In recent years, ceramic sesquioxide materials have emerged as a promising alternative to crystalline laser hosts for near- and mid-infrared laser applications. Ceramics offer a number of manufacturing advantages over crystals including lower fabrication temperatures and the amenability to forming much larger size samples. In this work, a number of RE ions, doped into multiple sesquioxide hosts, are spectroscopically characterized in order to assess their potential for near- and mid-infrared laser applications. Characterization methods included absorption and fluorescence spectroscopy as well as decay dynamics, all measured as functions of temperature. The results are analyzed in order to determine the best laser gain media in the near- and mid-infrared spectral regions.

A large number of rare-earth (RE) activated materials have been investigated to develop new solid state infrared (IR) laser sources for potential applications in atmospheric sensing, material processing, laser remote sensing, medicine, and free space communications. RE3+-doped low-phonon chalcogenide glasses have shown efficient mid-IR emission as well as lasing at room temperature. In this work, we report the results of a comparative study of mid-IR spectroscopic properties of RE3+ doped chalcogenide glasses (e.g. GaGeX (X= S, Se)) aimed at exploring their potential for efficient mid-IR laser operation.

The development of mid-IR lasers faces some unique challenges when striving to achieve the highest efficiency and power output. Most critical among these challenges is luminescence quenching of the relatively closely-spaced upper and lower laser levels, usually occurring through the process of multi-phonon relaxation. This quenching can be mitigated by using gain materials with small maximum phonon energies. In this work, mid-IR spectroscopic characterization of RE3+ doped cesium cadmium chloride (CsCdCl3) crystals was performed. The transition probabilities of RE3+ ions using Judd-Ofelt analysis as well as the multiphonon non-radiative transition rates in RE3+:CsCdCl3 were estimated. Obtained experimental results, inclusive of temperature dependent absorption and fluorescence studies, transition cross-sections, and fluorescence dynamics, were interpreted from the standpoint of optimization for diode-pumped ~3-5 um laser development.

We report an approach to generation of optical frequency combs in the spectral range 2 – 20 µm. The 2-cycle, multi-Watt laser at the repetition rate 80 MHz is based on a polycrystalline Cr:ZnS. The bandwidth of the super-octave ultrafast Cr:ZnS laser source at the central wavelength 2.4 µm is extended to the long-wave IR range (5 – 20 µm) via optical rectification in non-oxide nonlinear materials: GaSe, ZGP. The key advantages of Cr:ZnS frequency comb technology is high efficiency of optical-to-optical conversion from low-cost cw EDFL light to fs MIR pulses, and ultra-low timing jitter. These advantages, in turn, has allowed us to implement shoe-box-sized, light-weight, frequency combs that open new avenues in imaging, sensing, and spectroscopy. Our preliminary evaluations confirm the applicability of the developed sources for dual-comb spectroscopy.

Laser directed energy effectors combine the beams from several singlemode optical fiber amplifiers into a single beam with near diffraction-limited divergence. Coherent beam combination achieves this by tiling an aperture with individual beams and co-phasing these beams. Deployment on mobile platforms requires a rugged effector with low size, weight and power consumption. These constraints challenge beam combiner architectures based on discrete optics as power is scaled via channel count. We describe how monolithic arrays of freeform optics solve these problems by providing collimation, beamshaping and high fill-factor aperture tiling for large numbers of fiber channels in a rugged low-SWaP configuration.

Broad area diode lasers operate with high power and efficiency but suffer from poor beam quality. Diffraction-limited lasers with equivalent power offer a disruptive alternative for applications ranging from fiber laser pumping to automotive LIDAR. We report >9 W continuous output power with 50% EO from tapered diode lasers at 885 and 980 nm, and >3 W power with 25% EO at 1550 nm. We show for the first time that beam quality degradation with increasing injection is completely mitigated and maintain a slow-axis M^2 of 1.3 from threshold to rollover. These devices achieve an order-of-magnitude increase in brightness over commercially available high power diode lasers.

This video was recorded at the 2022 SPIE Defense + Commercial Sensing conference.

Advancements in high-power delivery of narrow linewidth single mode fiber lasers have garnered significant amount of recent interest with the advancement of hollow-core fibers. It has been shown that by propagating high intensity light through an air core as opposed to a solid glass core one can significantly delay the onset of nonlinear effects deleterious to laser performance. Precisely designed anti-resonant hollow-core fibers have been shown to handle both 100s of watts of average power and low-loss propagation while simultaneously resisting bending losses and discouraging the propagation of any higher order modes. This paper presents the recent progress in surpassing more the 1 kW of single mode 1070nm optical power through one such fiber at a length of more than 10m coiled on a 30cm mandrel.

Rare-earth-doped fibers with single-crystal cores have the potential for 10x higher TMI threshold than their glass counterparts and are a promising candidate for use as gain media in high-power laser systems. Their utility has been limited by parasitic optical losses and difficulty in fabrication. This paper explores methods to reduce the losses in these fibers in the core, in the cladding and at the core-cladding interface. Fabrication methods are also discussed.

We present comprehensive numerical models of the cladding pumped Raman laser and cladding pumped amplifier inclusive of random distributed feedback due to Rayleigh scattering. Useful analytical approximations to the numerical models of laser and amplifier shall be presented and compared to experiment.

