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Miniature lasers producing ultrashort phase-coherent pulses at high repetition rates by stable mode-locking in ambient conditions can offer unique capabilities in various applications, spanning from microwave photonics to telecom and biological imaging techniques. Here, the operation of graphene mode-locked lasers based on channel waveguides written by femtosecond and picosecond laser pulses in Ti:sapphire crystals is demonstrated. Trains of pulses of 41.4-fs duration at a 21.25-GHz repetition rate were generated by capitalizing on the formation of solitons in their monolithic resonators through Gires–Tournois interferometers. The latter, allow for effective pulse shaping via tuning of the intracavity group delay dispersion while simultaneously enabling ultralow laser operating thresholds. A number of features of these sources, including their high-brightness and broad bandwidth, are essential ingredients for achieving high longitudinal resolution and sensitivity, which are the primary performance metrics of the Fourier domain/spectral domain variant of optical coherence tomography systems. A further doubling of the laser repetition rate to 42.5 GHz was achieved by coherent pulse interleaving in optical fiber technology, thereby underlining the potential of the Ti:sapphire waveguide lasers to produce highly stable, wide-spaced combs of phase-coherent optical frequency lines.

We report on the optical-gain properties of channel waveguides patterned into lattice-matched KGdxLuyEr1-x-y(WO4)2 layers grown onto undoped KY(WO4)2 substrates by liquid phase epitaxy. A systematic investigation of gain is performed for five different Er3+ concentrations in the range of 0.75 to 10at.% and different pump powers and signal wavelengths. In pump-probe-beam experiments, relative internal gain, i.e., signal enhancement minus absorption loss of light propagating in the channel waveguide, is experimentally demonstrated, with a maximum value of 12 ± 5 dB/cm for signals at the peak-emission wavelength of 1534.7 nm.

The field of optically pumped planar waveguide lasers has seen a rapid development over the last two decades driven by the requirements of a range of applications. This sustained research effort has led to the demonstration of a large variety of miniature highly efficient laser sources by combining different gain media and resonator geometries. One of the most attractive features of waveguide lasers is the broad range of regimes that they can operate, spanning from continuous wave and single frequency through to the generation of femtosecond pulses. Furthermore, their technology has experienced considerable advances to provide increased output power levels, deriving benefits from the relative immunity from the heat generated in the gain medium during laser operation and the use of cladding-pumped architectures. This second part of the review on optically pumped planar waveguide lasers provides a snapshot of the state-of-the-art research in this field in terms of gain materials, laser system designs, and as well as a perspective on the status of their application as real devices in various research areas.

Integration of multiple functions on an optical micro-chip is going to revolutionize the exploitation of optics for various applications such as communication, optical sensing, and biomedicine. One of the enabling functions is amplification at 1.5 μm [1]. Rare-earth-doped amplifiers typically deliver a net gain per unit length of only a few dB/cm [2]. In spiral-shaped channel waveguides a total internal net gain of 20 dB was demonstrated [3].

We report the spectroscopy of crystalline waveguide amplifiers operating in the telecom C-band. Thin films of erbiumdoped gadolinium lutetium potassium double tungstate, KGdxLuyEr1-x-y (WO4)2, are grown by liquid- phase epitaxy onto undoped potassium yttrium double tungstate (KYW) substrates and micro-structured by Ar+- beam etching. Channel waveguides with erbium concentrations between 0.45–6.35 × 1020 cm-3 are characterized. The transition cross-sections of interest are estimated. The effect of energy-transfer up-conversion (ETU) is experimentally investigated. Microscopic and macroscopic ETU parameters are extracted from a simultaneous analysis of 20 decay curves of luminescence on the transition 4I13/2 → 4I13/2. The correlation between ETU and the doping concentration is studied. Pump excited-state absorption (ESA) on the transition 4I11/2 → 4F7/2 is investigated via a direct ESA measurement using a double-modulation pump-probe technique. The effect of ESA is studied for different pump wavelengths. The pump wavelength of 984.5 nm is found to be favorable for the complete range of erbium concentrations.

