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Sensors and Electron Devices Directorate Research Areas

Solid-State Science

 

High Power Solid-State Laser Science and Technologies

Advisor: Dubinskiy, Mark; Merkle, Larry Dean

Key words: laser material, solid-state Laser, high power laser, ceramics, phase conjugation, heat spreader, eye safe

Research is being pursued on enabling technologies for high power solid-state lasers to meet the needs of the Army and the other armed services. These lasers are more rugged and compact than gas lasers, but have not been scaled to sufficiently high powers while maintaining good beam quality. We are investigating technologies for scalable gain media, thermal management, and beam quality improvement. These include ceramic gain media, which are as good as single crystals in most regards, are mechanically stronger, and can be scaled to larger sizes. We are pursuing the use of these materials and others at cryogenic temperatures, where key thermal and optical properties are much improved over room temperature. We are particularly interested in laser operation at wavelengths near 1.6 microns in Er-doped solids, since this wavelength range offers much improved eye safety, and where ongoing advances in diodes lasers offer the potential for greatly improved efficiency and reduced thermal distortion. Other gain media of interest are fibers, which offer considerable beam quality and efficiency advantages but require innovative designs to enable sufficient power scaling. We are also investigating special materials and geometries to promote heat removal from laser gain media and to further improve beam quality, beam correction techniques based on stimulated light scattering (Brillouin and Raman).

Our laboratories have a range of laser and spectroscopic tools for these studies. These include several types of diode lasers and arrays for efficient pumping of laser materials and a range of homemade laser cavities to test materials and thermal management approaches. We also have up-to-date spectrometers for absorption and emission spectroscopy, and cryostats for both laser and spectroscopic studies as a function of temperature.

References
Newburgh GA, Dubinskii M, Merkle LD: Electronics Letters 43: 286, 2007
Dubinskii MA, Merkle MD: Optics Letters 29: 992, 2004

Atom Chip Research

Advisor: Golding, William Michael

Key words: atom chip, bose condensate BEC, Laser cooling, Magnetic trapping, Quantum sensors, atomic physics atom interferometry, mems, quantum information

We are interested in exploring the potential of atom chip devices and demonstrating these potentials experimentally. Both theoretical and experimental candidates are welcome. Our laboratory is currently developing an experimental system for the study of Rb Bose condensates on arbitrary atom chip devices. We are working towards the complete development of miniature atom interferometric devices. We are interested in MEMS construction of atom chip devices, cold atom manipulation, quantum optics, quantum information, and experimental atomic physics.

Nonlinear Optical Materials for Nonlinear Transmission

Advisor: RC Hoffman

Key words: nonlinear optics, nonlinear materials

We are interested in investigating and utilizing a variety of nonlinear optical behaviors for Army applications. Research focuses on self-induced nonlinear behavior in the visible and the near infrared, from CW to femtosecond and involves such phenomena as reverse saturation, self-focusing/de-focusing, two-photon absorption, and the Pockels effect. In the area of nonlinear materials, we are interested in developing and understanding materials that exhibit large nonlinear transmission. Promising material candidates are characterized and the nonlinear parameters are derived using Z-scan analysis and pump-probe measurements. By modeling the beam propagation along with the light-matter interaction, we can study the mechanism that gives rise to the nonlinearity. In some cases, this knowledge allows further refinement of the material to exploit the nonlinear process for applications involving nonlinear transmission. Various materials have been and are currently being investigated including dyes, highly conjugated organic molecules, metallorganic compounds, composites, carbon black suspension, C60/C70, easily damaged windows, polymers, glasses, and semiconductors.

Integrated Optics for Communications and Phased Array Antenna Control

Advisor: W Zhou

Key word: optical communications, optical communications, Waveguides, Antennas, Large-scale integration (electronics)

Sophisticated functionality can be achieved with monolithic integration of waveguide couplers, delay lines, modulators, and detectors. For example, we are investigating a time integrating delay line for microwave phased array antenna beamforming. Fabrication process simplicity and compatibility is significant to the realization of such integrated optical architectures. We are developing InP based, monolithically integrated, waveguide couplers, splitters, amplifiers, and modulators for photonic integrated circuits using selective area epitaxial growth. We are also studying novel opto-electronic devices such as photonic bandgap devices, micro-resonator devices, and optical MEMS devices. Sophisticated RF photonic systems can be built by integrating these novel devices with integrated waveguide circuits.

