This PDF file contains the front matter associated with SPIE Proceedings Volume 11980, including the Title Page, Copyright information, and Table of Contents.

We report on sub-100-fs pulse generation from a passively mode-locked laser based on a novel disordered crystal, lanthanum calcium lithium niobium gallium garnet (LCLNGG) codoped with thulium (Tm³⁺) and holmium (Ho³⁺) ions. In the continuous-wave regime, the Tm,Ho:LCLNGG laser generated a maximum output power of 350 mW at 2080.5 nm with a slope efficiency of 23.8%. By using a Lyot filter, the laser wavelength was continuously tuned over a broad range of ~210 nm (1904.1 – 2114.1 nm). Soliton mode-locking was initiated and stabilized by a transmission-type single-walled carbon nanotube saturable absorber. Pulses as short as 63 fs were obtained at a central wavelength of 2072.7 nm with an average output power of 63 mW at a pulse repetition rate of ~102.5 MHz.

A comparative study of three disordered calcium niobium gallium garnet (CNGG)-type crystals codoped with Tm³⁺ and Ho³⁺ ions is performed: (i) without host modifiers (CNGG), (ii) with Li⁺ cations added (CLNGG), and (iii) with Li⁺ and La³⁺ cations added (LCLNGG), all grown by the Czochralski method. The crystals exhibit inhomogeneously broadened luminescence bands extending beyond 2.1 μm. A diode-pumped Tm,Ho:LCLNGG laser generates 562 mW at 2082 nm with a slope efficiency of 17.4% and a laser threshold of 0.46 W. A continuous wavelength tuning between 1904.1 and 2121.1 nm (tuning range: 217 nm) is achieved with this new garnet compound. The Tm,Ho:LCLNGG crystal is promising for generation of ultrashort pulses from mode-locked lasers emitting above 2 μm.

Mid-IR laser systems are now widely used in a variety of applications. Cr2+:CdSe and Cr2+:ZnSe crystals are considered among the most promising active media due to the wide tuning range in the mid-IR range. However, they have a high thermooptic coefficient and lower thermal conductivity. These properties lead to strong thermal effects and limitations in power scaling. One solution is to use a MOPA configuration. A sophisticated mathematical model was developed to select the optimal parameters, taking into account the temperature variation in the crystal, the beam geometry, the luminescence lifetime dependence on temperature, the refractive index gradient, and its effect on the intensity profile. In this paper, we present a comparison of theoretical data and experimental values according to the developed model. The comparison demonstrated the validity of the simulation results and the ability to use the model to calculate the optimal MOPA system configuration.

We present the first demonstration of a multi-joule diode-pumped Tm:YLF amplifier. The compact demonstrator setup, consisting of a Tm:YLF-based oscillator producing ~20mJ, 20ns pulses at 1880nm wavelength that seeds a diode pumped four-pass Tm:YLF power amplifier, generated pulse energies up to 3.9J with a maximum net gain exceeding 200. No saturation effects were observed within this amplifier, as the output pulse energies increased exponentially with the input pump power. When the amplifier was seeded with the free-running oscillator, with pulse durations still significantly shorter than the 15ms radiative lifetime of Tm:YLF, energies of up to 38J were achieved. To the best of our knowledge, this represents over a 100-fold improvement in the highest reported pulse energy from a Tm:YLF amplifier, and nearly an order of magnitude higher energy than any laser operating near 2μm. These results show that Tm:YLF, when operated in an efficient high repetition rate extraction regime and combined with a high-capacity heat removal technique, has the potential to enable a new class of efficient, high peak and average power laser systems to meet the demands of next generation scientific and industrial applications.