Single-crystalline KY1-x-y-zGdxLuyYbz(WO4)2 layers are grown onto undoped KY(WO4)2 substrates by liquid-phase epitaxy. The purpose of co-doping the KY(WO4)2 layer with suitable fractions of Gd3+ and Lu3+ is to achieve lattice-matched layers that allow us to engineer a high refractive-index contrast between waveguiding layer and substrate for obtaining tight optical mode confinement and simultaneously accommodate a large range of Yb3+ doping concentrations by replacing Lu3+ ions of similar ionic radius for a variety of optical amplifier or laser applications. Crack-free layers, up to a maximum lattice mismatch of ~0.08 %, are grown with systematic variations of Y3+, Gd3+, Lu3+, and Yb3+ concentrations, their refractive indices are measured at several wavelengths, and Sellmeier dispersion curves are derived. The influence of co-doping on the spectroscopy of Yb3+ is investigated. As evidenced by the experimental results, the lattice constants, refractive indices, and transition cross-sections of Yb3+ in these co-doped layers can be approximated with good accuracy by weighted averages of data from the pure compounds. The obtained information is exploited to fabricate a twofold refractive-index-engineered sample consisting of a highly Yb3+-doped tapered channel waveguide embedded in a passive planar waveguide, and a cladding-side-pumped channel waveguide laser is demonstrated.

High-quality crystalline $KY(WO_4)_2:Yb^{3+}$ layers codoped with large concentrations of optically inert Gd3+ and Lu3+ ions were grown by liquid phase epitaxy. Continuous-wave laser operation in a planar waveguide configuration was observed at 1025 nm. For 23% output coupling, a maximum output power of 195 mW was obtained; a slope efficiency of 82.3% was derived, which to the best of our knowledge is the highest value yet reported for a planar waveguide laser to date. For 1.7% output coupling, a laser threshold as low as 18 mW of absorbed pump power was achieved, which is largely due to the enhanced refractive index contrast of ~$7.5\times 10^{-3}$ between the active layer and the undoped $KY(WO_4)_2$ substrate attained by the co-doping, leading to well-confined pump and laser modes

Highly reflective volume Bragg gratings (R∼80%) were written in Ti:sapphire planar and channel waveguides fabricated via pulsed-laser deposition (PLD) by exposure to UV (266 nm) femtosecond laser irradiation through suitable phase masks. Large photo-induced refractive index modulations of up to ∼1×10−2 were observed, which were completely reversible at temperatures of ∼100°C. The dependence of the refractive index modulation on intensity suggests that the mechanism for grating inscription is an one-photon absorption process. Generation of gratings may result from a charge transfer process between the Ti3+ and Ti4+ ions and/or transient localized structural re-arrangements.

A potassium double tungstate layer with the composition KY0.40Gd0.29Lu0.23Tm0.08(WO4)2 was grown onto a pure KY(WO4)2 substrate by liquid-phase epitaxy, microstructured by standard lithography and Ar-ion etching, and overgrown by a pure KY(WO4)2 layer. The end-facets were polished. Laser experiments were performed on these buried, ridge-type channel waveguides in a resonator with one butt-coupled mirror and Fresnel reflection from the other end-facet, resulting in a high output-coupling degree of 89%, compared to intrinsic round-trip losses of only 2%. By pumping with a Ti:Sapphire laser at 794 nm, 1.6 W of output power at 1.84 μm with a maximum slope efficiency of ~80% was obtained. To the best of our knowledge, this result represents the most efficient 2-μm channel waveguide laser to date. We determined the optimum Tm3+ concentration in double tungstate channel waveguides to be at least 8at.% for efficient lasing. The theoretical limit of the slope efficiency depends on the Stokes efficiency which here is 43.2%, the outcoupling efficiency which here is 99%, and the pump quantum efficiency. The pump quantum efficiency of a 2-µm Tm3+ laser pumped around 800 nm hinges on the efficiency of its cross-relaxation process. By fitting the macroscopic cross-relaxation parameter which linearly depends on the Tm3+ concentration to concentration-dependent luminescence-decay data, calculating the overall decay rate of the pump level, and deriving the concentration-dependent pump quantum efficiency, we obtain a theoretical limit for the slope efficiency of 83% for the chosen Tm3+ concentration. The experimental slope efficiency of ~80% closely approaches this limit.

