Analytical Instrumentation : Lasers

Analytical Instrumentation Portfolios


Single-Crystal Halide Perovskite Nanowires with Superior Performance

Metal halide perovskite-based material is emerging as a “superstar” semiconductor material for cost-effective photovoltaic applications. UW–Madison researchers have developed a practical solution growth method for producing single-crystal perovskite nanowires with superior material quality and lasing performance.

Specifically the new method is based on a facile process of low-temperature dissolution of a metal precursor film in a cation precursor solution, followed by recrystallization to form single-crystal perovskite nanostructures such as nanowires, nanorods and nanoplates. Diverse families of metal halide perovskite materials with different cations, anions and dimensionality with different properties can be made to enable high-performance device applications.

More Efficient Semiconductor Lasers

UW–Madison researchers have taken a new approach and developed QCLs configured for symmetric longitudinal mode (single-lobe beams) with no loss in efficiency. Instead of relying on phase shifters, the new lasers work by suppressing undesired antisymmetric longitudinal modes.

The lasers are made of layers of cladding, metal (such as gold or silver) and indium phosphide-based semiconductor material. The interface of the metal and semiconductor layers forms a corrugated, second-order distributed feedback grating, which absorbs the undesired antisymmetric longitudinal modes. This configuration eliminates the need for cleaved facets.

Simplified Anisotropic Graphene Conductor Emits Terahertz Radiation

UW–Madison researchers have designed an electromagnetic radiation device that can generate THz frequencies using an electrically conducting thin film.

The film is made of graphene layered over a substrate patterned into stripes of two alternating materials, such as germanium and silicon dioxide. This causes the charge carrier mobility across the plane of the thin film to vary periodically. When voltage is applied to the film, electrons flow through, changing velocities and giving rise to a spatially varying electric field. This produces electromagnetic radiation from the exposed surface of the film as the electrons pass through.

The graphene layer can be grown or deposited directly on the patterned substrate using known nanomembrane or thin-sheet transfer techniques.

More Efficient and Reliable High Power Quantum Cascade Lasers

UW–Madison researchers have developed a design to reduce threshold-current density and virtually suppress electron leakage using certain multiquantum well structures in the active regions of QCL devices. The structures are designed to work reliably over long periods of time at high efficiency and power (i.e., watt range) during quasi-continuous or continuous wave (CW) operation.

Known methods may be used to fabricate the semiconductor structure and laser devices and to form the electron injector, active region and electron extractor. The active region features a series of quantum wells and barriers of various alloy compositions. The energies of the first and second barrier in the active region are less than the third barrier.

Smoother Waveguides for More Efficient Nonlinear Frequency Conversion

UW–Madison researchers have developed a method for fabricating OPGaAs two-dimensional semiconductor-based waveguides having extremely low layer-interface roughness.

The structure is grown on a template using standard techniques and comprises a core sandwiched between upper and lower cladding layers. The layers have different, periodically arranged crystalline orientations. The surfaces between each layer undergo chemical polishing and isotropic etching that can be done in situ. A high-refractive-index ridge projects above the upper cladding layer and runs along the direction that light propagates. Known lithographic techniques and a combination of wet and dry etching create straight, smooth sidewalls.

Steering and Tuning Lasers Formed by Nanoscale Microtubes

UW–Madison researchers have developed semiconductor microtube lasers that are wavelength-tunable and can be steered when an electromagnetic field is applied.

The microtube is a heterostructure of various group III/V alloys integrated for different purposes. The structuring involves three essential components: a strained layer to make the tube curl, an optically active lattice to emit laser light (interband or intersubband), and a grating structure to provide optical feedback. Thickness of the layers may range from five to 2000 nm.

Unlike existing lasers, the diameter of the microtube can be altered to produce different wavelengths of light. Through piezoelectric coupling or the addition of an insulating layer that leads to a change in lattice spacing, the tube can be made to expand or contract, corresponding to modulated emissions.

Additionally, the microtubes can be anchored in devices with electrodes that cause them to rise and tilt, steering the direction in which their light is given off.

