We report on the possibility to use lasers as a demining tool to dispose mines from a safe distance. Most anti personnel (AP) mines consist of 10 g to 500 g of an explosive, a fuse and a plastic case which makes them very difficult to detect. In 90% of all AP mines trinitrotoluene (TNT) or a combination of TNT and other explosives is used. The interaction of laser radiation with TNT and possible mine wrapping materials is investigated based on spectroscopy and practical considerations. With a CW Nd:YAG laser the desired burning of the explosive is achieved. The interaction is rather based on the absorption of the mine case than on the weak absorption of the explosive. A portable CW Nd:YAG laser is described and experiments with real AP mines are performed. We have investigated the behavior of four different representative blast AP mines under laser irradiation at Bofors test centre in Sweden. Disposal of all available mines from a safe distance up to 50 meters is achieved. Laser incident power was in the range from 20 W to 60 W. Due to partial burning of the explosive charge the resulting detonation of mines is considerably reduced.

The multimode and depolarized output beam of a highly multimode diode-pumped Yb-doped fiber amplifier is converted to a diffraction limited, linearly polarized beam by a self-referencing two wave mixing process in an infrared sensitive photorefractive crystal (Rh:BaTiO₃). Up to 11.6W singlemode output is achieved with a 78% multimode to singlemode photorefractive conversion efficiency.

Light sources with a broad spectral output and diffraction limited beam quality have a wide variety of present and future applications. A few of particular interest are hyperspectral laser radar for environmental monitoring, active hyperspectral imaging for detection and identification of objects, and speckle-free illumination. With the exception of systems based on amplified femto- or picosecond lasers, which are large and extremely complicated, pulse energies from supercontinuum laser sources have been limited to <10 microJoules which is generally not sufficient for the applications listed above. We present a simple technique to generate broadband light spanning several hundred nanometers in the near infrared with pulse energies of ~1 mJ, an improvement of approximately two orders of magnitude. The system is comprised of a Q-switched Nd:YAG laser and a very large mode area photonic crystal fiber. A combination of cascaded stimulated Raman scattering, four wave mixing, and self-phase modulation is responsible for the spectral broadening. Possibilities of scaling the output to the ~10 mJ level as well as extending the spectral coverage to the visible and mid-infrared will also be discussed.

We report power-scaling of an ytterbium-sensitized thulium-doped silica fiber laser generating up to 75 W of output power in the 2 μm wavelength range when cladding-pumped by a 975 nm diode stack. The slope efficiency is 32% with respect to launched pump power and the beam quality factor (M²) is 1.3. We also investigate the characteristics of this fiber in a tunable laser configuration, operating at ~10 W of output power with the tuning range extended from 2000 to 2080 nm at a launched pump power of 40 W.

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.

We report on efficient operation of Ho:YAG and Ho:YLF lasers in-band pumped by a tunable Tm-doped silica fiber laser. The Tm-doped fiber laser could be tuned over 150 nm from ~ 1860 to 2010 nm with a relatively narrow linewidth (<0.5 nm) at output power levels in excess of 9 W with a high power stability (RMS < 1.5%). Using a simple standing-wave cavity configuration, >6.4 W of TEM_oo output was obtained from a Ho:YAG laser at 2.1 μm at the maximum incident pump power of 9.6 W at 1907nm from the Tm fiber laser, corresponding to an optical-to-optical efficiency of 67%, and the slope efficiency with respect to incident pump power was 80%. For a similar resonator design, 4.8 W of output at 2.07 μm was generated from a Ho:YLF laser at an incident pump power of 9.4 W, corresponding to an optical conversion efficiency of 51%. The different levels of performance of the Ho:YAG and Ho:YLF are compared and their relative merits discussed. Using a simple ring resonator geometry and an acousto-optic modulator to enforce unidirectional operation, we have obtained 3.7 W of single-longitudinal-mode output from a Ho:YAG laser. The prospects for further improvement in performance and higher output power are discussed.