Laser operation of Ti:sapphire rib waveguides fabricated using photolithography and ion beam etching in pulsed laser deposited layers is reported. Polarized laser emission was observed at 792.5 nm with an absorbed pump power threshold of 265 mW, which is more than a factor of 2 lower in comparison to their planar counterparts. Measured beam propagation factors $M^{2}_{x}$ and $M^{2}_{y}$ of 1.3 and 1.2, respectively, indicated single-transverse-mode emission. A quasi-cw output power of 27 mW for an absorbed pump power of 1W and a slope efficiency of 5.3% were obtained using an output coupler of 4.6% transmission with a pump duty cycle of 8%.

Pulsed laser deposition of epitaxial, single-crystal Nd:Gd3Ga5O12 (Nd:GGG) films on Y3Al5O12 substrates with thicknesses up to 135 μm and propagation losses as low as 0.1 dB/cm is reported. Rutherford backscattering spectrometry has shown constant stoichiometry for the films throughout their depth. Fluorescence properties were similar to that of the bulk Nd:GGG crystal used as a target material for the deposition and lasing action has been observed at 1059.0 and 1060.6 nm after pumping by a Ti:sapphire laser operating at 808 nm. A laser threshold of 18 mW has been obtained and a slope efficiency of 17.5% has been observed using an output coupler of 4.5%. The low losses in combination with the high numerical aperture (0.75) and the thickness of the structures make them suitable for high-power diode pumping.

Thick film growth of high optical quality Nd:Gd3Ga5O12 (Nd:GGG) on Y3Al5O12 (YAG) is reported, using the pulsed laser deposition (PLD) technique. Nd:GGG films with thickness up to 135 µm have been grown via sequential deposition runs and up to 40 µm in a single deposition. X-ray diffraction analysis shows that epitaxial growth has occurred and also confirms that the thick Nd:GGG films are single crystal. Analysis by Rutherford backscattering spectrometry shows that the stoichiometry of the thick Nd:GGG films is close to that of bulk Nd:GGG. The thick Nd:GGG films have fluorescence and absorption properties similar to that of bulk Nd:GGG, but slightly broadened. The Findlay–Clay technique of loss calculation has yielded a value of 0.1 dB cm-1 as an estimate of the propagation loss of one of the thick Nd:GGG films that we have subsequently used as a laser medium.

Waveguiding films of Nd:Gd3Ga5O12 with a thickness up to 40 m have been fabricated by pulsed-laser deposition on Y3Al5O12 (1 0 0) substrates. A laser threshold of 18 mW of absorbed pump power has been obtained and lasing action has been observed at 1060.6 nm for pump powers close to the lasing threshold, and at both 1059.0 and 1060.6 nm at pump power levels of approximately 1.5 times above threshold. Waveguide propagation losses of 0.1 dB/cm have been obtained by measuring the absorbed pump power threshold for laser operation at 1060.6 nm for a range of output couplers with various reflectivities. Slope efficiencies of 12.3% and 17.5% were derived using output couplers with a transmission of 2.2% and 4.5%, respectively. The combination of low propagation losses and high numerical aperture for the waveguides indicates the potential of the fabrication technique to produce high quality thick multi-layer waveguides. Such designs are suitable for the development of high-power diode-pumped laser sources of near-diffraction-limited beam quality.