High peak power, 355 nm ultraviolet (UV) short-pulse lasers are very useful for many applications, such as, materials processing and 3D printing. However, such applications are limited by the size and cost of UV lasers. We report the design and fabrication of a < 6 MW peak power, very compact and cost-effective 355 nm UV microlaser. We used a specially designed Nd:YAG/ Cr4+:YAG microchip laser pumped through a fiber combiner. The in-house fabricated fiber combiner enabled a compact design using several low-cost/low-power, air-cooled laser diodes to pump the microchip laser, without sacrificing pump beam quality needed for end-pumping. The microchip laser used a [100]-cut Nd:YAG with an undoped YAG end-cap as the gain medium. This enabled high output power without depolarization, which is essential for high efficiency wavelength conversion. A low initial transmission Cr4+:YAG was used as the passive Q-switch to obtain high peak power. We achieved 11.3 mJ pulse energy, 935 ps pulse width, <12 MW peak power with good beam quality at 1064 nm, without using a MOPA system. Third harmonic generation was performed by sum-frequency generation using Type I and Type II LBO crystals. We achieved 4.1 mJ pulse energy, 645 ps pulse width, resulting in 6.36 MW peak power at 355 nm. The conversion efficiency from 1064 nm to 355 nm was 52%. These are the highest pulse energy and peak powers achieved at 355 nm using a compact microchip laser. Our low-loss fiber combiner design for pumping is scalable, to further increase the output power.

We demonstrate a Nd:YLiF₄ laser emitting at the 1053nm transition while side-pumped at 797nm by a VBG equipped diode. Initially, a plane-concave cavity is employed using a total internal reflection at the crystal pump face. The laser operated in QCW-mode and produced 68% of slope and 66% of optical efficiency with 67 W of peak output power, while having a multimode beam quality. These efficiencies are the highest ever reported for the Nd:YLF₄ pumped at 800nm.

We demonstrated a monolithic nonplanar ring oscillator (NPRO) with a piezo-electric tuning range of 3.5 GHz with 192 volts applied, corresponding to a tuning coefficient of 18.2 MHz/volt. Useful bandwidth was limited by a resonance at 338 kHz and an anti-resonance at 420 kHz. This performance was achieved by making the NPRO small, with a small distance between the piezo-electric transducer and the laser beam, and by using a piezo-electric material with favorable properties. This large frequency modulation range and wide frequency modulation bandwidth, combined with unsurpassed coherence and high power, make this an attractive laser for frequency-modulated continuous-wave (FMCW) LIDAR. The tested laser provides over 500 mW at 1064 nm. Comparable performance will be possible at the eye-safe Nd:YAG wavelength of 1319 nm.

This paper presents an intra-cavity beam-shaping technique using digital holograms in a continuous-wave (CW) diode-pumped Nd: YAG laser module. It shows that with the aid of digital holograms, the intensity distribution of the laser output can be modified to various optical beam shapes such as Laguerre-Gaussian (LGp;l) and Hermite-Gaussian (HGm;n). We used digital holograms that were encoded with amplitude masks that matched the desired laser output beam shape, LGp;l and HGm;n modes of different orders p, l and m, n, respectively. The research demonstrated the possibility of using digital lasers to simulate optical elements to pursue advanced laser material processing.