We present a simple design for efficient generation of high average power in the 3-5 μm wavelength range. Using a 15 W thulium-doped fibre laser to pump a Q-switched 2.1 μm Ho:YAG laser, we obtain 9.2 W average output power with excellent beam quality. The 2.1 μm output is used to pump a ZnGeP₂-based OPO, resulting in 4.6 W average output power in the 3.6-5.2 μm range with beam quality M² < 1.4.

We demonstrate an optical parametric oscillator (OPO) based on GaAs. The OPO utilized an all-epitaxially-grown orientation-patterned GaAs (OP-GaAs) crystal, 0.5-mm-thick, 5-mm-wide, and 11-mm-long, with a domain reversal period of 61.2 μm. By tuning either the near-IR pump wavelength between 1.75 and 2 μm, or the temperature of the GaAs crystal, the mid-IR output tuned between 2 and 11 μm, limited only by the spectral range of the OPO mirrors. The pump threshold of the singly-resonant OPO was 16 μJ for the 6-ns pump pulses, and the photon conversion slope efficiency reached 54%. Also, we show experimentally the possibility of pump-polarization-independent frequency conversion in GaAs.

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.

A summary of results of a femtosecond optical parametric oscillator driven by a diode-pumped, all-fibre mode-locked laser system is given. In addition, a number of parametric oscillator devices with enhanced capabilities including extended tuning ranges throughout the infrared with greater spectral control and frequency tuning agility are described.

Zinc germanium phosphide (ZGP) is well suited to use in optical parametric oscillators (OPOs) for conversion of near-infrared laser output into the mid-infrared waveband (3 to 5 μm). Typical OPO applications seek to exploit pump wavelengths close to 2 μm so that both the output wavelengths fall within the mid-infrared waveband. However, the material typically suffers optical loss arising from growth defects that becomes significant at wavelengths below about 2.5 μm. We report the results of calorimetric studies that show that the loss can comprise both absorptive and scattering components. We have assessed the affect of loss at the pump wavelength on the conversion efficiency of a high pulse repetition frequency, doubly-resonant, ZGP OPO pumped with 2.094 μm radiation generated by a wavelength doubled Nd:YLF laser. The OPO used crystals having loss coefficients in the range 0.03 cm^-1 to 0.3 cm^-1. The reduction in slope efficiency for the conversion process was evaluated over a range of pump beam diameters (1/e² intensity) from 0.12 mm to 0.30 mm. For the largest beam diameter a slope efficiency of 57% was measured for a ZGP OPO crystal having a loss coefficient of 0.03 cm^-1. The slope efficiency reduced to about 30% when the loss coefficient was increased to 0.3 cm^-1.

We have studied the generation of terahertz (THz) waves by optical parametric processes based on laser light scattering from the polariton mode of nonlinear crystals. Using parametric oscillation of MgO-doped LiNbO₃ crystal pumped by a nano-second Q-switched Nd:YAG laser, we have realized a widely tunable coherent THz-wave sources with a simple configuration. We have also developed a novel basic technology for THz imaging, which allows detection and identification of chemicals by introducing the component spatial pattern analysis. The spatial distributions of the chemicals were obtained from terahertz multispectral trasillumination images, using absorption spectra previously measured with a widely tunable THz-wave parametric oscillator. Further we have applied this technique to the detection and identification of illicit drugs concealed in envelopes. The samples we used were methamphetamine and MDMA, two of the most widely consumed illegal drugs in Japan, and aspirin as a reference.

Room temperature CW operation of quantum cascade lasers has recently been demonstrated. However, this important performance milestone still remains a technological challenge. QCLs are characterized by high electrical power consumption (3 - 5 W) and low wall plug efficiencies (1 - 4%). This leads to considerable self-heating that can block CW operation. In order to overcome this self-heating device fabrication has to be optimized for high thermal extraction. In this paper we will demonstrate the factors that influence CW operation in quantum cascade lasers (QCLs). We will compare the performance of different device processing design to achieve maximum thermal dissipation and reduced power consumption.

