Since the discovery, that a tightly focused femtosecond laser beam can induce a highly localized and permanent refractive index change in a wide range of dielectrics, ultrafast laser inscription has found applications in many elds due to its unique 3D and rapid prototyping capabilities. These ultrafast laser inscribed waveguide devices are compact and lightweight as well as inherently robust since the waveguides are embedded within the bulk material. In this presentation we will review our current understanding of ultrafast laser - glass lattice interactions and its application to the fabrication of inherently stable, compact waveguide lasers and astronomical 3D integrated photonic circuits.
Recently we have demonstrated that conventional (free-space) Faraday rotation spectroscopy (FRS) can be successfully transitioned into optical fiber-based sensing architectures using paramagnetic gas-filled hollow-core photonic bandgap fibers (HC-PCFs)1. Our measurements revealed that due to the birefringence properties of the HC-PCFs, behavior of the fiber-optic FRS signals is substantially different compared to free-space FRS systems. Furthermore, magnetic circular dichroism tends to have much higher influence on the FRS signals than in other systems. To explain this behavior we have developed a theoretical model, and shown that close agreement with the experimental data can be achieved. In this paper we focus attention on the detailed explanation and the in-depth discussion of the model and assumptions incorporated within it. This approach can be easily extended to account for parasitic effects that take place in real-world FRS sensor systems such as imperfect polarizers or birefringent gas cell windows.
We report laser-written chip lasers with potential to be a platform planar technology versatile enough to cover the visible through to the mid-infrared spectral region. By femtosecond laser direct-writing a thulium doped fluoride based glass host (ZBLAN), we have demonstrated a 151% quantum efficiency λ=1.9 μm laser with a close to diffraction limited beam quality (M2~ 1.12 ± 0.08) with 225 nm of continuous tunability in a device that can be rapidly fabricated by singlestep optical processing. The 9 mm long planar chip developed for concept demonstration contains fifteen large modearea waveguides that can operate in semi-monolithic or external cavity laser configurations. This chip laser has achieved the highest quantum efficiency from a planar glass waveguide laser. The depressed cladding geometry supports the largest fundamental modes reported for a rare-earth doped waveguide laser thereby favouring high peak-power operation which is demonstrated by achieving 1.9 kW peak-power pulses when Q-switched.
Microstructured optical fibers provide a unique environment for new compact sensing of gases as they offer advantages including long optical pathlengths, strong confinement of high power light and extremely small sample volumes compared to free-space gas sensing architectures. Here we investigate the interaction of a modulated magnetic field with guided light to detect a paramagnetic active gaseous medium within a hollow-core photonic bandgap fiber (HC-PCF). This novel fiber-optic approach to Faraday Rotation Spectroscopy (FRS) demonstrates the detection of molecular oxygen at 762.309 nm with nano-liter detection volume. By using a differential detection scheme for improved sensitivity, guided-mode FRS spectra were recorded for different coupling conditions of the light (i.e., different light polarization angles) and various gas sample pressures. The observed FRS signal amplitudes and shapes are influenced by the structural properties of the fiber, and magneto-optical properties of the gas sample including the magnetic circular birefringence (MCB) and the magnetic circular dichroism (MCD). A theoretical model has been developed to simulate such FRS signals, which are in good agreement with the observed experimental results and provide a first understanding of guided-mode FRS signals and dynamics of the magneto-optical effects inside the optical fiber. The results show that microstructured optical fibers can offer a unique platform for studies concerning the propagation of light in linearly and circularly birefringent media.
We demonstrate the first operation and preliminary characterization of a dual core double-clad fiber laser where the laser
operates in a coaxially doped thulium outer core region and in-turn resonantly pumps a laser with a holmium doped inner
core. The fiber laser is 790nm pumped producing up to 1.5 W near 2.1μm.
We report on the development of a compact, all fibre laser source operating at 1 μm with a linearly polarized (extinction ratio > 20 dB) and very narrow linewidth (12 pm) output. The unique cavity design included a fibre Bragg grating high reflector and output coupler, inscribed via the point-by-point method directly into the active core. A single splice within the cavity between the fibre incorporating the high reflector and the output coupler permitted re-orientation of the stressors at an angle of 90 degrees to each other, which produced a single lasing polarisation. This simple technique removed the need for a more complicated and expensive polarization controller.