New Method of Constructing a Quantum Cascade Laser with Improved Device Performance

UW–Madison researchers have developed a method to grow a QCL on compositionally graded metamorphic buffer layers. Unlike traditional QCLs that position the device directly on an InP or GaAs substrate, this method uses these substrates to grow the graded metamorphic buffer layers; this localizes dislocations and provides a platform with a larger lattice spacing on which to grow the QCL structures. Thus, the metamorphic buffer layers can be utilized as virtual substrates with a specified lattice spacing, opening up the palette of III/V alloys available for new device architectures and strain mitigation.

The researchers have developed a semiconductor structure comprising a GaAs substrate, a metamorphic buffer layer structure over the substrate and a quantum cascade structure over the metamorphic buffer layer structure. This QCL is characterized by its ability to emit light at 4.5 microns or less when under the influence of an applied electric field.

High-Power Quantum Cascade Lasers for Single, In-Phase Mode Operation

UW–Madison researchers now have developed a method to suppress oscillation of the array mode composed of coupled first-order elements modes, which will allow high-power quantum cascade lasers to perform at an optimal single in-phase mode. The structure of the laser array device includes an optical confinement structure comprising at least one layer of optical confinement material above and below the quantum cascade laser structure, a cladding structure and laterally spaced trench regions extending into the quantum cascade laser structure. The device is designed to produce an array mode composed of coupled fundamental lateral element modes meeting a lateral resonance condition that enables strong coupling between the “leaky waves” of all element regions. Two embodiments are possible.

The first embodiment requires an added metal absorption loss region layer above the element region and removes material from the element edges to induce losses in the transverse direction for the first-order mode.This induced loss is absorption of light by the layer deposited above the element region. The second embodiment inserts a diffraction grating inside or at the top of each element region over only a portion of the region. The gratings provide preferential feedback for array modes composed of coupled first-order element modes to assure high power in the desired in-phase mode. Either method removes the out-of-phase mode and allows optimal performance of a quantum cascade laser.

Nanoscale Electromagnetic Radiation Device Using Serpentine Conductor

UW-Madison researchers have developed a device for generating electromagnetic radiation by accelerating charges on a small serpentine conductor. This nanoscale device incorporates the strengths of both the FEL and BO methods of electromagnetic radiation generation to provide broadband, tunable radiation sources for portable applications.

The electronic device consists of a first and second electrical terminal and a nanoscale ribbon of conductive material providing a serpentine electrical path between the terminals. When charge carriers (electrons) are accelerated in the exposed curve portions of the ribbon, acceleration-induced electromagnetic radiation is emitted. The small dimensions of the ribbon constrain the charge carriers to a series of small-radius curves capable of producing electromagnetic radiation in the microwave range and potentially at light frequencies. The addition of resonant-cavity structures and/or optically active layers produces stimulated emission of coherent, laser-like radiation from a small device. Tuning of the radiation frequencies is possible by physically altering the dimensions of the structure or changing the electrical potential driving the charge carriers.

High Power, High Efficiency Quantum Cascade Lasers with Reduced Electron Leakage

UW-Madison researchers have developed a deep-well QCL in which the active region has barriers that are taller than those in the injector region and increase in height from the injection barrier to the exit barrier. This design significantly reduces the electron leakage, while maintaining the same laser-transition efficiency as in conventional QCLs. The threshold current at room temperature decreases by about 25 percent compared to that for conventional QCLs. The combination of low threshold-current values and virtually suppressed electron leakage leads to significantly higher front-facet or single-facet CW wallplug efficiencies (e.g., about 22 percent) at room temperature. As a result, QCLs operating at higher CW powers with higher CW wallplug efficiency as well as significantly better long-term reliability can be achieved.

High-Power Quantam-Cascade Lasers with Active Photonic Crystal Structure

UW–Madison researchers have developed a compact laser array device capable of generating high-power, coherent laser light at mid-infrared wavelengths by scaling the power of quantum-cascade (QC) lasers whereby an active photonic crystal (APC) structure is fabricated in the QC material. The combined APC-QC structure allows the laser device to emit diffraction-limited, stable beams from large apertures.