In this work, the spectroscopy and laser characterization of Er,Pr-doped GGAG crystal was carried out in the temperature range from 80 K to 300 K. The tested Er,Pr:GGAG (13.4 at. % of Er³⁺ and 0.09 at. % of Pr³⁺, thickness 3.3 mm) crystal in form of disc had plan-parallel polished faces without anti-reflection coatings. During measurements, the Er,Pr:GGAG was attached to temperature controlled copper holder and it was placed in a cryostat vacuum chamber. The Er,Pr:GGAG was pumped by a fibre-coupled laser diode radiation (pulse duration 1 ms, repetition rate 20 Hz, wavelength 962 nm). The transmission and fluorescence spectra together with the fluorescence decay times at the upper (⁴I_11/2) and lower (⁴I_13/2) laser level were measured in the temperature range from 80 K to 300 K. The fluorescence decay time of manifold ⁴I_11/2 (upper laser level) is slightly increasing with rising temperature from 325 μs (80 K) to 341 μs (160 K) and then its decreasing to 295 μs (300 K). On the other hand, the intensity of up-conversion radiation was increasing with decreasing temperature. During the laser experiments a hemispherical resonator (150 mm in length) with flat pumping mirror (HT < 94 % and HR < 99 % @ 960 - 980 nm) and spherical output coupler (r = 150 mm, R = 97.5 % @ 2.65 - 2.95 μm) was used. The tunability of emitted laser wavelength at 80 and 300 K was tested using MgF₂ birefringent plate, and several laser lines at 2874 nm, 2832 nm, 2805 nm, 2718 nm, and 2702 nm were obtained. In the pulsed laser regime, the highest slope efficiency 16 % (with respect to absorbed power) and maximum output power 118 mW were reached at 5 % duty cycle. The laser radiation generated by Er,Pr:GGAG laser (wavelength 2.9 μm) is close to the absorption peak of water (3 μm) and it can be tuned in a wide spectral range which could be advantageous for various applications in medicine or spectroscopy.

We present the influence of optically inactive Gd³⁺ ions codoping on the spectroscopic and laser properties of a novel fluoride Tm,Gd:SrF₂ crystal. Eight crystals in shape of single-fiber (r = 2 mm, l = 5 mm) with different low Gd³⁺ (0, 0.5, 1, 2 at.%) and Tm³⁺ (2 and 3 at. %) concentrations were tested. The addition of an inactive ion Gd³⁺ had an influence on the absorption spectra, especially on the value of the absorption coefficient in the 0.76 μm pumping band. The fluorescence spectra excited at 763 nm have been influenced only slightly promoting lower wavelength peaks of ³F₄→3H₆ transition. The 2 μm fluorescence decay time was measured. The decay curves exhibited double exponential behavior, and two components of lifetime were estimated. While the faster component of about 5.5 ms increased with the Gd³⁺ addition, the slower component of about 19.7 ms was not affected. The Tm,Gd:SrF₂ quasi-cw laser was tested. The pumping diode emitting at a wavelength of 763 nm was operating in the pulse regime (5 ms pulse duration, 10 Hz repetition rate). A 148 mm long hemispherical resonator formed by a flat pump mirror and a curved (r = 150 mm) output coupler was used. The Gd3+ addition had not a strong effect on the laser performance and the high slope efficiency up to 57 % with maximum output power amplitude up to 5.5 W at 1949 nm was achieved with all samples. For wavelength tuning, a MgF₂ birefringent filter was used and the wide tunability range of up to 199 nm (1807 – 2006 nm) was reached.

Delivery of flashlamp pumped Er:YAG laser radiation (λ = 2.94 μm) by a hollow waveguide is quite well known. The goal of this study was to investigate the potential of connection of a novel diode pumped Er:YAG laser with a hollow glass waveguide and to design a new possibility for mid-IR radiation transfer. The expected use would be in medicine and therefore a sufficiently flexible and lossless delivery system is required. The base of transfer system was a special cyclic olefin polymer-coated silver (COP/Ag) hollow glass waveguide. The length of the waveguide was 2.15 m and inner diameter 700 μm. Transmission as a function of the input laser power and spatial distributions of the output beams were investigated depending on bending angle of waveguide. The transmission in the straight configuration were 89 % and decreased to 79 % when the fiber was bent to an angle of 180° with a bending radius of 15 cm. The output beam spatial structure was not changed for investigated bending angles 0°, 45°, 90°, and 180° (bending radius of 15 cm). These transmission values predetermine the use of the special hollow glass waveguides in conjunction with the novel diode pumped Er:YAG laser for further research with subsequent use in medicine.

