temperature and TE-polarized light.

Supercontinuum generation and beatnote detection using ultrafast VECSEL seed oscillators

We present preliminary results showing the potential of VECSEL technology for the generation of high power coherent supercontinuum. Among these results, we demonstrate a stable output power of 16 W with a pulse duration of 71 fs and a repetition rate of 1.7 GHz from a VECSEL oscillator and Ytterbium fiber amplifier. This system was used to generate a coherent supercontinuum averaging 3 W of power using a highly nonlinear photonic crystal fiber. In addition, we discuss the possible methods for the detection and stabilization of the carrier offset frequency. The beatnote between a VECSEL seeded supercontinuum and an external CW laser reveals a relatively stable signal, well above the detection noise. A discussion about system design considerations for noise reduction and increased offset frequency stability is also included.

Degradation mechanism of SESAMs under intense ultrashort pulses in modelocked VECSELs

Mode-locked VECSELs using SESAMs are a relatively less complex and cost-effective alternative to state-of-the-art ultrafast lasers based on solid-state or fiber lasers. VECSELs have seen considerable progress in device performance in terms of pulse width and peak power in the recent years. However, it appears that the combination of high power and short pulses can cause some irreversible damage to the SESAM. The degradation mechanism, which can lead to a reduction of the VECSEL output power over time, is not fully understood and deserves to be investigated and alleviated in order to achieve stable mode-locking over long periods of time. It is particularly important for VECSEL systems meant to be commercialized, needing long term operation with a long product lifetime. Here, we investigate the performance and robustness of a SESAM-modelocked VECSEL system under intense pulse intensity excitation. The effect of the degradation on the VECSEL performance is investigated using the SESAM in a VECSEL cavity supporting ultrashort pulses, while the degradation mechanism was investigated by exciting the SESAMs with an external femtosecond laser source. The decay of the photoluminescence (PL) and reflectivity under high excitation was monitored and the damaged samples were further analyzed using a thorough Transmission Electron Microscopy (TEM) analysis. It is found that the major contribution to the degradation is the field intensity and that the compositional damage is confined to the DBR region of the SESAM.

Structure and cavity geometry optimization for ultrashort and high power pulse generation from a VECSEL

Here we present the gain and SESAM structure design strategy employed for the demonstration of ultrashort pulses and we present a comprehensive study outlining the influence of the cavity geometry on the pulse duration and peak power achievable with a state of the art VECSEL and SESAM structure. We will discuss the physical mechanisms limiting the output power with near 100fs pulses and we will compare experimental results obtained with different cavity geometries, including a V-shaped cavity, a multi-fold cavity, and a ring cavity in a colliding pulse modelocking scheme. The experimental results are supported by numerical simulations.

1.2μm emitting VECSEL based on type-II aligned QWs

Since the invention of VECSELs, their great spectral coverage has been demonstrated and emission wavelengths in the range from UV to almost MIR have been achieved. However, in the infrared regime the laser performance is affected by Auger losses which become significant at large quantum defects. In order to reduce the Auger losses and to develop more efficient devices in the IR, type-II aligned QWs have been suggested as alternative gain medium for semiconductor lasers.

Fully Microscopic Studies of Strong-Field Atom Ionization

The interaction of a highly off-resonant light pulse with an atomic gas is modeled fully microscopically. The resulting equations are solved numerically for an atomic model system excited by a strong light pulse.

Seeded optical breakdown of molecular and noble gases

We report experimental results on the dual laser-pulse plasma excitation in various gases at atmospheric pressure. Dilute plasma channels generated through filamentation of ultraintense femtosecond laser pulses in air, argon, and helium are densified through the application of multi-Joule nanosecond heater pulses. Optical breakdown in atomic gases can be achieved for considerably longer delays between femtosecond and nanosecond pulses compared to that in molecular gases. The densification of the seed channel in molecular gases is always accompanied by its fragmentation into discrete bubbles, while in atomic gases the densified channel remains smooth and continuous.

Filamentation of beam-shaped femtosecond laser pulses

When ultra‐intense and ultra‐short optical pulses propagate in transparent dielectrics, the dynamic balance between multiple linear and nonlinear effects results in the generation of laser filaments. These peculiar objects have numerous interesting properties and can be potentially used in a variety of applications from remote sensing to the optical pulse compression down to few optical cycles to guiding lightning discharges away from sensitive sites. Materializing this practical potential is not straightforward owing to the complexity of the physical picture of filamentation. In this paper, we discuss recent experiments on using beam shaping as a means of control over the filament formation and dynamics. Two particular beam shapes that we have investigated so far are Bessel and Airy beams. The diffraction‐free propagation of femtosecond Bessel beams allows for the creation of extended plasma channels in air. These extended filaments can be used for the generation of energetic optical pulses with the duration in the few‐cycle range. In the case of filamentation of femtosecond Airy beams, the self‐bending property of these beams allows for the creation of curved filaments. This is a new regime of the intense laser‐pulse propagation in which the linear self‐bending property of the beam competes against the nonlinear self‐channeling. The bent filaments generated by ultra‐intense Airy beams emit forward‐propagating broadband radiation. Analysis of the spatial and spectral distribution of this emission provides for a valuable tool for analyzing the evolution of the ultra‐intense optical pulse along the optical path.When ultra‐intense and ultra‐short optical pulses propagate in transparent dielectrics, the dynamic balance between multiple linear and nonlinear effects results in the generation of laser filaments. These peculiar objects have numerous interesting properties and can be potentially used in a variety of applications from remote sensing to the optical pulse compression down to few optical cycles to guiding lightning discharges away from sensitive sites. Materializing this practical potential is not straightforward owing to the complexity of the physical picture of filamentation. In this paper, we discuss recent experiments on using beam shaping as a means of control over the filament formation and dynamics. Two particular beam shapes that we have investigated so far are Bessel and Airy beams. The diffraction‐free propagation of femtosecond Bessel beams allows for the creation of extended plasma channels in air. These extended filaments can be used for the generation of energetic optical pulses with the dura...

Short-Length, High-Power Multi-Core Coherently Coupled Fiber Lasers

An all-fiber approach is utilized to phase lock and select the in-phase supermode of compact 19- and 37-core fiber lasers that are a few cm long, aligning-free in operation, and environmentally robust.