The compact quantum-cascade laser structure consists of one or more active cores, an optical confinement structure, a cladding structure and laterally-spaced trench regions extending through the structures. The structure has index steps an order of magnitude higher than in conventional structures. Quasi-continuous wave or continuous wave laser operations are desirable in many applications, but often are vulnerable to thermally induced variations in the dielectric constant. The APC-QC structure allows a device to operate as a quasi-continuous wave or continuous wave laser without thermally induced variations. Furthermore, the heat generated in the low-index regions can be effectively laterally removed by materials in the high-index regions.

Multi-Spectral Laser with Periodically Poled Crystal Mixer for Carbon Isotope Ratio Measurements

A UW-Madison researcher has developed a technique that uses a single crystal with three separate lasers to create a multi-spectral laser light source.  This set-up allows for a greater modulation range than the standard range for the crystal.  It also is capable of measuring the corresponding absorption lines of two species without requiring two crystals and four lasers or precise determination of the sample temperature.

Reducing the number of crystals and lasers drastically reduces the cost of the spectrographic device and is done by “back bending” the modulation curve of the PPLN crystal.  Three lasers of different frequencies illuminate the crystal to give two different output frequencies.  Nonlinear mixing occurs between the first and second input lasers and the second and third lasers, but not at the second frequency or a range of frequencies between the first and third inputs. 

Multilayer Si/SiO2 Semiconductors for Photoelectric Device Fabrication

UW-Madison researchers have developed an improved method for manufacturing quantum-well photoelectric devices from monocrystalline semiconductor layers.  The proposed invention aims to address the limitation of current technology with the use of Si charge carrying layers in between silicon dioxide (SiO2) barrier layers, allowing operation at room temperature and with wavelengths in the visible region.  The method used to fabricate these layers is similar to the previously developed technology except a different barrier material is used to promote electron confinement.

This method uses standard integrated-circuit deposition techniques and strain-symmetrization to produce superior virtual substrates upon which multiple layers are grown.  The process starts with the SOI substrate, a well characterized and developed technology commonly used in the integrated-circuit industry to fabricate Si computer chips.  The SOI base is thinned and smoothed using chemical or mechanical processes.  The alternating silicon/silicon dioxide layers then are grown on the SOI using standard deposition techniques.  The strain produced by the lattice constants of the two different materials is relieved by physically removing the layers from the SOI, creating a virtual substrate. 

The multiple growth and removal of the multilayer structure reduces the amount of defects in the crystal lattice, resulting in increased device power.  More layers can be grown on the virtual substrate to produce a component layer, but the number of grown layers is limited to reduce imperfections in the crystal lattice.  The multilayer structures then can be annealed to produce stacks of Si semiconductor of the desired thickness.  These semiconductors can be used to produce inexpensive and easily integrated quantum-well photoelectric devices, which have potential applications in chemical sensors, LEDs and all digital devices.

Multispectral Laser with Improved Time Division Multiplexing

UW-Madison researchers now have developed an improved, multi-wavelength, time-division multiplexed (TDM) laser capable of individually controlling multiple narrow wavelengths in separate time-division windows. Unlike the previous laser, this device uses a cavity that provides the same cavity length for each wavelength. To separate light into multiple wavelengths, it introduces a fixed time shift in the arrival of each wavelength at the output coupler as a function of the wavelength. It continuously cycles through the spectrally narrow wavelengths, spending a predetermined amount of time on each one. Specifically, the laser cavity holds the optical amplifier between a wavelength-dependent delay element (WDE) that temporally separates a multi-wavelength light pulse into discrete constituent monochromatic components, and a complementary wavelength-dependent delay element (CWDE) that temporally collects the monochromatic components after separation. This design reduces gain competition, simplifies the circuitry for controlling the amplifier and distinguishing the output pulses, and improves the consistency and control of the multiple monochromatic wavelengths.

Multi-Wavelength Mode-Locked Laser

A UW-Madison researcher has developed a mode-locked laser capable of generating multiple, discrete beams of light with different wavelengths from a single cavity. He has also developed a method of tagging the different wavelengths so the multiplexed beam can be measured by a single detector, which produces an output signal for each of the composite wavelengths.

In this device, multiple function generators are attached to a single laser. Each frequency provided by the function generators creates a different wavelength within the laser. The different wavelengths are then encoded by a single detector for analysis.