Ho-doped yttrium aluminum perovskite Ho:YAP (Ho:YAlO3) is a promising material for the construction of high-power lasers, operating in 2.1 µm spectral region. We present the dependencies of key spectroscopic properties on Ho-doping concentration and on Ho:YAP crystal orientation. Three Ho:YAP crystals with various Ho-doping concentrations were grown by Czochralski method: 0.26 at.% Ho/Y, 0.45 at.% Ho/Y, 1.05 at.% Ho/Y. The uncoated samples were prepared in the form of polished wafers 2.8 mm thick with diameter up to 45 mm and in the form of an oriented cuboid (6 x 7 x 8mm). The detailed polarization resolved absorption spectra were measured with a high resolution in the range from 300 up to 6500 nm. The polarization resolved emission spectra were investigated in the range from 500 up to 3500 nm. The ⁵I₇ upper-laser-level lifetime was measured using a confocal method. From the obtained data, the absorption cross-sections in all investigated spectral ranges were determined and the Judd-Ofelt analysis was performed. It was found that the Ho-doping concentration significantly influenced mainly the upper ⁵I₇ laser level lifetime, which drops from 5.8 ms for the lowest doping to 4.7 ms for the highest tested Ho-doping. Using the oriented Ho:YAP cuboid (1.05 at.% Ho/Y), laser emission reaching the quantum limit under Tm-fibre excitation (1939 nm) was reached. By an appropriate choice of the Ho:YAP crystal orientation and reflectance of the laser output coupler, it was possible to achieve laser action at wavelengths of 2083, 2102, 2118, and 2130 nm, or to generate laser radiation at several wavelengths simultaneously.

We have demonstrated a pulse-on-demand operation in the mid-infrared region using a Cr:ZnSe laser pumped with a Qswitched Tm:YAG laser. The pulse-on-demand operation was accomplished by controlling the pump pulse train. In the burst pulse mode operation, we could control the number of pulses, the pulse interval, and each pulse height in a packet. In addition, the wavelength of the Cr:ZnSe laser can be tuned in the region of 2.3–2.6 μm. The total pulse energy of a single packet was a maximum of 0.2 mJ at 2.5 μm.

Composite Tm3+-doped Tm:Y3Al5O12, (Tm:YAG) microchip lasers were investigated. Effect of bonding the microchip rod with undoped YAG cap at one (YAG/Tm:YAG) and two (YAG/Tm:YAG/YAG) ends was studied and the results were compared to an unbonded Tm:YAG sample. The experiments were performed under 785 nm and 1700 nm diode pumping. The microchip rods had 3 mm diameter and 5/9/13 mm length. Faces were planar, polished and coated for HT at 1685 nm and 785 nm and HR at 1900–2050 nm at pumping end. Output coupler reflectivity value was R=98 The composite microchip lasers had advantageously high beam quality. At the maximum pumping power, the M2 parameter, measured by the knife-edge method, was M2=5.8 for the non-composite sample, which reduced to M2=4.5 for single-bonded and to M2=2.2 for double-bonded sample. There was a 30 End caps did not significantly influence output power or efficiency. The best obtained slope efficiency with respect to the absorbed power was 54.

Diode-pumped efficient continuous-wave Yb:LLF (Yb:LiLuF4) laser was demonstrated with output power in the multiwatt range. The laser operated in the fundamental mode and produced up to 7.7 W of output power. The laser showed record high 64% of optical-to-optical efficiency and up to 73% slope efficiency with respect to the absorbed pump power. Laser wavelength tuning range was found to be >40 nm around the central wavelength of 1053 nm.

We have demonstrated a diode-pumped Yb:CALGO laser operating at 13.85 MHz repetition rate with high pulse energy and high peak power. The laser delivered 750 mW of output power at 21 W of incident pump power. The shortest pulses obtained were 73 fs using a 15% output coupler. The corresponding pulse energy was 54 nJ and the peak power was 744 kW. A White cell configuration was used to extend the laser cavity. To the best of our knowledge, this is the first ever femtosecond laser operated with a White cell configuration.