The principle ideas of the thin disk laser design will be illustrated and the advantages for operating different laser materials will be explained. The results for cw- and q-switched operation as well as for amplification of short (ns) and ultra-short (ps, fs) pulses demonstrate the potential of the thin disk laser design. The scaling laws for this laser design show that the power limit for cw-operation is far beyond 10 kW for one single disk and the energy limit is higher than 1 J from one disk in pulsed operation. Also the applicability of the thin disk laser concept to optically pumped semiconductor structures will be discussed. When pumping directly into the quantum wells the energy defect between pump- and laser photon can be smaller than 5% thus reducing the waste heat generated inside the semiconductor structure. First results demonstrate the potential of this new concept. Finally, a short overview of the industrial realization of the thin disk laser technology will be given.

We have developed Al-free tapered laser structures for both high brightness and reliability. The Al-free active region consists of a separate confinement heterostructure (SCH) with a GaInAsP large optical cavity (LOC) to provide low optical losses and a strained GaInAs quantum well for high gain. Broad-area lasers diodes (100 μm width) were fabricated with low internal losses (< 2.3 cm^-1), high internal efficiency (98%) and a low transparency current density (100 A/cm²). In order to control the spatial beam quality along the slow axis, we fabricated low aperture tapered laser structures. On a single tapered laser, we have obtained an output power of 1 W at 1.5 A together with a wall-plug efficiency of 44%. Furthermore, we have fabricated high brightness mini-bars of index guided tapered lasers at 980 nm (emissive area 2.7 mm) emitting a power of 25 W CW at 15°C and 50 W QCW at 25°C with low slow axis angles. Thanks to high power and low far-field width (FWHM=3.5° at 20 W), we demonstrate 11 W of output power coupled into a 100 μm diameter optical fiber from a single mini-bar, by means of a collective beam shaping technique.

Experimental results based on rare-earth-doped fibers have impressively shown that fiber lasers and amplifiers are an attractive and power scalable solid-state laser concept. Based on ytterbium-doped large-mode-area double-clad fibers, in the continuous regime, output powers approaching the kW-range with diffraction limited beam quality have been shown. Average output powers in the order of 100 W have been demonstrated in the pulsed regime even for femtosecond fiber lasers. Further power scaling is limited by the end facets damage, thermo-optical problems or nonlinear effects. To overcome these restrictions microstructured fibers with several new preferable features can be used. In our contribution we will discuss power scaling of fiber lasers and amplifiers in the multi kW-range with excellent beam quality based on rare-earth-doped photonic crystal fibers.

The last two years has seen rapid development in the field of fiber lasers. In particular, reported output powers have dramatically increased by several orders of magnitude, from 10W to 1KW. While the generic benefits of fiber lasers are well known (e.g. efficiency and compactness), the power scaling of these devices does present challenges that need to be addressed before the deployment of reliable systems is achieved. In this contribution, we address optical branching component requirements for High Power Fiber Lasers (HPFLs). Monolithic, fused fiber devices are clearly the component of choice to enable fully integrated, reliable HPFLs. The required components can be classed in two distinct groups. The first group are single mode devices whose function relies on cladding coupling based on fused biconical tapers and these include tap couplers, wavelength combiners/splitters, and filters. The second group includes multi-mode devices, primarily used for the power combining of multi-mode pump diodes. We describe the latest developments in state-of-the-art fused fiber components for HPFL systems, including the use of low ratio tap couplers for optical feedback and control in fully integrated fiber laser systems of up to 100W.