This research focuses on the design, fabrication, and characterization of novel waveguide architectures for applications in communication (de)multiplexing and phased array antenna control. Key technical issues include modeling and fabrication of broadband (>20 GHz) novel RF-photonic devices, as well as developing the integration technology of these photonic devices. Our objective is to demonstrate a monolithic module that can perform sophisticated functionality for RF photonic systems.

Growth and Analysis of Organometallic Vapor Phase Epitaxial III-Nitride Devise Structures

Advisor: KA Jones

Key words: III-Nitrides, Organometallic vapor phase epitaxy, GaN/AlGaN HEMTs, Silicon Carbide, Ion implant activation

Device structures that require thin layers with abrupt junctions are usually grown by organometallic vapor phase epitaxy (OMVPE) or molecular beam epitaxy. Although OMVPE is more cost effective and more amenable to selective area epitaxy, its growth is more complex because it involves surface chemical reactions and its layers are often less uniform. We are currently growing the III-nitrides with application to GaN/AlGaN HEMT devices and encapsulates for ion implanted GaN and SiC devices. Pendeo-epitaxial device structures are grown to measure the effects of defects on device properties by comparing the device characteristics of HEMTs fabricated from pendeo-materials with those fabricated from material grown in the usual way.  To improve the quality of device structures, we are analyzing the grown structures with double crystal x-ray diffraction, Rutherford backscattering spectroscopy, transmission electron microscopy, secondary ion mass spectroscopy, transmission electron microscopy, secondary ion mass spectroscopy, scanning Auger spectroscopy, scanning electron microscopy, and photoluminescence and photoreflection spectroscopy. These results are correlated with the electrical Hall, CV, and deep-level transient spectroscopy measurements and the device characteristics.

Quantum Well Infrared Technology

Advisor: KKChoi

Key words: Nanosensors, Voltage tunable sensors, Photonic crystal ICs, Spectrometers, Focal plane arrays

Based on the mature III-V material capability, quantum well infrared technology has been developed rapidly. Large format long wavelength focal plane arrays up to 1024 x 1024 pixels have been demonstrated in our laboratory. Even larger format FPAs with advanced detection functionality are being developed. Research opportunities range from basic physics to array production and demonstration. In particular, we are developing fabrication processes to produce FPAs with 2048 x 2048 pixels, which will be integrated with advanced features such as voltage tunable two-color detection, adaptive multicolor detection, and polarization-sensitive detection. To achieve these capabilities, fundamental physics, such as hot-electron dynamics, electron transfer in QWs, QW band structures, and near-field electromagnetic phenomena, are currently being studied.

Besides these near- and mid-term projects, long-term research projects are also of interest. In the nanosensor project, research is conducted to fabricate nanoscaled sensors and to study their optoelectronic properties. The objective is to produce the smallest functioning infrared sensor for molecular electronics. In the photonic crystal QWIP integrated circuit project, photonic bandgap structures are fabricated into the QWIP materials. The embedded QWIP detectors are used for the study of the wave guiding and scattering effects of photonic crystals. The objectives are to integrate the ICs with quantum cascade lasers for free space transceiver applications and for chemical sensing applications. Research opportunities in these areas include nanofabrication, low-dimensional physics, electromagnetic phenomena in photonic crystals, and device fabrication and demonstration.

References
Choi KK, et al: Applied Physics Letters 84: 4439, 2004
Choi KK, et al: International Physics & Technology 47: 76, 2005

Fabrication of Wide-Bandgap Semiconductor Devices

Advisor: KA Jones

Key words: Device fabrication, Wide band-gap semiconductors, Ion implant activation, Contact metallurgy, Metal contacts, Etching

Wide-bandgap semiconducting materials such as SiC, and GaN possess many intrinsic properties, which make them highly attractive for high-power, high-temperature, and high-power, high frequency device applications. These properties include high breakdown strength, high-electron-saturation velocity, high thermal conductivity, thermal stability, and (in the case of GaN/A1GaN) a wide direct bandgap. Recent advances in materials growth processes have spurred the development of new devices and related processing technologies, which are immature. In order to realize the full potential of these materials, we must develop suitable processes for implanting, etching, contacting, and passivating these devices.  SEDD facilities consist of microwave, ECR, and RF plasma-assisted etching/deposition; metallization; and photo/e-beam lithography. Materials characterization capabilities include secondary ion mass spectrometry, Auger electron spectroscopy, x-ray diffraction, and backscattering spectroscopy. Other capabilities include dc and rf electrical parameter analysis, pulsed power testing, and optical characterization.

