HERACLES
The HERACLES facility, currently under construction at the Townes Laser Institute, will feature outstanding output parameters. With expected output pulses of duration ~8 fs, energy up to 2 mJ at repetition rates as high as 25 kHz and carrier envelope phase (CEP) stabilization of the oscillator and amplifier chain, the HICEPS meets the requirements of the most demanding experiments. This facility enables the generation of peak powers approaching 0.25 TW at high repetition rates in a compact tabletop design and makes it an ideal source for driving the generation of high harmonics (HHG) and opens the pathway to the emerging field of attoscience.
High Intensity Femtosecond Laser (HIFL)
The High Intensity Femtosecond Laser (HIFL) is a commercial Chirped-Pulse Amplifier (CPA) system with flexible output in repetition rate (10 Hz or 1 kHz) with energy up to respectively 20 mJ and 2 mJ. The Ti:Sapphire oscillator (OSC: Tsunami – Spectra Physics) is pumped by a Nd:YLF doubled CW laser (PUMP1: Millenia – Spectra Physics) generates sub-35 femtosecond pulses with a spectrum centered at 800 nm. It is capable of generating an 80 MHz pulse train of transform limited pulses, ~5 nJ in energy and <35 fs in duration.
The output is directed through an Acousto-Optic Programmable Dispersive Filter pulse shaper (DAZ: Dazzler – Faslite) which is typically used to correct for pulse narrowing in the last pass of the laser amplifier, but may be used for arbitrary pulse shape and temporal profile generation. This shaped pulse is then expanded in grating stretcher (STR) about 10,000 times its initial pulse duration for safe and efficient amplification in a regenerative amplifier.
This stretched beam is then directed into a regenerative amplifier (REG) pumped by a diode-pumped, kHz repetition rate, Q-switched, intra-cavity doubled, Nd:YLF laser (PUMP3: Evolution 30 – Spectra-Physics), where it is amplified in ~12 passes to an energy of ~3 mJ. This amplified pulse can then be directed into a grating compressor (COMP) for an output of ~2.4 mJ and 30 fs at 1 kHz or may be directed into a 2-pass power amplifier (DP) pump by a 600 mJ Nd:YAG laser (PUMP2: Quanta-Ray Pro 290 – Spectra-Physics) for further amplification to >30 mJ prior to pulse compression. The 10 Hz output is typically 30 mJ and 30 fs. Pulse temporal parameters are measured with a Grenouille from Swamp Optics. Pulse spatial profile is measured using a Spiricon 980 camera and associated hardware/software.
2um Laser Propagation Facility
One of the most attractive properties of thulium as a fiber laser dopant, relative to more established ytterbium and erbium hosts, is the extremely wide wavelength range of laser output from ~1.8 ? 2.1 ?m. This ?eye safe? wavelength range is interesting for a variety of reasons and potential applications.
For example:
- There are several regions of very low atmospheric absorption within the wavelength range of Tm:fiber, well-suited for long-range propagation for applications such as LIDAR or directed energy.
- Vibrationally resonant absorptions from trace water vapor and CO2 occur within the emission band of Tm:fiber, making this a useful band for trace gas analysis.
- The wide laser tunability range is sufficient to enable the amplification of 100 fs pulses to high peak powers using all-fiber architecture.
For all of these cases, it is necessary to characterize the propagation of Tm:fiber emission. Towards this goal, we have conducted 1 km laser range experiments using a tunable Tm:fiber MOPA system producing >200 W output power with narrow linewidth (<200 pm) from ~1.94 ? 2.1 ?m at the Innovative Science & Technology Facility (ISTEF) in Merritt Island Florida. By tuning the laser wavelength, we measured the relative transmission over the 1-km range and compared it with MODTRAN simulation. These measurements confirm that there atmospheric transmission windows from 2.03 ? 2.05 ?m and for wavelengths >2.07 ?m.
We have also conducted short range transmission measurements using broadband Tm:fiber sources for illumination and our Yokogawa AQ6375 Optical Spectrum Analyizer for data collection. This provides us with a diagnostic with <50 pm spectral resolution and high dynamic range. This diagnostic is capable of detecting CO2 absorption features after ~2 m propagation in air, despite the low ~0.04% percentage of atmospheric CO2.
IMRA Partnership (Laser-Schedule)
The FCPA µJewel consists of a Yb-fiber oscillator / amplifier system for producing microjoule level energy, 1 µm wavelength output. The system uses chirped pulse amplification (CPA) in a large-core Yb-fiber amplifier. The unique fiber-amplified architecture allows 1-3W average power and turnkey operation with no water cooling.