This report presents a discussion of the engineering issues and results of high power 2μm Tm3+-doped fibre lasers pumped at 790nm. To date we have achieved up to 85W from such devices with 54% slope efficiency relative to launched pump. More recently, through using Tm3+ concentrations of approximately 4(wt.)% to enhance the cross-relaxation process (3H4,3H6->3F4,3F4) we have demonstrated slope efficiencies of up to 67% relative to launched power. This represented ~170% quantum slope efficiency for the 790nm pumped 2μm laser.
There is currently considerable interest from the military and civil authorities in defences against man portable air defence systems. One such approach utilizes directing in-band modulated mid-infrared lasers at missile seekers to disrupt the missile tracking. The work presented here discusses some of the engineering issues associated with the development of such a laser system. The laser system is based on the MURLIN (Multi-band Research Laser INfrared). A prototype system has been developed based on a highly efficient diode laser pumped Nd: YAG co-planar folded slab laser that is frequency converted by cascaded optical parametric oscillators and an optical parametric amplifier. The water-cooled system produces up to 1.4 W of modulated power which is distributed across 3-lines in the 2-5 mm spectral region. The potential countermeasure utility of this system is enhanced by the single beam multi-line output and capability to directly modulate the pump diodes with a range of waveforms. The follow-on air-cooled version currently under development has recently achieved 8 W of modulated average power at the 1.064 mm pump wavelength. Measured beam quality is twice the diffraction limit.
Using Tm3+-doped double-clad silica fibre we have produced high power, high efficiency 2μm lasers. To date we have achieved a 59% slope efficiency relative to launched pump power using single end pumping and double passing the pump light. By pumping the fibre laser from both ends, we achieved up to 118W peak output power with 54% slope efficiency relative to launched power at 25% duty cycle. The quantum efficiency of this laser was 120% relative to launched pump power, which we attribute to a cross-relaxation process in Tm3+ (3H4,3H6→3F4,3F4). We have also demonstrated fixed wavelength operation of the laser near 1.9μm by using fibre Bragg gratings.
This paper presents a new frequency conversion architecture based on a cascaded KTiPO4 (KTP) and ZnGeP2 (ZGP) optical parametric oscillator (OPO)/optical parametric amplifier (OPA) system. Up to 0.84 W of combined signal and idler output is achieved, which is tunable across the 3.8-4.8 μm spectral region. Incident Nd:YAG pump power is 6.3 W. To achieve efficient low pulse energy conversion, the KTP OPO used a line focus and multiple crystal walk-off compensation. The novel ZGP OPO/OPA configuration efficiently utilizes both of the orthogonally polarized KTP OPO signal and idler beams. The OPA is pumped by combining the 3.8-4.8 μm output from the ZGP OPO with the unused 2.13 μm beam, which is then focused into two ZGP crystals configured as a walk off compensated OPA. Measured beam quality of the OPA signal and idler output has an M2<2, and the residual 2.13μm OPA pump light is also collinear with the mid-IR light.
The development of compact mid-IR sources using frequency- converted diode lasers has been demonstrated to be applicable for the ultra sensitive, selective, and real time detection of many trace gas species in the infrared spectroscopic fingerprint region, which contains virtually all the fundamental vibrational modes of molecules. This development of infrared laser sources has taken advantage of recent significant technological advances of semiconductor diode lasers and solid state lasers, new nonlinear optical materials, optical fiber and novel data acquisition techniques. Such sensors are able to detect molecules at the parts-per-billion level in ambient air using infrared absorption spectroscopy either by monitoring trace gases in an open path or multi-pass cell configuration. Real world applications ranging from urban, industrial, rural emission studies to spacecraft habitat monitoring are described.
A mid-IR gas sensor using difference frequency generation was developed to measure trace levels of biological carbon monoxide (CO). A periodically-poled lithium niobate crystal is pumped by a continuous wave Ti:Sapphire laser and a compact diode pumped Nd:YAG laser operating at 864.86 and 1064.6 nm, respectively. The strong IR transition R(6) at 2169.2 cm-1 is chosen for convenient CO detection without interference from other gas species. Carbon monoxide is collected and flowed into a multipass cell with an effective optical path length of 18.3 m. Using such an experimental arrangement, we detected the generation of CO at levels of 30 ppb during a 30 min period from living vascular smooth muscle cells in basal state.
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