Intersubband Quantum Box Stack Lasers

A UW-Madison researcher has developed an intersubband-transition semiconductor laser with an Active-Photonic-Crystal (APC) structure that allows the coherent power of the laser to be scaled to at least 1 W while maintaining high (greater than 50 percent) wallplug efficiency. The semiconductor laser consists of an array of laterally-spaced ministacks of quantum boxes separated by a matrix of current-blocking material. Coupling a few quantum boxes in each ministack allows the laser to provide higher gain and more power than a semiconductor laser composed of an array of individual quantum boxes.

To increase the output power, the optically active core of the laser is enclosed in a laterally periodic dielectric stucture that creates an APC-type structure. The APC structure selects operation in a single spatial mode from large-aperture devices.

Continuous-Wave Laser Source for High Speed Spectroscopy

UW-Madison researchers have devised a simple and inexpensive laser-based spectroscopy approach that is similar to FTIR in principle; however, because it has no moving parts, it offers many advantages, including the ability to produce spectra every microsecond or faster. The laser is generally fashioned as a fiber laser, which is a laser cavity composed primarily of fiber optic cable. To measure spectra, the continuous-wave fiber output is directed at the test article and onto a single photoreceiver. The photoreceiver signal is then digitally processed to produce the desired spectra.

High-Performance Quantum Well Lasers with Strained Quantum Wells and Dilute Nitride Barriers

UW–Madison researchers have developed a GaAs-based multiple semiconductor layer structure for an improved optoelectronic device. The active region of the device includes at least one well layer composed of a compressively-strained semiconductor that is substantially free of nitrogen. Each well layer is disposed between two barrier layers composed of a nitrogen- and indium-containing semiconductor. This device is capable of generating light at wavelengths of 1.3 µm and higher.

High Efficiency Intersubband Semiconductor Laser

UW-Madison researchers have developed a highly efficient, quantum-cascade, intersubband semiconductor laser. This device is based on the successful deep quantum well active region structures previously described by the researchers (see WARF reference number P04199US). It uses strain-compensated GaAs-based stages, Bragg-type electron mirror regions and AlGaAs-based buried heterostructures to provide lateral heat removal. Unlike conventional QCL devices, the electron injector in this QCL is separated from the electron reflector, which significantly decreases electron backfilling and improves power-conversion efficiency.

Super-Continuum Ultraviolet Light Source with Single Stage Laser Drive

UW-Madison researchers have developed a fiber-coupled, broadband UV light source with approximately one million times the spectral radiance of conventional UV lamps. This UV supercontinuum source consists of a pulsed ultraviolet laser followed by a fiber-optic cable. It produces light that is laser-like, except that it possesses many colors rather than just one. To achieve supercontinuua, a particular relationship among properties including laser pulse duration and energy, laser wavelength and fiber dispersion, diameter and length must be met.

High Coherent Power, Two-Dimensional Surface-Emitting Semiconductor Diode Array Laser

The UW-Madison researcher has now developed a semiconductor laser that uses a variable periodicity, or chirped, grating. The grating works with the previous device to prevent the laser emissions from canceling each other out. The grating structure ensures single longitudinal-mode operation and can also be formed to act as a highly efficient selector of the in-phase array mode.

Intersubband Semiconductor Lasers That Operate Reliably at Room Temperature and in the Mid-Infrared

UW-Madison researchers have now developed a GaAs-based, quantum-cascade, intersubband semiconductor laser that suppresses virtually all carrier leakage, a feature that makes this device thermally stable during CW operation at room temperature and thus provides the first reliable semiconductor laser operating in the mid-infrared region. The device consists of very deep InGaAs quantum wells sandwiched between very high AlGaAs barrier layers, a structure that tightly confines injected carriers. This structure also prevents resonant tunneling between the X valleys of the surrounding barriers at high transition energies, a feature that also makes room temperature, mid-infrared emission possible in a GaAs device for the very first time.

Modeless Wavelength-Agile Laser

A UW-Madison researcher has developed an easily constructed modeless laser with a rapidly sweeping color that results in improved performance in many sensing applications. The laser changes its cavity length at a speed that prevents the formation of modes, resulting in a spectrally narrow, swept-wavelength light source that eliminates mode hopping. A pivoting mirror design provides the high rate of cavity length change.

