This PDF file contains the front matter associated with SPIE Proceedings Volume 8039, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Monoclinic crystals of Tm-doped KLu(WO₄)₂ were used to demonstrate pulsed laser operation near 2 μm. Passive Qswitching and passive mode-locking were the techniques employed to produce such laser pulses. For passive Qswitching we used an AlGaAs -based diode laser to pump the active elements and Cr:ZnSe and Cr:ZnS crystals as saturable absorbers. For passive mode-locking we used a Ti:sapphire laser as pump source and single-walled carbon nanotubes as saturable absorbers. In the former case, maximum pulse energies of 200 μJ for a pulse duration of 70 ns were achieved at a repetition rate of 3 kHz with Cr:ZnS saturable absorber, while in the latter case, ultrashort pulse durations of ~10 ps were measured with a maximum average power of 240 mW. In both laser regimes the oscillation wavelength was ~1945 nm.

We report results for high quality transparent ceramic window materials (spinel and β-SiC) and high power solid state laser materials (Yb:Y₂O₃ and Yb:Lu₂O₃). Spinel ceramic demonstrates a record low absorption loss of 6 ppm/cm at 1.06 μm. We also report optical transparency from a β-SiC ceramic fabricated by the Spark Plasma Sintering technique. Capability of fabricating various shape and size of spinel ceramics is also demonstrated. We report lasing in hot pressed Yb³⁺:Y₂O₃ and Yb³⁺:Lu₂O₃ ceramic made from co-precipitated powder. Highest output power and efficiency from heavily doped Yb³⁺ doped Lu₂O₃ ceramic are reported.

5 at% Tm-doped NaGd(MoO₄)₂ laser crystal operated in CW conditions provided up to 641 mW of output power at λ ≈ 1910 nm with a slope efficiency of 50.8% and a pump power laser threshold of 166 mW. 10 at% Tm-doped Li₃Ba₂Lu₃(MoO₄)₈ laser operated in quasi-CW conditions provided up to 510 mW of output power at λ ≈ 1950 nm with a slope efficiency of 71.4% and a pump power laser threshold of 125 mW. Both crystals were grown by the Top Seeded Solution Growth method at about two hundreds degrees below their melting points. The structural disorder of these crystals confers inhomogenous broadening to the Tm³⁺ electronic transitions. Slightly broader laser tuning range and laser emission bandwidths are observed in the Li₃Ba₂Lu₃(MoO₄)₈ crystal despite of the lower expected degree of crystalline disorder. The crystals are promising for the development of mode locked ultrafast (fs) lasers with emission close to λ = 2 μm.

We report what is believed to be the first laser operation based on Ho³⁺-doped YVO₄. The Ho⁺³: YVO₄ was resonantly diode-pumped at ~1.93 μm to produce up to 1.6 W of continuous wave (CW) output power at ~2.054 μm. The laser had a slope efficiency of ~38% with respect to absorbed power. We have measured the absorption and stimulated emission cross sections of The Ho⁺³: YVO₄ at 77 K and present the calculated gain cross section spectrum at 77 K for different excited state inversion levels.

Yb:YAG thin-disk laser performance at room and cryogenic (80K) temperatures is presented. The Yb:YAG gain media, which is Indium soldered to specialized CuW mounting caps, is cooled using either a pressurized R134A refrigerant system or by a two-phase liquid nitrogen spray boiler. At cryogenic temperatures spontaneous emission measurements reveal sharper transition lines and a decrease in the fluorescence lifetime. Lasing reflects that a true four-level laser. Interchangeable mounting caps allow the same Yb:YAG media to be switched between the two systems. This allows direct comparison of lasing, amplified spontaneous emission, and temperature performance at 15 °C and at -200 oC.

New generation of eye safe military applications such as range finding, short range illumination and friend or foe identification have started to use the 1550nm wavelength region. This was encouraged by the advent of diode lasers efficient enough to approach the output power of shorter wavelength, 850nm and 905nm devices. This paper will review the actual performance and technologies of various commercially available 1550nm pulsed laser diodes. The performance and reliability of a new high brightness 1550nm semiconductor laser diode are disclosed and compared. Peak power of up to 35 Watts is achieved out of a single junction 350 micron stripe laser. Similarly, peak power in excess of 20W is achieved with a 180 micron stripe laser. This represents an optical power density of 11.1M W/cm². Other key advantages of this new laser are a fast axis FWHM divergence of 25 degrees and less than a 10mRad divergence after fast axis collimation. The new diode technology will be explained in some detail covering aspects of design, fabrication and adaptation to meet its final target performances. A description of the optimization of chip dimensions and laser packaging is also undertaken. Finally, various ideas are offered to further improve the laser efficiency and power.