- Single-box, fixed repetition rate or flexible platform, variable repetition rate solutions available
- Repetition rates from 100 kHz to 5 MHz
The IMRA µJewel system is provided to us directly from IMRA America, Inc. under a special PAL agreement. This agreement allows third parties to access the laser facility within the Laser Processing Technology Team. For further information please contact mramme@creol.ucf.edu.
The laser system enables us to generate femtosecond pulses with a variable repetition rate from 100 kHz stepwise up to 5 MHz. The external compressor allows for pulse durations as short as 350 fs. The system provides pulse energies up to ~3 µJ depending on the repetition rate. The fiber design makes the laser extreme robust and reliable.
In our current setup the laser output can be guided to an autocorrelation system for adjustment of the pulse duration or to a 3D-microprocessing station. The station provides a computer-controlled 3D positioning stage, online imaging of the sample to irradiate, stepless control of pulse energy and beam polarization as well as the capability to focus the beam using various microscope objectives.
Khz Femtosecond Laser Materials Processing Facility
The kHz femtosecond laser materials processing facility enables fundamental and applied research in a variety of different fields, including integrated optics, advanced materials science, photochemistry, life sciences, and manufacturing. The ultrafast transfer of energy from laser pulses to the material ensures higher spatial (sub-micrometer) and temporal (sub-picosecond) selectivity of the materials processing, as well as a significantly reduced heat input compared to longer laser pulses. The low repetition rate reduces cumulative heating between pulses, making this facility ideal for the research on heat-sensitive applications such as ablative processing and light-matter interaction with biological specimens. The high intensities that can be generated with femtosecond laser pulses enable the exploration of the non-linear absorption mechanisms utilized for the processing of dielectric materials. The ability to utilize single femtosecond pulses allows an implementation of pump-probe experiments for time-resolved studies of various laser-matter interaction phenomena.
In addition to the fundamental wavelength at 800 nm and its second harmonics at 400 nm, the facility is equipped with a femtosecond optical parametric amplifier (fs-OPA) that extends the output wavelength range into the near- and mid-IR. The ability to tune the frequency of the ultrafast laser light can be utilized for laser processing of wide band gap materials and spectroscopic studies.
The primary utilization of the facility within the Laser & Plasma Laboratory at the Townes Laser Institute covers the fabrication of 3D volumetric optical and microfluidic structures in transparent materials, high-precision machining of different classes of materials, and time-resolved studies of laser-matter interaction in different materials.
Fiber Processing
In order to support thulium fiber laser development efforts, the Laser Plasma Laboratory (LPL) utilized a DURIP from ARO to purchase several pieces of equipment critical for processing large diameter fibers for use in laser systems. This includes a cleaver capable of placing an angled facet on fibers from 125 μm to 1.5 mm in diameter (Vytran LDC-200); a glass-processing platform with the ability to splice (including polarization alignment), taper and fuse large diameter fibers (Vytran GPX-3400); and a fiber recoater for splice protection (Vytran PTR-200).
The facility provides us with the ability to fabricate high-power fiber systems and components in house. This allows us to produce integrated systems for applications requiring compactness and a minimum of free-space optical components, and provides us flexibility in fabricating and optimizing fiber laser systems.
Thermal Lensing Characterization Facility
Thermally induced distortion is a primary limiting factor on average power scaling in laser systems, as even passive components suffer from laser induced heating at sufficiently high average powers. The laser induced thermal distribution will be a convolution of the laser beam distribution, the substrate absorption at the laser wavelength, and the thermal conductivity of the substrate. Thus, particularly for lasers with Gaussian-like beam profiles, a ?thermal lens? will form in which the focal length is proportionate the amount of laser heating.
One pervasive issue, associated with our research and development of thulium fiber lasers, is the significant optical absorption of OH in the 2 um wavelength regime. Relative to high power ytterbium fiber lasers at 1 um, this means more absorption due to OH contamination is the fiber itself, beam delivery optics such as lens and mirrors, and even water vapor in the air. While the thermal lensing does not cause beam distortion within the fiber, due to the dominance of the waveguide, it is significant for beam delivery optics.
To characterize the significance of such effects in a variety of materials subject to high power 2 um light, we have constructed the Thermal Lens Characterization Facility. It utilizes a homemade Tm:fiber laser oscillator, producing up to 60 W average power with M2 < 1.2, with a 4 mm collimated beam diameter on the sample. The thermally induced wavefront distortion of an off-axis probe beam is measured using an Imagine Optic HASO 3 FIRST Shack-Hartmann wavefront sensor. Our measurements demonstrate >1? wavefront distortion in BK7 for an irradiance of ~1.5 kW/cm2, and ~4X larger wavefront distortion in BK7 than fused silica due to larger optical absorption and larger thermal expansion coefficient.