Rib waveguides have been fabricated in pulsed-laser-deposited Ti:sapphire layers using photolithographic patterning and subsequent Ar/sup +/-beam milling. Fluorescence output powers up to 300 /spl mu/W have been observed from the ribs following excitation by a 3-W multiline argon laser. Mode intensity profiles show high optical confinement and the measured beam propagation factors M/sub x//sup 2/ and M/sub y//sup 2/ of 1.12 and 1.16, respectively, indicate single transverse-mode fluorescence emission. Loss measurements using the self-pumped phase conjugation technique have yielded comparable values (1.7 dB/cm) for the ribs and the unstructured planar waveguide counterparts. The combination of optimum modal properties and strong optical confinement, together with sufficient levels of fluorescence output, make the single-moded Ti:sapphire rib waveguides a very interesting candidate as a fluorescence source for optical coherence tomography applications.

Laser experiments were performed on buried, ridge-type channel waveguides in an 8 at. % thulium-doped, yttrium-gadolinium-lutetium codoped monoclinic double tungstate. A maximum slope efficiency of 70% and output powers up to 300 mW about 2.0 μm were obtained in a mirrorless laser resonator, by pumping with a Ti:sapphire laser near 800 nm. To the best of our knowledge, this result represents the most efficient 2 μm channel waveguide laser to date. Lasing is obtained at various wavelengths between 1810 nm and 2037 nm.

Thin films of Er:YAG and Er:YAP were deposited by subpicosecond (450 fs) and nanosecond (20 ns) KrF laser (λ=248 nm) on YAG, YAP, fused silica, silicon and sapphire substrates. Laser spot size, energy density, substrate temperature and deposition ambient (vacuum and oxygen) were varied. Comparison of growth rate, morphology, composition, crystallinity and adhesion of the films grown by subpicosecond and nanosecond deposition is presented.

Thin films of hydroxyapatite were created by laser deposition on real tooth prostheses. Overview of physical and biomedical tests, including unloaded and loaded osseiontegration of experimental minipigs is presented.

Laser experiments were performed on buried, ridge-type channel waveguides in 8 at.% thulium-doped, yttrium– gadolinium–lutetium co-doped potassium double tungstate. By pumping with a Ti:sapphire laser at 794 nm, 1.6 W of output power at 1.84 μm with a maximum slope efficiency of ∼80% was obtained in a laser resonator with a high output-coupling degree of 89%. To the best of our knowledge, this result represents the most efficient 2-μm channel waveguide laser to date.

A detailed study of the fabrication and continuous-wave laser operation of Ti:sapphire channel waveguides written with femtosecond (fs) and picosecond (ps) laser pulses in the bulk of a Ti:sapphire crystal is presented. The waveguides were produced using the double-line approach and the effect of parameters such as the laser pulse duration, repetition rate and interline spacing were investigated for optimizing the laser operation. Structures fabricated by fs-laser pulses (180 fs) exhibited superior performance delivering output powers up 143 mW with a slope efficiency of 23.5% and producing laser emission above a threshold of 84 mW. The emission wavelength was tuned over a wavelength range spanning from 700 to 920 nm using cavity optics with broadband transmission at the lasing wavelength in combination with a birefringent filter in an external cavity.

Lead germanate thin films have been grown on BK7 and silica substrates, using pulsed excimer laser deposition (PLD) at wavelengths of 193 and 248 nm, from a bulk lead germanate target under various partial pressures of oxygen. The films produced vary in colour from brown, through clear, to yellow, and a parametric study has been undertaken of the film properties as a function of the growth conditions. The measured losses of the lead germanate films grown on glass substrates varied from ~ 2.5 to 7 dB /cm depending on the oxygen partial pressure used.

Highly efficient laser action is demonstrated in epitaxially grown Nd:GGG and Ti:sapphire layers. Waveguide losses as low as 0.5 dB/cm are achieved in films of low particulate content, high homogeneity and improved surface morphology obtained by optimized pulsed laser deposition (PLD) configurations. Low threshold laser emission is observed at 800 nm for Ti:sapphire, and at 1060 nm and 937 nm for Nd:GGG waveguides, with slope efficiencies of 26% and 20% respectively. These results verify the versatility of PLD schemes in the fabrication of novel optoelectronic structures.