We present breakthrough performance from green and blue InGaN-based laser diodes fabricated on nonpolar/semipolar substrates. High-power, high-efficiency, and long-lifetime continuous-wave laser operation is demonstrated using these novel crystal orientations. For green wavelengths at 520 nm, we report on continuous wave single mode lasing with75 mW of output power and wall plug efficiencies over 2.3%. In the blue regime we describe single-mode lasers operating with over 23% wall plug efficiency and with output powers greater than 750 mW. These InGaN-based direct-diode lasers offer significant improvement in performance, size, weight, and cost over conventional gas and solid state lasers. Furthermore, these devices exhibit robust operation over a broad temperature range, can be directly modulated and do not contain harmful residual infrared radiation typical of second harmonic generation lasers. These characteristics are salient considerations for such optical devices in battlefield and other security applications.

Advanced solid state laser architectures place increasingly demanding requirements on high-brightness, low-cost QCW laser diode pump sources, with custom apertures both for side and end rod pumping configurations. To meet this need, a new series of scalable QCW pump sources at 808nm and 940nm was developed. The stacks, available in multiple output formats, allow for custom aperture filling by varying both the length and quantity of stacked laser bars. For these products, we developed next-generation laser bars based on improved epitaxial wafer designs delivering power densities of 20W/mm of emission aperture. With >200W of peak QCW power available from a full-length 1cm bar, we have demonstrated power scaling to over 2kW in 10-bar stacks with 55% wall plug efficiency. We also present the design and performance of several stack configurations using full-length and reduced-length (mini) bars that demonstrate the versatility of both the bar and packaging designs. We illustrate how the ROBUST HEAD packaging technology developed at SCD is capable of accommodating variable bar length, pitch and quantity for custom rod pumping geometries. The excellent all-around performance of the stacks is supported by reliability data in line with the previously reported 20 Gshot space-grade qualification of SCD's stacks.

We describe the successful use of wavefront compensator phaseplates to extend the locking range of VHG-stabilized diode laser bars by correcting the effects of imperfect source collimation. We first show that smile values of greater than 1μm peak to valley typically limit the achievable wavelength locking range, and that using wavefront compensation to reduce the effective smile to below 0.5μm allows all emitters to be simultaneously locked, even for bars with standard facet coatings, operating under conditions where the bar's natural lasing wavelength is over 9nm from the VHG locking wavelength. We then show that, even under conditions of low smile, wavefront errors can limit the locking range and locking efficiency, and that these limits can again be overcome by wavefront compensation. This allows wavelength lock to be maintained over an increased range of diode temperature and drive current, without incurring the efficiency loss that would be incurred by increasing grating strength. By integrating wavefront compensation into the slow-axis collimator, we can achieve this high-brightness VHG-optimized beam in a compact optical system.

We have demonstrated an all-fiber thulium laser system that, without any intracavity polarizing elements or freespace components, yielded a stable polarization extinction ratio (PER) of ~18 dB. The system is based on singlemode polarization-maintaining silica fiber and its cavity is formed from each a high and low reflectivity femtosecond laser written fiber Bragg grating resonant at 2054 nm. The output of the fiber is not only highly polarized, but maintains a narrow linewidth of 78 pm at its maximum output power of 5.24 W. The high PER without any polarizing elements in the cavity is of great interest and makes the systems useful for spectral beam combining and other applications which require polarization dependent optical elements.

We present theoretical and experimental results of a 130 W continuous-wave (CW), single-frequency, 7 m, polarizationmaintaining (PM) Yb:doped fiber (25/400) μm amplifier simultaneously seeded with a combination of broadband and narrow-line signals. Experiments were performed for two thermal configurations and the SBS threshold of the doubly seeded amplifier is compared to the singly seeded case. In the first configuration, the fiber was wrapped around a cold spool held at 12° C to diminish thermally induced shifts in the acoustic resonance of the fiber, which is known to suppress stimulated Brillouin scattering (SBS). In this case, over 80 W of single-frequency output was obtained demonstrating an enhancement of 3 dB in the SBS threshold compared to the single-tone case whereby the SBS threshold was 40 W. In the second thermal configuration, 6 m of the fiber is wrapped around the same cold spool, but approximately 1 m of the fiber is left to cool in ambient conditions. In this case, an optically induced thermal gradient was formed due to the quantum defect heating associated with power transfer from the pump and broadband seed signals into the single-frequency signal at the output end of the fiber. Over 130 W of single-frequency output was demonstrated yielding an effective increase of ~5 dB in the SBS threshold when compared to the single-tone case.