Coherent solid-state optical sources based on Nd:YAG/Cr⁴⁺:YAG passively Q-switched microchip lasers cover the spectral range from 5000 to 200 nm, producing multikilohertz pulse trains with pulse durations as short as 100 ps and peak powers up to 1 MW. The wavelength diversity is achieved through harmonic conversion, parametric conversion, Raman conversion, and microchip-laser-pumped miniature gain-switched lasers. In all cases, the optical heads have been packaged in a volume of less than 0.5 liters. These compact, robust devices have the proven capability to take what were complicated laser-based experiments out of the laboratory and into the field, enabling applications in diverse areas. The short pulses are useful for high precision ranging using time-of-flight techniques, with applications in 3-dimensional imaging, target identification, and robotics. The short pulse durations and ideal mode properties are also useful for material characterization. The high peak powers can be focused to photoablate material, with applications in laser-induced breakdown spectroscopy and micromachining. Ultraviolet systems have been used to perform fluorescence spectroscopy for applications including environmental monitoring and the detection of biological aerosols. Systems based on passively Q-switched microchip lasers, like the lasers themselves, are small, robust, and potentially low cost, making them ideally suited for field applications.

The anomalous linewidth behavior in a DFB fiber laser is investigated. It is shown that not only does the linewidth deviate drastically from the Schawlow-Townes linewidth formula by increasing with pump and laser power, but it also varies significantly with the pumping configuration used. These results have potentially important implications for the design and operation of such fiber lasers.

Laser remote sensing has become a versatile and widely applied tool for the detection and characterization of a variety of hard and soft targets. For applications where eye safety is an issue these sources are usually in the infrared. Mission needs often dictate transmitter parameters that require unusual laser wavelengths and waveforms that are not commercially available. Waveform requirements can include ns-class pulses for precision ranging; single-frequency 100s-ns pulses for velocity measurements; frequency-agile sources for chemical sensing; high-energy, J-class, pulses for long-range environmental sensing; and adaptive waveforms for in-situ transmitter optimization or multi-function sensors. Additionally, in the case of airborne and space-based sensors, platforms often dictate stringent size, weight and power constraints. This paper discusses laser transmitter requirements for a variety of laser remote sensing missions and describes novel pulsed solid-state sources under development at CTI to meet these needs. Current work includes the development of high-efficiency Nd:YAG, Er:YAG and Ho:YAG lasers, high power Tm:YALO lasers, high-energy Tm:YAG amplifiers, broadly tunable Cr:ZnSe lasers, short-pulse Raman lasers, and wavelength-agile optical parametric oscillators.

Recent developments in pulsed Doppler lidar technology for range-resolved aerosol and hard-target imaging applications are presented. Systems based upon CO₂ and fiber-optic technologies at wavelengths of 10.6 μm and 1.5 μm respectively are described. Data are presented showing aspects of system and component development as well as recent field deployments.

We present an overview of diode-pumped solid-state lasers with negative feedback stabilization. Active stabilization by means of direct modulation of cavity losses was utilized in several Nd-based quasi-continuous-wave lasers mode-locked by saturable Bragg reflectors (SBR). The stabilization acts to eliminate the relaxation-oscillation-driven spiking after laser oscillation turn-on. Stable continuous-wave modelocking was observed in as little as 10 μs after laser turned on where the leading spike was reduced or completely eliminated dependent on the gain material and the operating wavelength. Stabilization was also used to prevent Q-switching instabilities in a continuous-wave SBR-modelocked Nd:KGW laser resulting in an extended operational parameter range and pulse shortening by up to 35%. Stabilization of passively mode-locked lasers could alternatively be achieved using an intra-cavity element exhibiting nonlinear absorption, which was demonstrated using an Indium Phosphide plate. Pulse shortening by up to 30% was permitted as the modulation depth of the SBR could be increased whilst maintaining stable cw modelocking. Active stabilization was also employed for Tm-based lasers emitting in the 1.9 - 2 μm wavelength region as these lasers suffer from inherent amplitude instability and sensitivity to cavity perturbation. Passive stabilization of a Tm:YAlO laser utilizing a germanium plate was also investigated.

