Research Terms
Researchers at the University of Central Florida have developed a tunable laser with broadband coherent output spectrum within the mid-infrared (IR) range using a chirped quasi-phase-matched optical parametric amplifier/difference frequency generator (CQPM OPA/DFG)-based design.
Technical Details
This novel system involves a non-mechanical method of changing the relative timing of a pump pulse versus the seed pulse. The temporal variation varies the spatial/temporal overlap location of the spectrally narrow pump pulse over the spectrally broad seed spectrum taking place within the CQPM nonlinear medium. The overlap position regulates the phase-matched, seed pulse portion as the signal in the OPA or the seed for DFG.
Piezo-electric fiber stretchers are used to vary the relative pulse timing, thus enabling the output tuning from the OPA or DFG without using any moving parts. Fiber-coupled optical amplitude and/or phase modulators can also be included in either the pump or signal channels to provide control over the optical duty cycles as well as provide fine pulse control.
Researchers at the University of Central Florida have invented a low loss optical nanocomposite material made of glass and high concentrations of nanocrystals (NCs). Unlike conventional crystal laser media, the new glass ceramic medium can be drawn into fiber, coated onto films, deposited as waveguides or formed as bulk optical elements. The new material has better index-matched and viscosity-tuned attributes than other doped glass/NC-containing materials, enabling high NC loading levels. Though similar materials may exhibit luminescence or random lasing in bulk form, they fail to maintain optical function like the new nanocomposite can when formed into a fiber or planar film. Well-suited for laser sources operating in wavelengths of 2 µm or greater, the material can be used for applications such as molecular spectroscopy, non-invasive medical diagnostics and atmospheric sensing.
The invention comprises an optical nanocomposite material and a process for producing said material, which is made of glass and active NCs (rare earth or transition metals). The material creates a matrix which is index-, dispersion-, and thermo-optically matched, enabling the creation of a glass ceramic with unique optical properties. By further tuning the viscosity of the composite, it can be drawn into fiber form, dissolved into a solution and deposited as a thin film, or used as a bulk optical component.
One example use of the invention blends nanosized crystalline powders (NCs) with multicomponent chalcogenide glass (ChG) to form an optical nanocomposite of glass/NCs with matching optical properties (index, dispersion, dn/dT). Specialized methods ensure homogeneous physical dispersion of NCs within the glass matrix during preparation, while minimizing agglomeration and any mismatch in the coefficient of thermal expansion.
The University of Central Florida invention is a multi-stage diamond Raman Master Oscillator Power Amplifier (MOPA). Raman lasers, in general, do not require rare-earth doping, as the vibrational modes of the atomic structure or crystal lattice are the media for the effect. It is a nonlinear effect, and as such, the gain is proportional to the intensity of the 1st Stokes signal and the pump. Diamond Raman lasers have proven to be very valuable, as the large Raman shift allows access to otherwise difficult wavelength regions while using well-developed lasers as pumps. Also, as the thermal conductivity of diamond is the highest of any bulk material, such lasers are very resistant to thermal lensing. Normally, the caveat of Raman lasers is the limited gain achievable in 1st Stokes before 2nd Stokes is generated; the onset of 2nd Stokes saturates the pump depletion. This means a specific design for a Raman laser works typically only across a relatively narrow range of input intensities (that is, high threshold and low maximum scalability).
The University of Central Florida invention is a novel laser that generates directed energy at a distance consisting of a narrowband tunable radio-frequency (RF) emission in the MHz and GHz ranges for military and commercial applications. This is accomplished by creating a localized transient micro-laser plasma source with a periodic pulse function. The system is additionally constructed of coaxially stacked laser pulses with known time separations, which through the Fourier transform generate a tunable narrowband RF tone and associated harmonics at target.