Novel Semiconductor Structures and Devices for Optoelectronics, Photonics, and Optical Signal Processing

Advisor: P Shen

Key words: novel semiconductors, quantum wells, optical signal processing, crystal superlattices, photonics
optoelectronics, heterostructures and heterojunctions, molecular beam epitaxy

New classes of solid-state, quantum-well devices offer the possibility of ultrahigh-speed (picosecond) switching and ultrahigh-frequency (>100 GHz) operation for diverse microelectronic and photonic applications. SEDD is studying the properties of strained layer semiconductor structures that promise novel electronic and optical properties. In addition, we are investigating spatial light modulators, waveguide modulators, waveguides, lasers, and high-speed electronics. These heterostructures are designed and processed into prototype test structures to demonstrate proof-of-principle devices.

We have complete facilities for optoelectronic device design, fabrication, and testing. Research focuses on (1) studying molecular beam epitaxy for novel semiconductor heterostructure growth for higher performance and new functionality, and (2) developing sophisticated semiconductor device-processing technology for nanoscale device fabrication. Specific technology areas consist of ultrahigh-resolution electron-beam lithography, magnetron-ion etching, electron-cyclotron resonance, plasma-enhanced chemical vapor deposition of dielectrics, and metal contact formation. Microanalytical test facilities are available for semiconductor structure characterization, including secondary ion mass spectrometry, scanning electron microscopy, transmission electron microscopy, Rutherford backscattering, AEM, glow discharge mass spectroscopy, photoreflectance, photoluminescence, and Raman spectroscopy. Facilities are also available for DC, RF, and optical testing of devices and circuits. Research opportunities exist in the areas of epitaxial materials growth; and electronic and photonic device design, modeling, fabrication, and characterization. Emphasis placed on technology related to photodetectors, lasers, high-electron mobility transistors, and mesoscopic devices.

Physics of Semiconductor Microstructures

Advisor:SI Rudin

Key words: heterostructures and heterojunctions, Optical properties, Semiconductors

The following areas of research are of interest to this program: (1) theory of optical properties of semiconductor quantum dots; (2) non-equilibrium dynamics of photo-excited carriers in wide-band-gap semiconductors; (3) dephasing of optically excited quantum states in semiconductor heterostructures.  

References
Rudin S, Reinecke TL, and Bayer M, Physics Rev. B 74, 161305, 2006

III-V Optoelectronics for Signal Processing

Advisor: GJ Simonis

Key words: optoelectronics, compound semiconductors, quantum wells, optical signal processing, crystal superlattices, microwave electronics, optical waveguides, molecular beam epitaxy

The primary objective of this research is to explore III–V optoelectronic processes and components that are applicable to optical signal processing, particularly those based on quantum wells and superlattices. Experiments involve incorporating these structures into waveguide or vertical-coupling structures that are promising for the optoelectronic manipulation of information. Current research involves the integration of waveguide components into integrated optical circuitry and the improvement of waveguides, phase and amplitude modulators, splitters, and cross-overs. Furthermore, we are studying Fabry-Perot vertical-cavity structures, which offer the potential for two-dimensional arrays of active elements that can be used for the two-dimensional entry and manipulation of information on free-space propagating optical beams. In-house fabrication facilities include molecular beam epitaxy material growth, computer-aided design mask generation, lithography, etch processing, focused ion beam milling, and clean rooms. A variety of lasers, spectrometers, optical tables, micropositioners, detectors, electronics, computer interfaces, and other components allow us to rapidly assemble and conduct our experiments.

We are also applying laser heterodyne and optoelectronic means of phase and amplitude control to provide optoelectronic generation, control, and distribution of microwaves from dc to 100 GHz. Conversely, optical heterodyne interferometry provides us with a very sensitive measurement technique for characterizing the basic optical properties of these structures. We have a wavelength-tunable titanium-sapphire heterodyne interferometer.