Three aspects of filament formation due to self-focusing are investigated. In the first the generation of a horizontal array of stable white light (super) continuum (WLC) filaments in water has been observed using a cylindrical plano-convex lens. Far field interference patterns are observed suggesting that the optical paths and phase stability between neighbouring filaments is remarkably constant. The pattern created by a filament pair is similar to that due to a pair of Young’s slits. The experimental results agree well with theoretical predictions based on the number of fringes and the fringe spacing. These observations suggest that regular arrays of WLC filaments may be treated as phased arrays to steer the beam in the far field. In the second investigation the effect of beam quality on self-focusing has been studied. The small intrinsic aberration of a high quality TEM₀₀ beam is shown to cause hot-spots leading to multiple filaments. In the third investigation a circular aperture is used to create a Fresnel diffraction pattern. It is shown that self-focusing (a pre-requisite for filament formation) occurs in the presence of the aperture but that no formation is observed when the aperture is removed, even though the beam has higher power well above the threshold for critical power. An analytical solution to the Huygens-Fresnel diffraction integral shows that the axial intensity oscillates between maxima and minima as the distance from the aperture increases and that filament formation coincides with the presence of an axial maximum.

The development of high-speed integrated photonic devices requires accurate modeling tools, especially for high-bandwidth devices and devices operating near the bandgap. Models of femtosecond pulse propagation in a semiconductor are typically developed in the time domain and must include dispersion and loss effects because of the extensive bandwidth. In the past, approximate “classical” models such as the Lorentzian model of the optical properties have been used to study pulse propagation of femtosecond pulses in semiconductors. Quantum-mechanical models such as that developed by Adachi provide accurate spectral characteristics of dispersion and loss as a function of temperature. The present work describes a detailed comparison between the two approaches. In solving realistic problems, numerical methods such as FDTD must be employed. This requires a time domain representation of the susceptibility. For the case of a simple resonator structure, an exact analytic time domain solution was previously obtained using the classical model. This can be used to verify the appropriateness of our numerical solutions when applied to the more complicated Adachi model. The Adachi model more accurately takes into account the absorption features near the band edge, which can profoundly affect the pulse shape in the femtosecond regime. In this comparative study, these effects are examined for simple resonator structures which contain GaAs.

Temporal and spatial changes in the matrix of glasses (BK7 glass, fused silica, quartz) and sapphire are investigated during and after irradiation by pulsed laser radiation (100 fs < t_p < 3 ps) at the wavelength λ = 800 nm using high-speed photography, transient absorption spectroscopy, and Nomarski-microscopy in order to visualize the changes of optical properties, the plasma formation and expansion, the stress formation, the modification, and the cracking as well. Depending on the excitation conditions the glasses and sapphire exhibit different excitation and relaxation channels including various types of defect centers. Compared to laser radiation with pulse durations in the nanosecond regime the glasses and sapphire are heated within the irradiation zone for many nanoseconds resulting in modification by an increase of the refractive index without cracking, enabling the generation of photonic structures within the bulk. Irradiation at pulse durations in the picosecond regime originates in cracking enabling the marking and microstructuring in the bulk and at the surface.

During the last decade it has been proven that focused femtosecond laser pulses are an ideal tool for micro- and sub-micro-structuring of all kinds of materials. Due to the high intensities that can be achieved in ultrashort pulses they can be applied for machining transparent media within the volume by means of multi-photon absorption. Besides ablative methods, multi-photon absorption can also lead to photo-polymerization of light-sensitive resins, i.e. two-photon polymerization. In this paper we present our latest results on the fabrication of 3D microstructures by means of two-photon polymerization.