A high-power compact continuous-wave (CW) Nd:YAG laser with greatly improved beam quality operating at 946 nm is reported. A simple concave-plane cavity was made with a composite Nd:YAG laser crystal which was pumped by a fiber-coupled laser diode. A maximum output power of 9.63 W was obtained at an incident pump power of 31 W with beam quality factor M2 ~ 5. To the best of our knowledge, this is the highest output power at 946 nm with such a beam quality that was produced from diode-pumped Nd:YAG lasers using bulk crystals.

We report what we believe is the first demonstration of a continuous-wave Nd:YAP laser under in-band diode pumping around 910 nm. The laser produced the maximum average output power of 1.15 W at 1079 nm. The maximum output power was limited by the available absorbed pump power and not the thermal effects. The presented results are preliminary and further work is in progress to improve the performance of the laser system.

We demonstrated continuous-wave dual-wavelength operation of a Yb:YAP laser with intracavity birefringent element. The laser produced a wide range of wavelength pairs with spectral separation from 1 nm up to 35 nm. The average output power reached up to 800 mW. Dual-wavelength radiation was generated owing to the broad gain bandwidth of the Yb:YAP crystal and custom design of a birefringent filter.

We report on the Czochralski growth, polarized optical spectroscopy, thermal lensing and diode-pumped laser operation of a Yb³⁺-doped monoclinic “mixed” calcium rare-earth oxoborate crystal, Gd_0.235Y_0.672Yb_0.093Ca₄O(BO₃)₃ (Yb:GdYCOB). The absorption, stimulated-emission and gain cross-section spectra are determined for light polarizations E || X, Y, Z. The maximum σSE above the zero-phonon line is 0.61 x 10^-20 cm² at 1022.4 nm (for E || X) and the luminescence lifetime of Yb³⁺ ions is 2.37 ms. The gain spectra of Yb:GdYCOB extend beyond 1.15 μm. The thermal lens is studied for the three principal cuts, X-cut, Y-cut and Z-cut, and it is found to be positive. A continuous-wave diode-pumped X-cut Yb:GdYCOB laser generates 9.27 W at ~1050 nm with a slope efficiency of 68.2%, linear laser polarization E || X and nearly diffraction-limited beam (M² _x,y < 1.16). A continuous wavelength tuning from 1020.9 to 1086.3 nm (a tuning range of ~65 nm) is achieved for the Z-cut crystal and the laser polarization E || X.

We report on the continuous-wave (CW) and Kerr-lens mode-locked (KLM) operation of an ytterbium (Yb³⁺) doped orthorhombic calcium rare-earth borate Yb:Ca₃Gd₂(BO₃)₄ (Yb:GdCB) disordered crystal. A high quality 10 at.% Yb:GdCB crystal was grown by the Czochralski method. An X-shaped astigmatically compensated linear cavity was employed for evaluating the CW and KLM laser performance of an a-cut (sp. gr. Pnma) Yb:GdCB crystal. Pumping with a single-transverse mode, fiber-coupled diode laser at 976 nm, a maximum CW output power of 548 mW was obtained at 1049 nm with a slope efficiency of 67.8% and a linear laser polarization (E || b). A broad wavelength tuning range of ~88 nm (1001 – 1089 nm) was achieved in the CW regime. Stable KLM operation was initiated and stabilized by a semiconductor saturable absorber mirror (SESAM). Nearly Fourier-transform-limited pulses as short as 33 fs were generated at a central wavelength of 1055.3 nm with an average output power of 98 mW for a pulse repetition rate of ~67.3 MHz.

