Tantalum pentoxide (Ta2O5) is a promising material for mass-producible, multi-functional, integrated photonics circuits on silicon, exhibiting robust electrical, mechanical and thermal properties, as well as good CMOS compatibility. In addition, Ta2O5 has been reported to demonstrate a non-linear response comparable to that of chalcogenide glass, in the region of 3-6 times larger than that of materials such as silica (SiO2) or silicon nitride (Si3N4). In contrast to Si-based dielectrics, it will accept trivalent ytterbium and erbium dopant ions, opening the possibility of on-chip amplification. The high refractive index of Ta2O5 is consistent with small guided mode cross-section area, and allows the construction of micro-ring resonators. Propagation losses as low as 0.2 dB=cm have been reported. In this paper we describe the design of a planar Ta2O5 waveguides optimised for the generation of coherent continuum with near infrared pulse trains at kW peak powers. The Pulse Repetition Frequency (PRF) of the VECSEL can be tuned to a sub-harmonic of the planar micro-ring and the optical pump power applied to the VECSEL can be adjusted so that mode-matching of the VECSEL pulse train with the micro-ring resonator can be achieved. We shall describe the fabrication of Ta2O5 guiding structures, and the characterisation of their nonlinear and other optical properties. Characterisation with conventional lasers will be used to assess the degree of coherent spectral broadening likely to be achievable using these devices when driven by mode-locked VECSELs operating near the current state-of- art for pulse energy and duration.
XIPE, the X-ray Imaging Polarimetry Explorer, is a mission dedicated to X-ray Astronomy. At the time of
writing XIPE is in a competitive phase A as fourth medium size mission of ESA (M4). It promises to reopen the
polarimetry window in high energy Astrophysics after more than 4 decades thanks to a detector that efficiently
exploits the photoelectric effect and to X-ray optics with large effective area. XIPE uniqueness is time-spectrally-spatially-
resolved X-ray polarimetry as a breakthrough in high energy astrophysics and fundamental physics.
Indeed the payload consists of three Gas Pixel Detectors at the focus of three X-ray optics with a total effective
area larger than one XMM mirror but with a low weight. The payload is compatible with the fairing of the Vega
launcher. XIPE is designed as an observatory for X-ray astronomers with 75 % of the time dedicated to a Guest
Observer competitive program and it is organized as a consortium across Europe with main contributions from
Italy, Germany, Spain, United Kingdom, Poland, Sweden.
We present a VECSEL based on a gain sample design which utilizes only a single-layer dielectric Al2O3 coating for dispersion management. The gain structure generated pulse durations down to 193 fs in combination with a surface-recombination SESAM, with an average power of 400 mW at 1.6 GHz setting a new peak power record for sub-200 fs mode-locked VECSELs. The pulses obtained were, however, 2x transform-limited and a further FROG measurement of a similar laser is presented revealing a linear chirp and cubic spectral phase.
We report a passively mode-locked InGaAs-quantum well VECSEL, emitting a constant pulse train at an average output power of 18 mW and emission wavelength of 1035 nm, with a continuously tunable pulse repetitionfrequency (PRF) between 0.88 - 1.88 GHz. Pulse duration was 230 fs over 80% of that range. Here we propose a technique making use of the demonstrated VECSEL PRF tunability for a resonant frequency-domain pumpprobe spectroscopic technique for acoustic interrogation of nanostructures. Simulation of suitable GHz acoustic resonators to demonstrate this technique is described.
We present reflection z-scan measurements of a quantum well VECSEL gain structure under pumped and unpumped conditions. The implications for the design of mode-locked cavities will be discussed; both in relation to SESAM mode-locked lasers and the possibility of self-mode-locking.
We present a study of the transient onset of lasing and ultrashort pulse formation in a 1-μm InGaAs/GaAs quantum well (QW) vertical-external-cavity surface-emitting laser (VECSEL) that is mode-locked using an intracavity semiconductor saturable absorber mirror. The intra-cavity power build-up transient is observed following modulation of the laser mode in the cavity. Measuring the rise of the frequency-doubled laser output with respect to the fundamental allows determination of mode-locking onset times and pulse-shortening per round trip. A grating monochromator has been used to resolve the optical spectrum of the fundamental intracavity radiation during pulse formation. Combining both measurements we can begin to provide a comprehensive description of pulse formation in VECSELs.
We report our recent advances on using coherent spectral broadening in normal dispersion photonic crystal fiber, followed by subsequent compression using a high efficiency transmission grating compressor to reduce the pulse duration of the pulse train generated by our mode-locked VECSELs from 400 fs, to close to 100 fs, where coherent supercontinuum generation becomes feasible. Using this approach we have, to date, generated pulses of duration 160 fs, and achieved average powers of > 0.5 W from the compressed output.