Optical Studies of III-V Semiconductor Materials and Device Structures

Advisor: P Shen

Key words: compound semiconductors, optical properties, photometry, raman spectra, heterostructures and heterojunctions, optical waveguides, semiconductor switches, novel semiconductors

Optical techniques (both CW and time resolved) such as photoluminescence, Raman spectroscopy, and modulation spectroscopy, are being used to study the physics and materials properties of semiconductor heterostructures and devices. Research focuses on (1) the effect of strain on valence band and other strain-induced properties; (2) band mixing effects; (3) the dynamics of carrier transport, carrier relaxation, exciton dephasing, and relaxation in strained systems; (4) applications of strained systems in novel optoelectronic devices; and (5) electric/piezoelectric field effects and their optical detection. Emphasis is also placed on other structures that may lead to device applications, including light modulators, optical waveguides, lasers, high-power optical switches, and infrared detectors. Resources in our laboratory include CW, nanosecond, and femtosecond lasers; high-resolution spectrometers; and CW and time-correlated detecting systems. Research opportunities include basic physics studies and device design, testing, and modeling.

Infrared Cascade Laser Development

Advisor: RL Tober

Key words: cascade infrared lasers, optoelectronics, molecular beam epitaxy, communication lasers, electronics

This research program focuses not only on the design, growth, characterization, and applications of infrared (IR) cascade lasers, but also on gaining knowledge of the fundamental physical properties that affect their performance. The goal of this work is to develop efficient lasers for use in chemical detection, free space communication, medical, and IR-countermeasure applications. Research opportunities exist for widely ranging topics such as molecular beam epitaxy growth, device design and fabrication, electronics, theoretical analysis, and even application engineering. Recent studies have focused on laser loss mechanisms and thermal characteristics, and the development of novel lasers designs.

References
Suchalkin S, et al: Applied Physics Letters 88(3): 031103, 2006
Kisin MK, et al: Applied Physics Letters 85(19): 4310, 2004

Semiconductor Lasers, Detectors, and Optoelectronic Integration

Advisor: WH Chang

Key words: semiconductor lasers, quantum wells, heterostructures and heterojunctions, optical signal processing

Discrete semiconductor lasers and detectors are key elements in optical analog and digital transmission systems. Research is in progress to optimize such devices for high-speed operation and optoelectronic integration. As discrete components, current investigations center on using strain and strain-compensated quantum confined structures for low-threshold, high-bandwidth lasers. PIN detectors at both 0.85 mm and 1.3 mm wavelengths are also being grown and fabricated in-house.

Both discrete projects are related to concurrent work on optoelectronic integration. Two particular areas are (1) integrated emitters and detectors for radio frequency analog links and (2) arrays of emitters and detectors for optical interconnects and more generically parallel optical signal processing. For the latter area, we use a novel heterostructure arrangement that allows for concurrent fabrication of both lasers and field-effect transistors using a single epitaxial growth sequence. To be successful, such approaches must demonstrate a clear viability and performance advantage over other alternatives such as hybrid bonding. Opportunities exist to continue this research at a discrete device level and circuit level to provide “proof-of-principle” demonstrations of such technologies. SEDD has the capabilities to grow the initial material and fabricate through to finished circuits. As this type of technology progresses, simulation and modeling will be of increasing importance. The wider aspects of this project encompass user input regarding applications and collaboration with other organizations interested in similar projects.

Physics and Chemistry of Organic and Inorganic Luminescent Materials

Advisor: DC Morton

Key words: luminescence, electronic displays, doped crystals, inorganic, organic

Organic and inorganic luminescent materials are utilized in various display devices. Therefore, it is essential that we explore their optical, chemical, crystallographic, and electrical properties from a basic research viewpoint. For inorganic devices, we are interested in doping studies and characterization of wide band gap (WBG) materials and devices to establish donor/acceptor levels in the forbidden gap. The materiel properties such as crystallinity, film morphology, and doping concentration are correlated to device characteristics under different excitation types (i.e., cathode ray, electric field, photons). In addition, the carrier transport in these structures and devices is a key area of investigation. Another interest area includes identifying and assessing the physical effect of defects in the materials on the luminescent excitation and relaxation processes. For organic based devices, we are interested in similar material and device properties, including organic film formation, doping, carrier transport, and molecular structure. Cooperative research for both organic and inorganic device physics is being carried out with several universities on different materials, structures, and devices. In house, we have several deposition systems for thin-film device fabrication that include inorganic phosphors, dielectrics, and metals as well as systems dedicated to organic device fabrication, and for high-process temperature phosphor powder investigations. The laboratory is equipped with many characterization capabilities to study the material and device properties as a function of temperature from 10 K to 800 K. These techniques include pulsed and DC current-voltage characterization, trap state spectroscopy, Raman, AFM, Fourier-transform infrared, photoluminescence (DC to 2nsecs), electroluminescence, cathodoluminescence and others. This research will be done in collaboration with the microanalysis group at SEDD to provide the other materials characterization capabilities.