Multiphoton excitation of selected dye molecules for laser-induced fluorescence diagnosis (LIFD) and optical biopsy of biological tissue and microbiological samples has various advantages: greater tissue penetration, more spatial resolution and less photo-bleaching. New applicators and microscopical set-ups for the delivery of the fs-pulsed laser radiation as required for multiphoton LIFD and optical biopsy need to be developed. Beam delivery solutions and workplaces for microbiological and tissue diagnosis are presented.

We have investigated many different type of solid-state lasers and the materials that can passively Q-switch, mode-lock, Q-switched mode-lock all the above solid-state lasers. In the advanced applications of the solid-state lasers, the microchip laser configurations had been used satisfactory for nearly the past decade. In all the microchip laser developments, the only tolerance that can reduce the physics size, optimize the modulated output efficiency and minimize the component price is to use the doped single crystal semiconductor saturable absorbing modulators as we have published. Here we use the MEMS technologies for the fabrication of the most compact, highest efficiency and most low price semiconductor substrate microchip laser. Two out of four components of the various OPO microchip lasers, that generate visible, near infrared and infrared wavelengths and with Q-switch, mode-lock, Q-switched mode-lock modulation could be achieved.

Optical parametric oscillators (OPOs) using zinc germanium phosphide (ZGP) crystals as the active non-linear medium are important devices for wavelength conversion into the 3 to 5 μm mid-infrared waveband. However, the presence of optical absorption within ZGP at the pump wavelength can lead to detrimental thermo-optic effects (thermal lensing and dephasing) when operated under high average power conditions. In order to characterise the strength of thermal effects within ZGP OPOs a theoretical model is under development based on the commercially available software package GLAD. Pump, signal and idler beams are represented by transverse arrays of complex amplitudes and propagated according to diffraction and kinetics algorithms. The ZGP crystal is modelled as a series of crystal slices, using a split-step technique, with the effects of non-linear conversion, absorption and thermal effects applied to each step in turn. We report modelling predictions obtained to date for the strength of the thermal lens induced in a ZGP crystal on exposure to a 5 Watt Q-switch pulsed high-repetition rate (10 kHz) wavelength doubled Nd:YLF laser at 2.094 μm. Predicted steady-state thermal focal lengths and time constants are compared to experimental results measured for two ZGP crystals, with high and low pump absorption levels. GLAD model predictions for a singly-resonant ZGP OPO in the absence of thermal effects are also compared to predictions from the widely available software package SNLO.

One route to generating mid-infrared (mid-IR) radiation is through a two-stage non-linear conversion process from the near-IR, exploiting powerful neodymium lasers operating at wavelengths close to 1 μm. In the first stage of this process non-linear conversion within a degenerate optical parametric oscillator (OPO) is used to double the wavelength of the 1 μm laser. The resultant 2 μm radiation is then used to pump a second OPO, based on a material such as ZGP, for conversion into the 3 to 5 μm mid-IR waveband. Periodically poled lithium niobate (PPLN) is a useful material for conversion from 1 to 2 μm due to its high non-linear coefficient (d_eff ~ 16 pm/V) and the long crystal lengths available (up to 50 mm). Slope efficiencies in excess of 40% have readily been achieved using a simple plane-plane resonator when pumped at 10 kHz with 3.5 mJ pulses from a 1.047 μm Nd:YLF laser. However, the OPO output was spectrally broad at degeneracy with a measured full-width-half-maximum (FWHM) linewidth of approximately 65 nm. This output linewidth is significantly broader than the spectral acceptance bandwidth of ZGP for conversion into the mid-IR. In this paper techniques for spectral narrowing the output from a degenerate PPLN OPO are investigated using two passive elements, a diffraction grating and an air spaced etalon. Slope efficiencies approaching 20% have been obtained using the grating in a dog-leg cavity configuration producing spectrally narrow 2 μm output with linewidths as low as 2 nm. A grating-narrowed degenerate PPLN OPO has been successfully used to pump a ZGP OPO.