We describe the generation and amplification of femtosecond pulses at 2-μm wavelength in thulium doped fiber. The mode-locked oscillator is a ring cavity based on single-mode Tm:fiber producing stable soliton pulses at 70 MHz repetition rate with 40 pJ pulse energy, centered at ~1.97 μm wavelength with ~8 nm (FWHM) spectral width. These pulses seed a Tm:fiber based Raman amplifier, which increases the energy up to 9 nJ. The spectrum is broadened up to 40 nm (FWHM) and the center wavelength can be shifted from ~1.97- 2.15 μm. The Raman solitons are inherently time-bandwidth limited with pulse durations <150 fs.

We present a Tm:fiber based broadband ASE source which was used for atmospheric CO₂ detection. The average spectral power of this source was limited to ~6.1 μW/nm which was the main limitation in detection of trace concentrations of gases. This shortcoming was overcome by using an ultrashort pulsed Raman amplifier system with maximum of ~127 μW/nm of spectral power density which was able to provide sensitivity better than 300 ppm for CO₂. In addition, improving the average power of the ASE provided an essential tool in lab to characterize optical elements with sharp spectral features around 2 μm.

TeraDiode has produced ultra-high brightness fiber-coupled direct diode lasers. A fiber-coupled direct diode laser with a power level of 1,040 W from a 200 μm core diameter, 0.18 numerical aperture (NA) output fiber at a single center wavelength was demonstrated. This was achieved with a novel beam combining and shaping technique using COTS diode lasers. The fiber-coupled output corresponds to a Beam Parameter Product (BPP) of 18 mm-mrad and is the lowest BPP kW-class direct diode laser yet reported. The laser has been used to demonstrate laser cutting and welding of steel sheet metal up to 6.65 mm thick. Higher brightness fiber-coupled diode lasers, including a module with 418 W of power coupled to a 100 μm, 0.15 NA fiber, have also been demonstrated.

We report on the performance of a 100 W, 105μm, 0.17 NA (filled) fiber-coupled module operating at 976 nm. Volume holographic (Bragg) gratings are used to stabilize the emission spectrum to a 0.2 nm linewidth and wavelengthtemperature coefficient below 0.01nm/°C with virtually no penalty to the operating power or efficiency of the device. The typical fiber coupling efficiency for this design is >90%, enabling a rated operating efficiency of ~50%, the highest reported for a 100W/105μm-class diode pump module (wavelength stabilized or otherwise).

We present an overview of rare-earth doped heavy metal oxide and oxy-fluoride glasses which show promise as host materials for lasers operating in the 2-5 μm spectral region for medical, military and sensing applications. By engineering glass composition and purity, tellurite and germanate glasses can support transmission up to and beyond 5 μm and can have favourable thermal, mechanical and environmental stability compared to fluoride glasses. We discuss techniques for glass purification and water removal for enhanced infrared transmission. By comparing the material properties of the glass, and spectroscopic performance of selected rare-earth dopant ions we can identify promising compositions for fibre and bulk lasers in the mid-infrared. Tellurite glass has recently been demonstrated to be a suitable host material for efficient and compact lasers in the ~2 μm spectral region in fibre and bulk form and the next challenge is to extend the operating range further into the infrared region where silica fibre is not sufficiently transparent, and provide an alternative to fluoride glass and fibre.

Quantum cascade lasers are finding rapid acceptance in many defense and security applications. Our new multispectral laser platform providing watt-level outputs near 2.0 μm, 4.0 μm and 4.6 μm in continuous wave regime at room temperature. Individual lasers are spectrally beam combined into a single output beam with excellent quality. Our rugged, compact (11 × 10 × 6.5 inches), and highly reliable, air-cooled multispectral laser platform is already finding acceptance at system level. Our uncooled devices produce > 2W at 4.6 μm and >1.5W at 4.0 μm at room temperature, and maintain watt-level output at 67°C with real wallplug efficiencies >10%. Finally, all of our QCLs undergo 100-hour pre-delivery burn-in and pass shock, vibration, and temperature testing according to MIL-STD-810G.