Novel Optoelectronic Photonic Devices

Advisor: W Zhou

Key words: photonics, optoelectronics, novel semiconductors, heterostructures and heterojunctions, quantum wells

We develop innovative optoelectronic devices (e.g., modulators, splitters, switches, amplifiers, and lasers) and radio frequency-photonic devices (e.g., infrared receivers, optical/microwave converters, photodetectors, and photo-receivers). These devices have applications into photonically controlled microwave systems, fiber-optic gyroscopes, collision avoidance systems, and biosensors.

This research and engineering development involves basic device and material physics studies, as well as prototype device design, modeling, fabrication, and characterization. The development program offers great potential for device and material characterization techniques, their maturation, and advancement. Current research includes aspects of design and characterization of novel strained semiconductor quantum well heterostructures to obtain polarization control, epitaxial growth techniques such as selective epitaxy and regrowth for the purpose of bandgap engineering, monolithic integration of high-speed photodetectors with active field-effect transistors, and monolithic integration of passive and active waveguide components.
SEDD has extensive facilities for material growth, fabrication, and optical and electrical characterization.

RF Perovskite Materials and Devices

Advisor: FJ Crowne, DM Potrepka

Key words: advanced RF field-tunable material, ferroelectrics, multi-ferroic, magnetoresistors, superconductor
field tunable material, bulk and thin-film material synthesis, pulsed laser deposition, temperature and frequency dependent electrical properties, variable true-time delay devices, field agile components for RF front-end technology

Opportunities exist within the area of RF perovskite material research and device development. Material and device research may focus on ferroelectrics, multi-ferroics, dielectrics, magnetoresistive, high critical temperature superconductors as well as other perovskites for RF applications.

Currently, this program emphasizes the development and use of field-tunable perovskite materials that are single-phase solid solutions and nearly temperature insensitive over the military specified temperature range (-50 to 100oC) for fabrication and development of low-cost, lightweight, low power-consuming field-tunable RF devices such as phase shifters and variable true-time delay devices for electronic scanning antennas. Some of our other device areas and interest include but are not limited to; frequency agile filters, electronic variable attenuators, and passive millimeter/microwave detectors. Materials efforts currently focus on further increasing the field-tunable response while further reducing the dielectric constant and microwave loss tangent of the material. Device efforts focus on developing designs for lowering driving voltages and insertion loss while providing a low-cost, plug and play architecture for RF phase shifters, true time delay devices as well as other RF tunable devices for electronic scanning antenna systems.

We fabricate thin-film perovskites using the excimer laser ablation system, which includes several chambers with multitarget holders for deposition of multilayers. Facilities exist for the fabrication by solid-state reaction of bulk ceramics, and for chemical, structural, and electrical analysis of materials. Analytic capabilities consist of secondary ion mass spectroscopy, Auger electron spectroscopy, transmission electron microscopy, scanning tunneling microscopy, scanning electron microscopy, energy-dispersive spectroscopy, and x-ray diffraction spectroscopy. Device research is supported through extensive computer-aided design facilities, lithography, processing and packaging laboratories, and numerous electrical characterization facilities.

 

Magnetic Resonance Force Microscopy

Advisor: DD Smith

Key words: magnetic resonance, Magnetic fields, microscopy, magnetic Resonance Imaging

Magnetic resonance force microscopy (MRFM), a recent technical approach used to detect magnetic resonance, operates mechanically instead of electronically. MRFM promises to deliver magnetic resonance imaging (MRI) of three-dimensional inhomogeneous objects with Å resolution and one proton sensitivity. The high resolution and sensitivity make it possible to determine the structure of large biologically relevant molecules. In principle, an x-ray can do this; however, it usually fails because the required crystals are difficult to form. Our interest in MRFM is with proton containing organic materials, especially thin films and single cells.