We report a narrow-linewidth (Δλ = 0.4 nm) optical pulsed MOPA (master oscillator - power amplifier) source emitting 0.41 mJ pulses (1.5 kW peak power) in the eye-safe range (λ = 1548 nm). Pulse duration and repetition rate were 90 ns and 5 kHz respectively.

In this paper we report the spectroscopic data for samples of 0.031% iron, 0.017% nickel, 0.01% chromium and 0.017% cobalt (molar) doped gallium lanthanum sulphide (GLS) glass. Photoluminescence (PL) with a full width half maximum (FWHM) of around 500 nm and peaking between 1120 nm and 1460 nm is observed when excited using wavelengths of 850 nm and 1064 nm. The emission lifetime for nickel-doped GLS at 300 K was measured to be 40 μs. Photoluminescence excitation (PLE) peaks for chromium-doped GLS at 700 nm and 1020 nm have been observed. By comparisons of our spectroscopic data to that of transition metals doped into other hosts we determine the oxidation states of the transition metal ions and propose transitions for the observed spectroscopic peaks.

In this paper we describe an Er:YAG laser pumped by a tunable, cladding-pumped Er,Yb fiber laser and discuss factors affecting the laser performance. Crystals with different Er³⁺-concentrations in the range 0.5% to 4 at% and with crystal lengths selected for ~95% absorption of the pump light at 1532nm were used, and the laser performance was investigated for a range of output coupler transmissions (2-30%) at 1646nm. In preliminary experiments we have achieved a maximum output power of 4W at 1646nm for 11W of absorbed pump power corresponding to an efficiency of 36%, using a crystal with 0.5at% Er³⁺-concentration and an output coupler transmission of 10%. Our experiments have revealed that the cw efficiency decreases quite markedly for higher Er³⁺-concentrations. The origin this behavior is currently the subject of a detailed experimental investigation and our preliminary findings will be presented. The prospects for further increase in output power and efficiency will also be discussed.

We have developed Fabry-Perot lasers at λ=852nm, using an Aluminium free active region with the aim to develop a single-frequency and single-mode device for atomic clocks for the future European positioning system Galileo. The device is a separate confinement heterostructure with a GaInP large optical cavity and a 8nm compressive-strained GaInAsP quantum well. The broad-area laser diodes are characterised by low internal losses (<3 cm^-1), a high internal efficiency (94%) and a low transparency current density (100A/cm²). We obtain a low threshold current density (245A/cm²) and a high slope efficiency (0.9 W/A) for 2mm long broad area (100μm wide) AR/HR coated devices. We measure an optical power of more than 5.5W (I= 8.5A), under CW operation at 15°C, with a maximum wall-plug efficiency of 0.45. The laser emission is achieved up to at least 115°C. An optical power of more than 1.4W is obtained at 100°C (I=3.6A). At 852nm, we obtain an optical power of 1.2W (I=1.7A, 15°C). The low divergences of the fast axis far field - a FWHM of 31.8° and a total angle of 61.8° at 1/e²- are very stable with the current.

High average power sources operating in the 3 to 5 μm mid-infrared waveband are of interest for a wide variety of applications. We present design and performance results for a high-power engineered breadboard mid-IR source based on near-infrared pumped periodically-poled lithium niobate (PPLN) optical parametric oscillator (OPO) technology. The source design utilises a pair of singly-resonant PPLN OPOs pumped by a commercial 40 Watt, Q-switched, diode-pumped Nd:YLF laser. The mid-IR outputs from each OPO are polarisation recombined into a single output beam. A twin OPO design was chosen to minimise the effect of optical absorption, reduce thermal loading within each PPLN crystal and provide additional flexibility by offering the option for dual-wavelength mid-IR operation. An average output power approaching 4 Watts has been obtained with a corresponding slope efficiency of 15%. The mid-infrared beam is 6 times diffraction limited. Laser operation is controlled by a remote PC link and power, spectral and temporal pulse diagnostics are included within the system.