The University of Central Florida invention is a mechanism for the use of temporally resolved custom pulse shapes as well as co-pumping with multiple wavelengths to control the breadth and flatness of a supercontinuum source. High brightness white light sources enable otherwise impossible sensing and detection applications; however, high average power sources have so far been limited to laboratory settings, as most rely on either photonic crystal fibers, ultrashort pulses, or feedback mechanisms that prohibit power scaling. With new applications (including military) requiring very high average power (greater than 200 watts), new architectures are required. Additionally, most laboratory demonstrations are limited in that they are inflexible once designed. The UCF technology offers unprecedented control over spectral breadth and flatness in real-time.
The mechanism for this control allows for core pumping of single-mode fiber, core pumping of graded-index fiber, or cladding pumping; as such, the nonlinear fiber can be step-index core pumped, step-index cladding-pumped, or graded-index. Regardless, no rare-earth doping is required. High germanium content is beneficial to accelerate the nonlinear process but not critical to the design of the system. This application is scalable to the many hundreds of watts level at least, as the heat load is small and spread across a long (greater than 15 meters) fiber.
Partnering Opportunity
The research team is looking for partners to develop the technology further for commercialization.
Researchers at the University of Central Florida have developed a unique laser system with stable, self-starting mode-locked lasers. The compact lasers use lower optical elements to produce ultra-short light pulses with sufficient energy for micro and nano-machining applications.
Extremely short duration optical pulses, which are known as femtosecond pulses, are ultra-short pulses that make it possible to investigate ultrafast processes, and can be used for fast optical data transmission. Ultra-short pulses have unique advantages in that extremely high energies can be created over ultra-short timescales. These high energies allow access to unique physical processes that only occur at these energies. Mode-locked lasers are lasers that can be made to produce pulses of light of extremely short duration (femtoseconds). These lasers are crucial for high-speed signal processing, communications, micro and nano-machining, imaging, and sensing applications.
Current conventional, commercial, ultrafast mode-locked lasers have basic constituents, which include an active laser medium, resonator mirror, and optical components, usually prisms that compensate for dispersion in the resonator. However, such systems are complex, costly, unstable, and require high pump power levels.
Technical Details
With the UCF invention, the femtosecond regime of the ultra-short light pulses minimizes heat deposition and allows the fabrication of fine features (<10 microns). This novel, compact and commercially viable femtosecond pulse technology enables a wider range of ultrafast laser applications, making it more available to both the research and the development communities.
Researchers at the University of Central Florida have developed a new fiber laser design that index-anti-guides by gain-guiding laser light through the core of a fiber that may be up to 500 micrometers in core size. The laser then delivers a single mode, high power laser light through a variety of off axis optical pumping into fiber cladding.
The fabrication of optical fiber that includes optically amplifying materials has resulted in the development of fiber lasers. These novel laser systems boast high power potential, thermal and vibration stability, compact size and a very high quality (often diffraction limited) output beam. Also, because the light is already contained in an optical fiber, these lasers make it very easy to deliver light where desired. The advancements of fiber lasers have pushed researchers toward new types of fiber that will optimize the size, power, and stability of the output beam, and researchers at UCF have applied a very unique light guiding phenomenon to produce a very attractive new fiber laser.
Technical Details
By employing a process called gain-guiding, light may be guided in regions of a fiber where traditionally, under zero amplification, it would be forbidden to propagate, a process called index-anti-guiding. Shown herein, a fiber with a doped, low index core is used to guide laser light while a higher index cladding region around the core is used to guide laser pump light. The new fiber laser design offers very large spot size operation in the fundamental mode which enables safer high-power operation under easy optical pumping conditions.
The University of Central Florida invention is a thulium fiber geometry design specifically geared for in-band pumping. Thulium-doped fiber lasers have gained much interest recently in the field of directed energy because of the potential to create eye-safe sources at 2 µm. This design will take advantage of the higher efficiencies and lower thermal load of in-band pumping. The triple cladding design offers the best balance between thermal effects, modulation instability threshold and pump absorption. This geometry has the potential to provide greater than 5 kilowatts (kW) of continuous wave (CW) output power across the 1950-2100 nanometer (nm) region. Thulium-doped fiber lasers have gained much interest recently in the field of directed energy.