The mechanical detection method for one proton uses a 30-nm diameter magnet mounted on the end of a silicon cantilever 20-nm thick, 1-micron wide, and 50-microns long. The tiny magnet applies a magnetic field gradient to the spin system under investigation. The spin exerts a force on the cantilever through its interaction with the magnetic-field gradient. Irradiation of the spin system with radio frequency magnetic fields at the spin system’s resonance frequency causes the spins to oscillate back and forth. The oscillating magnetic moment moves the cantilever. Recent accomplishments include (1) observation of 4 K MRFM on GaAs at high magnetic fields, (2) observation of 4 K MRFM on optically pumped GaAs, and (3) design and construction of the next-generation MRFM system for organic materials with 3D imaging ability.

References
Lee E. Harrell, Kent R. Thurber, Doran D. Smith: Journal Applied Physics, 95: 2577, 2004
Kent R. Thurber, Lee E. Harrell, Doran D. Smith: Journal of Magnetic Resonance, 162: 336, 2003.
Kent R. Thurber, Lee E. Harrell, Doran D. Smith: Journal of Applied Physics, 93: 4297, 2003.

Bioinspired Devices and Sensors

Advisor: PM Pellegrino

Key words: biomimetic, biosensor, photonics, electronics, biotechnology, sensors, bioengineering, biophotonics, bioelectronics

The objective of our research is to investigate biologically-inspired routes and advanced biotechnology for improved performance and fabrication ability of photonic/electronic devices and sensors. Natural evolution could be considered the pinnacle of engineering science. Mimicking or understanding the unique processes, structures, and phenomena generated by this natural engineering could shed new insight into physical limitation imposed by classical methodologies. The combination of modern biotechnology, which imparts us with the ability to manipulate organisms, cells, and DNA and bioengineering, could provide researchers a new paradigm for development of revolutionary photonics, electronics, organic-electronic hybrids, and sensors. In an effort to capitalize on these advances, targeted investigations will be conducted on the following areas: biosensors to either sense biology or sense with biology, biomimetic sensors, photonic and electronics devices which replicate/mimic or harness biology, and bioelectronics built from biological structures or assembled/enabled by biological structures. These efforts include the development of new characterization methods (spectroscopy and metrology) geared specifically to organic or organic-inorganic hybrid materials. Practical use of advanced biotechnology for electro-optic devices and sensors is inherently a cross-disciplinary pursuit. Large effort must be applied to find advantageous biological-inspired routes for the respective technology areas and will include input from classical technical disciplines (biology, chemistry, physics, and engineering).

Low-quantum-defect diode-pumped Er-doped fiber lasers and rod lasers

Advisor: Jeffrey O. White

Keywords: Erbium laser, Fiber laser, Solid-state laser, Phase conjugation, Brillouin scattering, Beam combining, Eye-safe, Diode pumping

The general topic is research into new science and technology that will be useful in the next generation of high power fiber lasers and high power solid state lasers at wavelengths greater than 1.6 µm.  Our approach usually involves low-quantum-defect laser diode pumping.

One specific project is to design and build a high average power Erbium fiber laser with beam quality close to the diffraction limit.  Stimulated Brillouin scattering (SBS) limits the power scaling of conventional fiber amplifiers, because it can reflect ~100% of the incident wave when the product of gain, intensity, and effectiver length reaches the level gIL~30, where I is the intensity within the Brillouin linewidth.  The approach we propose is to use a large mode area (LMA) fiber in a highly  multimode configuration.  The diffraction-limited quality will be recovered through phase conjugation or beam cleanup, via SBS in a separate fiber.   

Another project is the engineering of solid-state laser rods to increase the power output.  Multi-kilowatt rod lasers designed for end-pumping by stacks of diode bars are typically polished on the barrel surface, to waveguide the pump. This inevitably leads to parasitic oscillations, at the laser wavelength, known as whispering gallery modes (WGM), due to total internal reflection at the barrel surface.  For YAG immersed in cooling water, the index difference is so high that the WGM occupy 50% of the rod volume.  Suppressing the WGM can theoretically lead to a doubling of output power. 

Several means for suppressing the WGM will be explored.

References:
1.  J.O. White, M. Dubinskii, L.D. Merkle, I. Kudryashov, and D. Garbuzov,
“Resonant pumping and upconversion in 1.6µm Er3+ lasers,”
Journal of the Optical Society of America B 24, 2454-2460 (2007).

2.  B. Steinhausser, A. Brignon, E. Lallier,  J.P. Huignard, and P. Georges,
"High energy, single-mode, narrow-linewidth fiber laser source using stimulated Brillouin scattering beam cleanup," Optics Express 15, 6464-6469 (2007).