O3) thin films on glass substrates is performed by pulsed laser ablation of a metallic indium target in an oxygen atmosphere. X-ray diffraction analysis verifies that a transition, from amorphous to polycrystalline film growth, occurs at a temperature of 150 °C. Films grown under optimized conditions exhibit optical transmission higher than 80% in the visible light. Ultraviolet radiation (λ= 325 nm) induced dynamic holographic recording in films deposited at specific temperature and oxygen pressure settings is also demonstrated.

Nd:Gd3Ga5O12 planar waveguides, with significantly improved optical properties over those previously reported, have been fabricated on Y3Al5O12 substrates by pulsed laser deposition. Waveguide losses as low as 0.5 dB/cm have been obtained, determined by measuring the absorbed power lasing threshold with different output coupler reflectivities for both the 1060 nm and 937 nm lasing wavelengths. This order of magnitude improvement in waveguide loss is attributed to the much improved surface morphology and lower particulate count of the thin film samples.

This paper documents the growth of single crystal Ti:sapphire thin films, typically 10µm thick, on undoped sapphire substrates using Pulsed Laser Deposition from a Ti:sapphire single crystal target with a doping level of 0.1 % wt Ti2O3. These thin films are shown to have very high crystal quality using Ion Beam Channelling and X-Ray Diffraction Techniques. The degree of titanium incorporation into the films is investigated using Inductively Coupled Plasma Mass Spectrometry and Particle Induced X-ray Emission. These techniques show that levels of up to 0.08% wt Ti2O3 are present in the deposited layers.

Dielectric channel waveguide lasers are of great interest because of their low pump thresholds and, even more so, high slope efficiencies resulting from the excellent overlap between pump and laser modes and the small transverse channel cross-sections which reduce the volume of active medium that needs to be pumped. Slope efficiencies up to 75% in a femtosecond-written YAG:Yb3+ channel waveguide with an output power of 800 mW [1], 76% in a LiYF4:Tm3+ planar waveguide with an output power of 560 mW [2], as well as 70% and 76% in Tm3+ - and Yb3+ -doped potassium double tungstate channel waveguides with output powers of 300 mW [3] and 650 mW [4], respectively, are state of the art.

Whispering-gallery-mode resonators have been extensively used in conjunction with different materials for the development of a variety of photonic devices. Among the latter, hybrid structures, consisting of dielectric microspheres and colloidal core/shell semiconductor nanocrystals as gain media, have attracted interest for the development of microlasers and studies of cavity quantum electrodynamic effects. Here we demonstrate single-exciton, single-mode, spectrally tuned lasing from ensembles of optical antenna-designed, colloidal core/shell CdSe/CdS quantum rods deposited on silica microspheres. We obtain single-exciton emission by capitalizing on the band structure of the specific core/shell architecture that strongly localizes holes in the core, and the two-dimensional quantum confinement of electrons across the elongated shell. This creates a type-II conduction band alignment driven by coulombic repulsion that eliminates non-radiative multi-exciton Auger recombination processes, thereby inducing a large exciton–bi-exciton energy shift. Their ultra-low thresholds and single-mode, single-exciton emission make these hybrid lasers appealing for various applications, including quantum information processing., Semiconductor nanocrystals are of interest for microlasers that, for example, can be used for integrated photonics applications. Here, Grivas et al. demonstrate single-mode lasing in the single-exciton regime from core/shell CdSe/CdS quantum rods deposited on a single silica microsphere.

Laser experiments on thulium-gadolinium-lutetium-yttrium co-doped monoclinic potassium double tungstates in buried, ridge-type channel-waveguide geometry demonstrate maximum slope efficiencies approaching twice the Stokes limit at ~1.9 μm, when pumping with a Ti:Sapphire laser at 800 nm.