Type II Quantum Well Optoelectronic Devices That Exhibit High Performance in the Mid-Infrared Region

UW-Madison researchers have developed an InP-based, type II quantum well laser device that exhibits high performance in the mid-infrared (2 to 5 micron) wavelength range. They designed a novel active region that includes electron quantum well layers composed of nitrogen-containing semiconductor materials, such as InAsN and InGaAsN. The active region also includes a hole quantum well layer composed of antimony-containing semiconductors, such as GaAsSb and InGaAsSb. By creating compressive strain in the hole quantum well layer alone, or by straining both the electron and hole quantum well layers, the researchers were able to generate laser light of the desired wavelengths.

High-Speed, Swept Frequency Spectroscopic System

A UW-Madison researcher has developed a wavelength-agile laser capable of rapidly scanning through a broad wavelength range, with superior light coupling and reduced light loss. It is particularly well suited to measure gas absorption in engines.

The invention consists of commercially available components that include an ultra-fast laser, a non-linear optical fiber and a frequency-spreading element. When these components are connected in series, the fiber optic cable receives a multi-frequency light pulse and spreads its frequency in time prior to transmitting it into a test cell. This approach significantly reduces losses involved in coupling light to the optic fiber and avoids the measurement of unwanted nonlinear processes. By directing the laser’s output through a test article of interest, the item’s properties can be determined by the recorded transmission spectrum.

Semiconductor Lasers with Doping Gradients in Optical Confinement Areas to Increase Laser Efficiency

UW–Madison researchers have developed a highly efficient, aluminum-free semiconductor light-emitting source that is particularly suited for high-power diode lasers of one-watt continuous wave (CW) output or higher. This device is grown on a semiconductor substrate and includes, in transverse section, an active region layer containing quantum wells, where the laser light is generated; optical confinement layers on either side of the active region layer; and cladding layers, one that is p-type doped and the other n-type doped, outside the confinement layers. The layers on either side of the active region layer confine the light emitted by the laser to the active region.

What makes this aluminum-free semiconductor device unique is the presence of a doping gradient in the layers surrounding the active region. Doping is heaviest in the confinement layers adjacent to the active region and quantum wells, and decreases toward the cladding layers. This doping profile creates an electric field that significantly increases the transport speed of injected carriers (i.e., electrons and holes), thereby reducing the non-ohmic voltage drop across the core of the device and greatly increasing laser efficiency. In addition, these doping profiles do not introduce a large free carrier absorption (FCA) penalty because the device is aluminum-free.

Two-Dimensional, Surface-Emitting, Semiconductor Diode Laser with High Coherent Power

A UW-Madison researcher has combined second order DFB and distributed Bragg reflector (DBR) grating structures with a phase-locked, anti-guided array to result in a two-dimensional, surface-emitting, semiconductor diode laser capable of two to three watts of output power during single-mode, single-frequency operation, and tens of watts of coherent power when scaled at the wafer level. The grating provides both feedback and light out-coupling, selects the desired in-phase array mode and can be designed to double the array-emitting aperture (from 100 to 200 microns) for increased power. The combination of anti-guided arrays with gratings also allows for scaling at the wafer level.

Narrow Lateral Waveguide Semiconductor Laser

UW-Madison researchers have now shown that a narrow lateral waveguide can be used in conjunction with a suitable transverse structure to achieve low optical power density and single mode operation in an edge-emitting semiconductor laser. Operation of the narrow lateral waveguide does not depend on a particular transfer structure, and can be combined with a transverse narrow waveguide, a broad waveguide or other structures that feature a large transverse spot size.

Type II Quantum Well Laser Devices

UW-Madison researchers have developed a low-cost, gallium arsenide-based laser device that exhibits high performance operation in the 1.55-micron region, up to elevated temperatures. The laser’s active region is deposited on a substrate of GaAs and includes electron quantum well layers of GaAsN or InGaAsN, and a hole layer quantum well of GaAsSb with a type II alignment. The composition of these quantum well layers can be selected to provide light emission at wavelengths ranging from 1.3 to 3.0 microns.