Transparent sesquioxide ceramics, e.g. Y₂O₃ and Sc₂O₃ are being developed as alternatives to yttrium aluminum garnet (YAG) for high-power solid-state laser systems. In this work, we present the synthesis of these sesquioxide nanopowders by precipitation techniques and the subsequent processing of these nanopowders into sub-micron transparent ceramics using a modifying two-step sintering approach. These transparent ceramics exhibited equivalent transparency to that of analogous single crystals. The microhardness and fracture toughness of the modified two-step sintered ceramic exceeded those of conventionally sintered ceramic by 25% and 70%, respectively.

Polycrystalline ceramics offer a number of advantages relative to single crystal materials such as lower processing temperatures, improved mechanical properties, and higher doping levels with more uniform distribution of dopants for improved laser performance. Ceramic YAG (Y₃Al₅O₁₂) and rare earth sesquioxide (RE₂O₃) fibers promise to enable a number of high power laser devices via high thermal conductivity and higher allowable dopant concentration; however, these materials are not currently available as fine diameter optical-quality fibers. Powder processing approaches for laser quality polycrystalline ceramic fibers are in development at AFRL. Current processing techniques will be reviewed. The effects of a number of processing variables on the resulting fibers as well as preliminary optical characterization will also be presented.

Laser performance measurements (quasi-CW) were made of various Nd-doped SCHOTT catalog laser glasses: LG-680, LG-750, LG-760, LG-770, APG-1, and APG-2; all but the first, a silicate, are phosphate glasses. Nominal Nd³⁺ doping was approximately 3 × 10²⁰ ions/cm³. An end-pumped, laser diode geometry was used and input powers, pump pulse length, and pump rep-rates were kept low to avoid thermal lensing (4 W, 1 msec, and 0.1 Hz, respectively). As expected, the phosphate glasses performed better than the silicate glass. Slope efficiencies ranged from 25% for LG-680 up to nearly 33% for LG-760. APG-1, designed for high rep-rate, high-power systems, performed nearly the same in this particular configuration as glasses designed for high-energy applications (e.g., LG-770).

The noise power spectrum of solid-state lasers - including fiber lasers - exhibits a characteristic peak at the relaxation oscillation frequency. The tails associated with this peak extend to neighboring spectral ranges and may increase the noise level above acceptable limits in applications using weak signals. One of the key factors to reduce the relative intensity noise (RIN) amplitude is a low loss laser resonator. We describe a method to ultimately reduce the intensity noise in single frequency phosphate fiber lasers by minimizing intra-cavity losses caused by fusion splices between fibers made of different materials. Conventional fiber Bragg gratings written in silica fibers have been replaced with gratings written in phosphate glass fibers. The quality of the intra-cavity fusion splice has been improved due to material similarity. All-phosphate fiber laser devices have been built and tested utilizing the new gratings. The results show relative intensity noise amplitudes that are very similar to those of conventionally fabricated devices. Challenges in the grating writing process are currently preventing the new devices from surpassing their commercial counterparts in terms of performance. However, this type of all phosphate glass fiber lasers may ultimately lead to a new generation of commercial single frequency fiber lasers with improved intensity noise performance.

Multiple ground and airborne vehicles could share common and multifunctional laser modules. The host system constraints and requirements have similarities making a laser modular concept interesting. Among the desired functions, the core ones are the designation and the rangefinding capabilities. A diode pumped laser source at 1μm with a switchable OPO stage for wavelength conversion fully satisfies the designation and rangefinding tasks. Over the last years, CILAS has developed the key technologies for the improvement of the main system parameters with the imperative constraints to be International Traffic in Arm Regulations Free (ITAR Free). Particularly, this novel architecture avoids thermo electric cooler (TEC) generally used to stabilise the wavelength of the laser diode pump source within the entire operational thermal range.

While conventional Raman Spectroscopy (RS) has predominately used fixed wavelength cw lasers, advanced Raman spectroscopic techniques such as Stimulated Raman and some types of Raman Imaging typically need pulsed lasers with sufficient energy to induce the Raman process. In addition, pulsed lasers are beneficial for the following Raman techniques: Time Resolved Raman (TRR), Resonance Raman (RR), or non linear Raman techniques, such as Coherent anti-Stokes Raman spectroscopy (CARS). Here the naturally narrower linewidth of a ns pulse width laser is advantageous to a broader linewidth ultrafast pulsed laser. In this paper, we report on the development of a compact, highly efficient, high power solid-state Ti: Sapphire laser ideally suited for many Raman spectroscopic techniques. This laser produces nanosecond pulses at kHz repetition rates with a tunable output wavelength from ~1 micron to ~200 nm and pulse energies up to 1 mJ. The narrow bandwidth of this laser (<0.1cm^-1) is ideally suited for applications such as Laser-induced fluorescence (LIF) measurement of OH free-radicals concentrations, atmospheric LIDAR and Raman spectroscopy. New KBBF and RBBF deep ultraviolet (DUV) and vacuum ultraviolet (VUV) crystals are now available that enable direct doubling of the SHG output of these tunable Ti: Sapphire lasers to directly achieve wavelengths as short as 175 nm without the need to generate the 3rd harmonic and utilize frequency mixing. This results in a highly efficient output in the DUV/VUV, enabling improved signal to noise ratios (S/N) in these previously difficult wavelength regions. Photonics Industries has recently achieved a few mW of power at 193nm with such direct doubling crystals.