Raman spectroscopy has allowed for the acquisition of Raman signatures for pheromone components, or chemicals, which are found in the pheromones of crop key pests: (Z, Z)-11,13-Hexadecadienal, (Z, Z, Z, Z, Z) and (3,6,9,12,15)- Tricosapentene for Naval Orange Worm, NOW, moth affecting tree nuts, and (E, Z)-7,9-Docedadien-1-yl Acetate (European Grapevine, EVG, moth). Raman signatures were successfully extracted, and peaks were assigned to different vibration and rotational modes for each primary chemical. Notably, the signatures of these primary chemicals are very unique, which not only confirms the ability of Raman to detect these chemicals, but to also differentiate between them. The sensitivity of the system’s ability to detect these chemicals at very low concentrations was evaluated. Starting with 100% pure concentrated chemicals, series of dilutions were performed, testing various concentrations down to 0.1%, in both ethanol and acetone. Similar trends and peaks were observed, but with different intensities, the solvent being the only difference. Characterization of singular signatures standalone and in mixtures is conducted using Principal Component Analysis (PCA) as a way to ease separation. Principal component analysis is a multivariate data analysis technique, which allows for the better understanding of numerous factors which affect the spectral variation across different samples. A new set of axes, or principal components, are aligned with the maximum directions of variance inside of a data set. Scores, loadings, and residuals become the new matrices which are created through his method of analysis. By using the principal component analysis technique complex Raman spectra were successfully interpreted by revealing compounds and differences between each sample.

Narrowband Single-Longitudinal-Mode (SLM) lasers are important in a number of applications, including frequency metrology, LIDAR, nonlinear optics, holography, and in optical fiber communications. In recent years, the need for such devices has been embraced by the US Navy, who seek low amplitude and phase-noise devices to enhance low noise-figure RF photonic capabilities for avionic and electronic warfare (EW) applications.

The cryogenically cooled Cr²⁺,Fe²⁺:Zn_1-xMg_xSe (x ≈ 0.4) single crystal with the thickness of ~3.6 mm was investigated under two different excitation wavelengths of the Q-switched Er:YAG laser (λ ≈ 2.94 μm, Eout ≈ 50 mJ) and by the gain-switched Fe:ZnSe laser (λ ≈ 4.05 μm, Eout ≈ 9 mJ). Because of relatively low Fe2+ ions concentration, the absorption coefficients at 78 K and 300 K ranged between 3 cm-1 and 2 cm-1 for both excitation wavelengths used. Absorption and fluorescence spectra, fluorescence lifetime as well as laser output characteristics were measured at low temperatures (78–180 K). The Cr,Fe:Zn_1-xMg_xSe (x ≈ 0.4) laser system was able to generate laser radiation at ~5 μm at liquid nitrogen (LN₂) temperature of 78 K under both ~2.94 μm and ~4.05 μm laser excitation. The laser oscillation wavelength was shifted up to ~5 μm compared with a typical Fe:ZnSe output (~4.0–4.1 μm at LN₂ temperature) due to the high amount of magnesium in the host material. Moreover, the oscillation wavelength was shifted even farther by increasing temperature of the active medium. The laser output energy was ~1.34 mJ and ~0.14 mJ for the ~2.94 μm and ~4.05 μm laser excitation, respectively. The beam profile structure was approximately fundamental for both excitation wavelengths used. The results present a novel mid-infrared 4.7–5.1 μm coherent laser source based on cubic A^IIB^VI matrix using direct excitation at wavelengths of ~2.94 μm or ~4.05 μm.

We report on the fabrication and characterization of single clad Adhesive-Free Bonded (AFB®) ZnSe/Cr²⁺:ZnSe/ZnSe and double clad composite AFB® ZnS/ZnSe/ Cr²⁺:ZnSe/ZnSe/ZnS architectures of core thicknesses between about 0.04 mm to 0.2 mm with a gradient refractive index due to diffusion of Cr²⁺ into undoped ZnSe. Waveguide structures and bulk composites exhibit improved transmission to 473 nm and refined and partially oriented grain morphology. We derive the transport characteristics of Cr⁺² dopant ions within the bulk as function of major process variables according to the measured optical transmission spectra at the AFB® Cr:ZnSe/ZnSe interfaces.