Er:YGG planar waveguide amplifiers (PWAs) are promising candidates to meet the needs of greenhouse-gas differentialabsorption LIDAR applications. We report pulsed–laser-deposition growth of this doped crystal and net-gain performance (internal gain ~2 dB/cm for 0.7-at.% Er-doping) in a 0.9-cm-long uncoated single-pass PWA. Rapid fabrication is also demonstrated with optimized parameters, where crystal growth rates approaching 20 microns/hour have been realized. We compare Er-doping concentrations ranging from 0.5 at.% - 4 at.%, and report on their spectroscopic properties. Furthermore, we show the ability to tailor the deposited crystal properties, controlling the waveguide and gain characteristics. Finally, we discuss the spectroscopy and potential performance of this relatively unstudied material for PWAs in the eye-safe regime.
Pulsed laser deposition (PLD) is an epitaxial growth technique capable of growing planar layers of crystals with thicknesses up to several 10's of microns. Crystal layers can be grown sequentially without intermediate sample conditioning allowing complicated structures, such as laser-active double-clad designs, to be routinely fabricated. We have recently demonstrated output powers of more than 16W and slope efficiencies of 70% for diode-bar end-pumped planar waveguide oscillators based on PLD Yb:YAG grown on YAG substrates. Here, we present our initial results on varying the growth conditions to tailor the stoichiometry, refractive index, and spectroscopic properties of PLD grown layers. This fine level of control, made possible by this technique, opens the way to bespoke and unique gain media for novel amplifier and lasers designs.
We present our recent advances in the use of pulsed laser deposition (PLD) to fabricate active gain elements for use as amplifiers and laser oscillators. Record output powers exceeding 16 W and slope efficiencies of 70% are reported for optimized epitaxial growth of Yb(7.5%):YAG on to YAG substrates. We show for the first time that the performance of PLD material can meet or even exceed that of materials grown by more established methods such as the Czochralski technique. Details of fabrication, characterization and laser performance are presented in addition to outlining expected future improvements.
An efficient scheme for enhanced second harmonic generation in a nonlinear optical hexagonal microcavity by the combined mechanisms of total internal reflection and quasi-phase-matching is proposed. We demonstrate the operational principle by numerical simulation results showing resonance operation in a suitably designed hexagonal optical microresonator, revealing thus the operating feasibility of the proposed scheme in nonlinear material platforms such as Lithium Niobate. The fabrication of high optical quality hexagonal superstructures by chemical etching of inverted ferroelectric domains in this Lithium Niobate platform suggests a route for successful implementation. Design aspects, optimization issues and characteristics of the proposed device are presented.
The development of organic electronic requires a non contact digital printing process. The European funded e-LIFT project investigated the possibility of using the Laser Induced Forward Transfer (LIFT) technique to address this field of applications. This process has been optimized for the deposition of functional organic and inorganic materials in liquid and solid phase, and a set of polymer dynamic release layer (DRL) has been developed to allow a safe transfer of a large range of thin films. Then, some specific applications related to the development of heterogeneous integration in organic electronics have been addressed. We demonstrated the ability of LIFT process to print thin film of organic semiconductor and to realize Organic Thin Film Transistors (OTFT) with mobilities as high as 4 10-2 cm2.V-1.s-1 and Ion/Ioff ratio of 2.8 105. Polymer Light Emitting Diodes (PLED) have been laser printed by transferring in a single step process a stack of thin films, leading to the fabrication of red, blue green PLEDs with luminance ranging from 145 cd.m-2 to 540 cd.m-2. Then, chemical sensors and biosensors have been fabricated by printing polymers and proteins on Surface Acoustic Wave (SAW) devices. The ability of LIFT to transfer several sensing elements on a same device with high resolution allows improving the selectivity of these sensors and biosensors. Gas sensors based on the deposition of semiconducting oxide (SnO2) and biosensors for the detection of herbicides relying on the printing of proteins have also been realized and their performances overcome those of commercial devices. At last, we successfully laser-printed thermoelectric materials and realized microgenerators for energy harvesting applications.
Many parents or guardians of primary school pupils have little knowledge of science, and many lack confidence in their ability to help their children, though most welcome the chance to do so. We describe our experiences running a series of meetings in the form of coffee sessions at local primary schools, where parents can increase their knowledge and confidence in the science their children study, and engage in simple experiments with their children to apply the knowledge they gain. We discuss how this programme can be instrumental in improving the profile of scientific education and scientific careers for children of a young age.
We present a new light source for parallel Optical Coherence Tomography (OCT) based on multiple waveguides written in Ti:sapphire. Each channel can generate a spectrum of 174 nm bandwidth centered at 772 nm, with an optical power on sample of 30 uW. A system depth resolution of 1.9 um is obtained, which correspond to 1.5 um in tissue.
A method is presented for the covalent attachment of oligonucleotides to silicon (100) surfaces patterned with micron-scale features. UV light exposure of hydrogen-terminated silicon (100) coated with alkenes functionalized with N-hydroxysuccinimide ester groups results in Si-C bonded monolayers. The N-hydroxysuccinimide ester surfaces act as a template for the subsequent covalent attachment of DNA oligonucleotides. In order to create patterns of surface attached DNA oligonucleotides with high density, the surface attachment chemistry has been investigated and optimised. Micron-scale patterning of surfaces was achieved by exposure with UV laser light via a mask. DNA oligonucleotide patterns, with feature sizes of several microns, were reliably produced over large areas. The patterned surfaces were characterised with scanning electron microscopy, epifluorescence microscopy and ellipsometry. Hybridisation with fluorescent label- and gold nanoparticle-conjugates of the complementary oligonucleotide is achieved. The methods offer reliable approaches for the creation of micron-scale motifs of DNA on surfaces.