Solid-state organic amplifiers and lasers are attractive for hybrid integration due to their compatibility with different material platforms, straightforward processing, and possibility to optimize easily their optical and electronic properties by molecular engineering. Advances in the gain medium design and synthesis in combination with new resonator architectures led to tremendous improvements in temporal and spectral properties, lifetime stability, gains produced and operating threshold powers, which triggered interest in their use for a broad range of integrated photonic applications. In this contribution, the current state-of-the-art in the field of organic solid-state amplifiers and lasers is reviewed from the aspects of fabrication technology, gain materials, and device performance. Furthermore, examples of the progress of this technology from a laboratory curiosity to one that demonstrates practical integrated photonic applications are highlighted. An outlook is also provided on research areas and applications that are likely to shape further developments of this technology.

Femtosecond-laser-written Ti:sapphire channel waveguides lase at ∼798.25 nm above a threshold pump power of 84 mW with output power and slope efficiency of 143 mW and 23.5%, respectively. Lasing was also observed in picosecond-laser-written channels.

Single-mode lasing at ∼628 nm above an absorbed pump power threshold of 67.5 μW, tunable within a 2.1-nm range (30% of the free-spectral-range) was obtained from colloidal CdSe/CdS core/shell nanorods on whispering-gallery-mode silica microspheres.

Laser experiments on thulium-gadolinium-lutetium-yttrium-co-doped, buried, ridge-type channel waveguides in a monoclinic potassium double tungstate demonstrate a maximum slope efficiency of 69.7% and output powers up to ~300 mW at ~1.9 µm.

Laser experiments on 1.5at.%, 5at.%, and 8at.% thulium-gadolinium-lutetium-yttrium co-doped, buried, ridge-type channel waveguides in a monoclinic potassium double tungstate demonstrate a maximum slope efficiency of 70% and output powers of 300 mW at ∼1.9 μm.

We report, to our knowledge, the first active channel waveguide in Ti:sapphire. We have created [similar to] 1.4-μm high ribs in a [similar to] 10-μm thick Ti:sapphire planar waveguide by reactive ion etching. Following excitation by an Ar-ion laser, the rib structure showed channel-waveguide fluorescence emission. The mode profiles and the beam-parameter values (M2) were measured. The coupling efficiency of fluorescence emission into a single-mode fiber was an order of magnitude higher than for fluorescence from unstructured planar regions of the waveguide. Such devices are of interest as low-threshold tunable lasers and as broadband light sources in low-coherence interferometry.

The tremendous interest in the field of waveguide lasers in the past two decades is largely attributed to the geometry of the gain medium, which provides the possibility to store optical energy on a very small dimension in the form of an optical mode. This allows for realization of sources with enhanced optical gain, low lasing threshold, and small footprint and opens up exciting possibilities in the area of integrated optics by facilitating their on-chip integration with different functionalities and highly compact photonic circuits. Moreover, this geometrical concept is compatible with high-power diode pumping schemes as it provides exceptional thermal management, minimizing the impact of thermal loading on laser performance. The proliferation of techniques for fabrication and processing capable of producing high optical quality waveguides has greatly contributed to the growth of waveguide lasers from a topic of fundamental research to an area that encompasses a variety of practical applications. In this first part of the review on optically pumped waveguide lasers the properties that distinguish these sources from other classes of lasers will be discussed. Furthermore, the current state-of-the art in terms of fabrication tools used for producing waveguide lasers is reviewed from the aspects of the processes and the materials involved.

Sapphire (α-Al(2)O(3)), amorphous and polycrystalline Al(2)O(3), tantalum pentoxide Ta(2)O(5) and the sesquioxides Y(2)O(3), Sc(2)O(3), and Lu(2)O(3) are excellent laser hosts due to their very good thermomechanical properties, broad transparency range and ease of doping with active ions. This article reviews recent research towards the realization of active optical films and the demonstration of gain and laser operation in the waveguides produced from these materials. Compound structures in which laser operation has been demonstrated are highlighted together with the applied fabrication techniques, and details of the laser performance are presented.