Vertical-Cavity, Surface-Emitting Semiconductor Laser Arrays

UW-Madison researchers have developed a method of coupling arrays of VSELs that overcomes the problems of prior technologies and provides a stable, diffraction limited output at high power levels. The array contains at least four core elements arranged in a 2-D rectangular array. The core elements are separated and surrounded by a matrix region to provide an array of antiguided phase-locked VCSELs.

Frequency-Narrowed High-Power Diode Laser System with External Cavity

UW–Madison researchers have developed a high-power diode laser array system that uses an external cavity to narrow the spectral width, changing the output power from a broad spectrum to a very narrow spectrum. The light from each emitter is collimated, reflected off a diffraction grating and imaged back onto the emitter. This causes each diode to preferentially lase at the wavelength that is fed back. The result is a diode laser array that uses a much greater portion of the laser's output power.

Frequency-Narrowed High-Power Diode Laser Array Method and System

UW–Madison researchers have developed a high-power diode laser array system that uses an external cavity to narrow the spectral width, changing the output power from a broad spectrum to a very narrow spectrum. The light from each emitter is collimated, reflected off a diffraction grating and imaged back onto the emitter. This causes each diode to preferentially lase at the wavelength that is fed back. The result is a diode laser array that uses a much greater portion of the laser's output power.

Vertical-Cavity Surface-Emitting Lasers with Anti-Resonant Reflecting Optical Waveguides

UW–Madison researchers have developed a VCSEL that uses an anti-resonant reflecting optical waveguide (ARROW) to reduce the edge radiation losses for the fundamental mode. This structure is capable of providing single-mode output at higher powers than conventional VCSEL devices.

Single Mode Surface-Emitting Semiconductor Laser

UW–Madison researchers have developed a high power surface-emitting semiconductor laser that operates in a single mode with a single lobe far-field radiation profile. The device comprises a semiconductor substrate and an epitaxial structure on the substrate that includes a layer with an active region at which light emission occurs. A distributed feedback grating is incorporated with the epitaxial structure and comprises periodically alternating grating elements to provide optical feedback.

Aluminum-Free Semiconductor Laser for High Power Output

UW–Madison researchers have developed a semiconductor laser that utilizes an aluminum-free active region layer to emit light in the wavelength range of about 700-800 nm. By utilizing an aluminum-free active layer in conjunction with the performance enhancement of high band-gap confinement and cladding layers, many improvements over conventional high power lasers are seen.

The semiconductor laser comprises an epitaxial structure that is grown on a GaAs or AlGaAs substrate and includes an aluminum-free active region layer and cladding layers adjacent to the confinement layers. The active region layer comprises at least one compressively strained InGaAsP quantum well surrounded by transitional layers. High band-gap InGaAsP cladding and confinement layers may be utilized to suppress carrier leakage.

Semiconductor Light-Emitting Source for Increased Power Levels

UW–Madison researchers have developed a semiconductor light-emitting source that incorporates antiguided lateral confinement of emitted light and an asymmetric transverse optical waveguiding structure. The semiconductor structure includes a substrate, an active region, optical confinement and cladding layers on opposite sides of the active region and at least one core element at which light emission occurs. Means for providing optical feedback are incorporated in the structure when it is operated as a laser; facets at the longitudinal edges of the structure are formed to be sufficiently antireflective when the semiconductor source operates as an amplifier.

High Power Distributed Feedback Semiconductor Laser

UW–Madison researchers have developed a high power edge-emitting semiconductor laser that encompasses a distributed feedback grating that is formed in an aluminum-free section. The laser includes a semiconductor substrate such as GaAs and an epitaxial structure on the substrate including a layer with an active region where light emission occurs. The distributed feedback grating provides optical feedback for a selected effective wavelength of light generation and acts upon the light generated in the active region to produce lasing action and emission of light from an edge face of the semiconductor laser.

Intersubband Quantum Box Semiconductor Laser

UW–Madison researchers have developed an intersubband quantum box laser which utilizes suppression of phonon-assisted energy relaxation processes to provide an efficient, practical quantum cascade laser. The semiconductor laser comprises multiple layers of semiconductor material and an active structure in which light emission occurs. The active structure has a two-dimensional array of quantum boxes, which suppress phonon-assisted transitions.