We report on the fabrication of Ti:sapphire channel waveguides. Such channel waveguides are of interest, e.g., as low-threshold tunable lasers. We investigated several structuring methods including ion beam implantation followed by wet chemical etching strip loading by polyimide spin coating and subsequent laser micro-machining, direct laser ablation or reactive ion etching through laser-structured polyimide contact masks. The later two methods result in ribs having different widths and heights up to ~5 μm. By reactive ion etching we have obtained channel waveguides with strong confinement of the Ti:sapphire fluorescence emission.
We have demonstrated efficient amplification of 830 nm and 1.06 micrometers light in a ring resonator using Rh:BaTiO3. The power oscillating inside the ring exceeded the pump power by up to a factor of 2.3 at 1.06 micrometers . We have also showed that such an efficiently working photorefractive cavity is also sensitive to nanometer changes in its cavity length. We have also observed simultaneous, bi-directional and counterpropagating oscillations in a resonator pumped by a single 647 nm pump beam. The intensity of one oscillation beam was up to two orders of magnitude higher than the intensity of the other oscillation beam.
LiNbO3 and LiTaO3 are commonly used ferroelectric crystal materials. Since the first reports of successful single domain crystal growth in 1965, these materials have found increasing use in optoelectronics, laser systems, Q- switching and frequency conversion, holographic data storage, surface acoustic wave devices, integrated optics and modulator use, and most recently, microwave telecommunications. In single domain format these ferroelectrics are photorefractive, pyroelectric and piezoelectric, and possess usefully large nonlinear optical and electro-optical coefficients. If domain engineering or micron/nano-scale bulk or surface modification is performed however, greater functionality is introduced, leading to additional uses such as phase-matched frequency conversion, grating and photonic structures, and the recently proposed use in MEMS and MOEMS devices. We discuss here a range of techniques for domain engineering and domain selective etching, as well as the use of light in poling and etching modification, and illustrate this potential with several devices that we have constructed by these routes.
Ferroelectric materials such as LiNbO3 and LiTaO3 offer many potential advantages over silicon for MEMS structures and self-actuating miniature devices. These materials possess numerous useful intrinsic properties such as piezoelectricity, pyroelectric and electro-optic coefficients, enabling the construction of micro-scale cantilevers, membranes, tips and switches. So far however, reliable and accurate methods for machining and microstructuring LiNbO3 single crystals have been lacking. We have recently been exploring several such methods, which are sensitive to ferroelectric domain orientation. A sample that has been domain-engineered shows a large difference in etch characteristics: the +z face does not etch at all, whereas the -z face etches normally. Microstructured devices can be fabricated therefore, via spatially selective domain poling followed by etching. The extreme sensitivity of the etch process to domain orientation has enabled us to fabricate ridge waveguides for electro-optic modulator applications, alignment grooves for efficient fibre pig-tailing to LiNbO3 modulators, and micro-cantilevers using a novel technique of contact bonding of dissimilar ferroelectric hosts.
High phase conjugate reflectivities (R > 10,000%) have been achieved through degenerate four-wave mixing in a cw diode-side-pumped Nd:YVO4 amplifier and the interactions have been successfully modelled. This four-wave mixing geometry has subsequently been used in the design of a phase-conjugate resonator operating with a single- longitudinal mode TEMoo near-diffraction limited output of > 7 W, which is capable of correcting for severe intra-cavity phase distortions.
In this work an overview of active planar waveguide systems created by various technologies and especially by method of pulsed laser deposition is given. Parameters of created planar waveguide lasers are summarized. Our experiences with laser deposition and characterization of thin films of Ti:sapphire, Nd:YAG and Nd:YAP are presented. For film deposition a KrF excimer laser was used. Film properties were characterized by XRD, mode spectroscopy, and by study of attenuation and luminescence spectra. Films exhibit waveguiding properties. The waveguide losses as low as 1 dB/cm for Ti:sapphire/sapphire and 0.5 dB/cm for Nd:YAP/(0001)sapphire were measured.
Properties and data of materials for creation of planar waveguide lasers and properties of suitable substrates are summarized. Parameters of published lasers are overviewed. Parameters of active and passive planar waveguides created by method of pulsed laser deposition are described. Results of our experiments of laser deposition of thin Ti:sapphire layers on quartz substrates are presented. Up to 4 waveguiding modes in created layers were observed and attenuation of 6.8 dB/cm was measured.
We investigate the use of combined optical and electrical techniques to control domain formation in ferroelectric SBN, and examine the periodic structures induced by spatially modulating the light intensity through the crystal during the electrical poling process. The role of photoexcited charges in compensating and stabilizing the induced domain structures is summarized, and the importance of thermal effects established. The process of domain re-ordering is shown to be particularly sensitive to temperature changes close to a domain freezing point of SBN, which occurs near room temperature. The resulting light-induced domain re- ordering is assessed using current monitoring during the repoling process, and photorefractive two-beam coupling of the resulting structures.
Thin films of Ti:sapphire were fabricated by KrF laser ablation on (0001) and (1102) sapphire, on (001) quartz and on fused silica substrates from crystalline Ti:sapphire targets. Substrates were heated during the deposition at low temperatures or at high temperatures. Films luminescence, crystallinity, fluorescence lifetime, dopants content, waveguiding and surface morphology of created Ti:sapphire films were studied. Results are presented and discussed.
We present improved experimental results of measurements of ion correlation
effects in a dense plasma. The EXAFS technique was used to observe the short
range order within a dense plasma produced by colliding laser-induced shock
waves. Densities about three times solid density have been measured. An
estimate of the temperature during compression and subsequent heating of
plasma is made using published mcdels and an approximate agreement obtained
with NEDUSA on-dimensional fluid code predictions.