Laser operation was achieved in microstructured channel waveguides of KY(WO4)2:Gd3+, Lu3+, Yb3+, resulting in a threshold of only 5 mW, a slope efficiency of 62% versus launched pump power, and 76 mW output power.

A polymer host material, based on a cycloaliphatic diepoxy cured with a fluorinated dianhydride, has been developed. When activated with the rare-earth-ion-doped complex, neodymium(thenoyltrifluoroacetone)3 1,10-phenanthroline, the typical absorption and emission lines of the Nd3+ ion are detected. Luminescence quenching, which usually occurs in polymers due to high-energy vibrations from O–H and C–H chemical bonds, is eliminated by the neutral 1,10-phenanthroline ligand and by applying fluorinated chelates to the complex, respectively, and absorption due to the polymer host occurs only in the wavelength range longer than 1100 nm. Optimization of the fabrication procedure of both, host material and optical structure, leads to steady-state laser emission from a channel waveguide near 1060 nm, providing up to 440 μW of output power from the waveguide structures developed. To the best of our knowledge, this result represents the first steady-state laser in a solid polymer host.

Epitaxially grown, 2.4-microm-thin layers of KY(WO(4))(2):Gd(3+), Lu(3+), Yb(3+), which exhibit a high refractive index contrast with respect to the undoped KY(WO(4))(2) substrate, have been microstructured by Ar beam milling, providing 1.4-microm-deep ridge channel waveguides of 2 to 7 microm width, and overgrown by an undoped KY(WO(4))(2) layer. Channel waveguide laser operation was achieved with a launched pump power threshold of only 5 mW, a slope efficiency of 62% versus launched pump power, and 76 mW output power.

Co-doping with optically inert Gd3+ and Lu3+ ions improves refractive-index contrast and light confinement in KY(WO4)2: Yb3+ planar waveguides. Lasing with 18 mW threshold and record-high slope efficiency of 82.3% versus absorbed pump power is demonstrated.

Air/silica Microstructured Optical Fibers (MOFs) offer new prospects for fiber based sensor devices. In this paper, two topics of particular significance for gas sensing using air guiding Photonic Bandgap Fibers (PBGFs) are discussed. First, we address the issue of controlling the modal properties of PBGFs and demonstrate a single mode, polarization maintaining air guiding PBGF. Secondly, we present recent improvements of a femtosecond laser machining technique for fabricating fluidic channels in PBGFs, which allowed us to achieve cells with multiple side access channels and low additional loss.

Micro-channels were fabricated in hollow-core photonic bandgap fiber (HC-PBGF) and suspended-core holey fiber (SC-HF) by femtosecond Ti:sapphire laser irradiation. Gaseous access was demonstrated via these engineered ports to the core of HC-PBGF and the hollow cladding of SC-HF. Femtosecond laser micro-machining caused no additional transmission loss in HC-PBGFs. This allowed a novel gas cell to be produced, in which gaseous access was provided solely through two micro-channels. Acetylene diffusion was also confirmed through a micro-channel leading to a single cladding airhole in SC-HF. This further highlighted the fabrication technique's precision, selectivity, and potential for developing fiber-based micro-fluidic devices.

Pulsed laser deposition (PLD) has now reached a stage of maturity where the growth of thin films is routine. All that is required is a pulsed ultra-violet (UV) wavelength laser, a vacuum chamber, a target, and a substrate placed in near proximity to the plasma plume. Whether the film that you grow is the film that you need, and whether the thickness, uniformity, optical quality, stoichiometry, degree of crystallinity, orientation and much more is what is desired is another question entirely. PLD is both a science and an art and there are many tricks-of-the-trade that need to be considered to ensure that materials grown are the materials wanted. This paper discusses the practicalities of PLD systems, target geometries, heating regimes for successful epitaxial growth of crystalline films, the problem of particulates, laser sources to use, and in the context of our most recent PLD system, the number of independent lasers and targets used. We show that the use of multiple targets permits a combinatorial approach, whereby stoichiometry can be adjusted to grow designer materials, and in particular multilayer systems, ideally suited for active optical waveguides, a truly demanding end application where optical quality and in-plane losses must be reduced to an absolute minimum.