We report the laser operation of spinning mirror-based mechanically Q-switched (MQS) 2940 nm Er:YAG with record 805 mJ output energy in a single 61 ns pulse and ~10 ns pulse jitter. The laser was operated at 1Hz repetition rate and 670 Hz rotational rate of the spinning mirror. The highest output energy was achieved with the use of a 300 mm long MQS Er:YAG laser cavity consisting of 70% output coupler, 7x120 mm AR coated Er(50%):YAG crystal, and spinning HR mirror. The maximum output energy was limited by the optical damage of the Er:YAG AR coatings.

Laser filaments generated by ultrashort pulse (USP) lasers achieve diffractionless propagation for distances surpassing the Rayleigh distance, making them highly beneficial to long-range outdoor applications. However, filaments generated by a single USP are limited to a clamped electron density, intensity, and lifetime. Here, we demonstrate how spatial and temporal engineering can overcome these limitations and enhance a variety of filament applications. We also prove the robustness of structured filaments in propagation studies on a turbulent, kilometer scale range. A strong understanding of beam engineering and generating structured filaments has the potential to improve many applications.

Filaments, formed by ultrashort pulsed laser (USPLs) with high peak powers, deliver high intensities and a plasma channel to km-scale distance, without the need for focusing elements. These properties make them viable for long-range outdoor applications, including propagation to or at high altitudes where air pressure is a fraction of that at sea level. Since filament formation and characteristics are known to vary with air pressure, here, we analyze how critical filamentation thresholds and properties change as pressure decreases, through experiment and simulation. This study indicates that filament applications are indeed feasible over long distances to or at high altitudes.

The majority of filamentation studies have focused on near infrared (NIR) filaments, which have been demonstrated to propagate over many times the Rayleigh range with clamped intensity, electron plasma density, and beam diameter. Long wavelength infrared (LWIR) laser light sources, however, have not been extensively studied for filamentation. Here, we discuss filamentation in both wavelength regimes and introduce a new ultrafast CO2 system capable of producing high-power 10 µm picosecond pulses. Future work is outlined which will significantly increase the output power of the CO2 laser for upcoming studies and allow direct comparison of NIR and LWIR filaments.

Laser filaments generate intensities at remote distances that exceed the plasma and ablation thresholds of solid materials, but intensity clamping limits the impact of a single pulse. To overcome this fundamental restraint, we have engineered a high-energy solid-state Titanium:Sapphire laser to generate nanosecond-duration bursts of ultrashort pulses. This temporal structuring of the laser energy enhances nonlinear propagation and several interaction mechanisms with solid targets including ablation, acoustic shockwave production, and remote RF generation. This presentation will discuss the impact of the pulse parameters and burst format on these effects in both low and high-altitude environments through experiments and simulations.

Recently, the technique of infrared/terahertz Double Resonance Spectroscopy (DRS) was proposed for remote sensing of trace gases in atmospheric conditions. The atmospheric window of transmission is in the 9-11 µm range, which makes CO2 lasers highly suited for this application. DRS is a valuable detection method because of increased measurement specificity due to terahertz ro-vibrational signature detection. Preliminary DRS measurements utilizing a pulsed CO2 laser source with a known trace gas in a vacuum chamber are discussed. A plan is then presented for future DRS experiments at ambient pressure using ultrafast laser techniques.

We review the status of commercially available USP (ultra short pulse) laser amplifiers and their key components, analyzing how technology innovation and industrial/scientific applications are pushing boundaries in performance and reliability. These improvements will be instrumental in facilitating adoption in challenging environments like defense applications. We provide examples of performance requirements for various applications and describe the challenges to overcome to increase performance and reliability of fielded USP lasers and amplifiers.

The performance of advanced laser systems for defense and aerospace applications rely heavily on the capabilities of the system building blocks. Due to the sensitive nature of the end applications, such components also often require domestic US sources to ensure supply chain security and facilitate engagement in the product development cycle. Coherent maintains a full range of domestic critical component manufacturing capabilities to support the defense and aerospace laser industry, including optical fiber, semiconductor diode lasers, crystals, optical isolators, coatings and freeform optics, all from US-based manufacturing locations. Coherent has also expanded the internal manufacturing capabilities, enabling the manufacture of complete laser component assemblies and subsystems, allowing contract partners to leverage our internal laser manufacturing expertise. We will review our latest component capabilities and discuss how these components map to critical defense applications.

A new design is developed for a non-mechanical, tunable Pancharatnam phase based optical beam steering device that drastically improves the steering resolution for large angles (up to 11°). A fringe field switching structure is used to construct a Pancharatnam phase, an in-plane spiral pattern with a given pitch length, in a liquid crystal cell. The pitch length of a Pancharatnam phase device is the length along the aperture corresponding to a phase increase of one wave. A design utilizing neighboring pitch lengths of different sizes achieves a steering angle corresponding to the average length of the neighboring pitches. The alternating pitch length design is advantageous to the resolution of the device because the length of a single pitch is restricted to an integer number of electrodes in the fringe field switching structure. By implementing the new alternating pitch design, the pitch length can change by a smaller non-integer number of electrodes resulting in finer steering.