Precision Photonics Corporation (PPC) has developed high Laser Damage Threshold (LDT) coatings for the important 2-3μm spectral region. Accurate information for both LDT and absorption for such coatings is sparse and often unreliable, especially when compared to the huge amount of information for these parameters in the 1μm spectral region. The goal of this effort is to provide useful, accurate information for high power/energy coatings, given the limited LDT and absorption testing capabilities for the 2-3μm region. In this paper, we present data for 2μm pulsed LDT, 2μm absorption, 3μm pulsed LDT, and Continuous Wave (CW) LDT data.

Ultrafast Bandgap Photonics is discussed as an alternative technology for laser-based Directional IR Counter Measures (DIRCM). Ultra-fast laser is capable of providing fundamentally different type of countermeasure which is able to counter all generations of heat-seeking missiles. Ultrafast Bandgap Photonic technology is compatible with existing laser based DIRCM pointing systems as it requires much less energy per pulse and peak power than damage inducing systems. A foundation of ultra-fast technology is its ability to remotely alter seeker characteristics. In this paper, we will consider the effects caused by relatively low energy per pulse ultra-fast and, to some extent, fast lasers.

It is an effective approach to obtain high-power laser output by spectral beam combining (SBC) technologies. The power of the output beam increases with the increasing of the number of wavelength channels. However, that makes the traditional SBC system very huge for achieving high power laser output. In this paper, a simple SBC system based on the superimposed Reflective Volume Bragg Grating (RVBG) is proposed to reduce the scale of the SBC system. Two structure models of the superimposed RVBG - the superimposed RVBG with the same period and the superimposed RVBG with different period are analyzed and compared by using the rigorous coupled wave analysis, and their applications for SBC system are discussed. Numerical results show that the superimposed RVBG are easy to be fabricated and have the potential to combine multiple lasers with one volume. The superimposed RVBG with different period can achieve high diffraction efficiency simultaneously for each grating with small slant angle divergence, and is convenience to combine two beams with small spectral separation.

A compact micro-oscillator incorporating a dual-bounce, grazing incidence gain module with a folded resonator cavity is presented. The gain module, previously developed for Nd:YVO4, is embodied in highly doped ceramic Nd:YAG to generate improved Q-switch performance while maintaining localized pump absorption. The cavity design utilizes a doubly folded optics path around the gain crystal to increase the intra-cavity mode for a more optimum overlap with the pump light volume produced by standard lensed laser diode bars. A modified CS-package diode mount is developed to facilitate the reduced size of the oscillator without sacrificing the ability to use a high-energy, side-pumping arrangement. The oscillator is combined with a high gain, high energy extraction VHGM amplifier to generate a transmitter source on the order of 50 mJ. Cooling for both the oscillator and amplifier modules is provided via a conductive path through the base of the package. Both devices are mounted on opposite sides of a phase-change cooling reservoir to enable self-contained, burst-mode operation. Beam shaping of the oscillator output, in preparation for injection into the amplifier, is contained in a small cut-away path on the reservoir side.

This work demonstrates the modeling process of calculating coupling coefficients of first-order distributed feedback (DFB) semiconductor lasers, operating on transverse electric modes in the near-infrared (NIR) spectrum range. Optical waveguides are common structures in semiconductor lasers. The structure has dielectric layers and a metal grating layer. The interface between the metal layer and its neighboring dielectric layer has a sinusoidal corrugated geometry. Coupling coefficients are important parameters when analyzing laser performance. To calculate the coupling coefficient of a shiny-metal-grating waveguide, an electromagnetic model is constructed by truncated Floquet-Bloch formalism (TFBF). Ray optics technique is also used to calculate the coupling coefficients. These two methods have close results.