We present results obtained from the first all-fiber, lensless, optical correlation spectroscopy gas sensor for acetylene (C). In the reported sensing configuration, hollow-core photonic bandgap fiber (PBGF) is employed to contain all gas samples required for optical absorption measurements. This sensor relies upon comparison of the absorption spectrum of acetylene held in a 'reference gas cell' to that of a gas sample under test, which is contained in the 'measurement gas cell'. Ingress of the test gas mixture into the measurement cell is achieved via femtosecond laser-machined microchannels running from the surface of the PBGF to its hollow core. Stable, lensless optical interrogation of the measurement cell is guaranteed by means of arc fusion splices to standard (solid-core) single-mode fiber (SMF). The reference cell is filled with acetylene at atmospheric pressure, and is permanently sealed at both ends by splices to SMF. Therefore, being constructed entirely from optical fiber, both the reference and measurement gas cells are inherently compact and coilable, and dispense with the need for lenses or other free-space optics for connection to the correlation spectroscopy system. We quantify the acetylene concentration of various test gas mixtures and compare our sensor's measured results with computer simulations.

The Laser-Induced Forward Transfer (LIFT) method exists as a relatively simple and versatile additive surface micropatterning technology. Material is transferred from a supported thin film to a receiver substrate by irradiating the rear side of the film with a single laser pulse. Typically transfer is effected either through melting through of the source film or by ablation of the film at a constrained interface with a resultant pressure build-up propelling a piece of the film to the receiver. Both of these processes have inherent advantages and disadvantages; by melting the source film during transfer, sub-laser spot size features can be produced, but the choice of available materials is reduced and control of deposit morphology is limited. Ablation-driven transfer is less material selective but resultant deposits are typically broken during transfer and scattered over relatively large areas.

Description Edited by major contributors to the field, this text summarizes current or newly emerging pulsed laser deposition application areas. It spans the field of optical devices, electronic materials, sensors and actuators, biomaterials, and organic polymers. Every scientist, technologist and development engineer who has a need to grow and pattern, to apply and use thin film materials will regard this book as a must-have resource.

Fabrication and laser operation of proton-implanted Ti:sapphire buried channel waveguides is reported for the first time to our knowledge. Without any postimplantation annealing of the structures, continuous laser operation near 780 nm was demonstrated at room temperature at an absorbed pump power threshold of 230 mW. Single-transverse-mode- laser emission was observed with measured beam propagation factors $M^{2}_{x}$ and $M^{2}_{y}$ of 1.5 and 1.2, respectively. An output power of 12.4 mW for 1 W pump power was obtained with an output coupler of 4.6% transmission at the signal wavelength. Higher output powers were measured in waveguides with larger cross sections exhibiting multimode laser emission.

The authors present the deposition of nanoscale droplets of Cr using femtosecond Ti:sapphire laser-induced forward transfer. Deposits around 300nm in diameter, significantly smaller than any previously reported, are obtained from a 30nm thick source film. Deposit size, morphology, and adhesion to a receiver substrate as functions of applied laser fluence are investigated. The authors show that deposits can be obtained from previously irradiated areas of the source material film with negligible loss of deposition quality, allowing subspot size period microarrays to be produced without the need to move the source film.

Laser emission near 780 nm with 2 mW output power and 3.3% slope efficiency from a Ti:sapphire buried channel waveguide is demonstrated. The sample was fabricated by proton implantation.

We report the fabrication of a low propagation loss (