The development of new solid-state laser materials for mid-infrared (mid-IR) laser sources continues to be interest for potential applications in remote sensing of bio-chemical agents, IR countermeasures, and IR spectroscopy. Fluorescent materials based on Ho3+ doped crystals and glasses with narrow phonon spectra cover a wide wavelength range between ~1-4 µm. In this work, spectroscopic characterization on infrared emission properties of trivalent holmium (Ho3+) doped potassium lanthanum chloride (K2LaCl5) were explored. K2LaCl5 is slightly hygroscopic but possesses a maximum phonon energy of 235 cm-1. The low maximum phonon energy of K2LaCl5 leads to low non-radiative decay rates and efficient IR fluorescence. The studied Ho3+ doped K2LaCl5 material was grown by Bridgman technique. Using ~900 nm excitation, IR emissions centered at ~1.66, ~1.995, and ~3.90 µm were observed from Ho:K2LaCl5 corresponding to the 5I5-->5I7, 5I7-->5I8, and 5I5-->5I6 transitions of Ho3+ ions. Spectroscopic results and data modeling including the Stark level energies, Judd-Ofelt analysis, transitions cross-sections, and fluorescence dynamics will be presented at the conference.
In the pursuit of efficient mid-Infrared laser host materials, we developed a dual-phase nanocomposite composed of a majority species (MgO) which provides high thermal conductivity and a rare earth doped minority species (Er:Y2O3) featuring a low maximum-phonon energy. This material was prepared using a co-precipitation method where both components are synthesized together for intimate mixing on the smallest scale. Preparation parameters were tuned to achieve a small crystallite size in order to limit scattering at the grain boundaries between the two different species. Optical characterization of the prepared materials included percent transmission (%T) as well as Raman measurements and Er fluorescence spectroscopy. Once suitable transmissivity was achieved, %T results were compared to Mie scattering calculations to gauge the average grain size in the material; and we determined the smallest average Y2O3 grain sizes achieved in our materials so far was 80 nm in diameter.
Pr3+ has three excited manifolds with the right energy spacings for emission between 3.5 and 5.5 microns, and can be excited efficiently using laser diodes developed for telecommunications. In the potential laser crystal Pr:RbPb2Cl5, we have observed strikingly strong fluorescence in this wavelength range following 1.53-micron excitation. Careful analysis indicates this must be due to two cross-relaxation processes that, together, efficiently convert one Pr3+ initially excited to the 3F3 manifold into three ions excited to the 3H5 manifold. This newly discovered “three-for-one” crossrelaxation process in Pr3+ may greatly enhance its utility as a mid-infrared laser ion.
A nanoparticle (NP) doping technique was used for making erbium-doped fibers (EDFs) for high energy lasers. The nanoparticles were doped into the silica soot of preforms, which were drawn into fibers. The Er luminescence lifetimes of the NP-doped cores are longer than those of corresponding solution-doped silica, and substantially less Al is incorporated into the NP-doped cores. Optical-to-optical slope efficiencies of greater than 71% have been measured. Initial investigations of stimulated Brillouin scattering (SBS) have indicated that SBS suppression is achieved by NP doping, where we observed a low intrinsic Brillouin gain coefficient, of ~1× 10-11 m/W and the Brillouin bandwidth was increased by 2.5x compared to fused silica.
We have investigated stimulated Raman scattering in the 4H polytype of SiC, due to its excellent thermal conductivity which is of great importance for power scaling of Raman lasers. Spectroscopy verifies the sample’s polytype and precludes any significant admixture of other polytypes. Tests indicate the moderate optical quality of this commercially available sample. Using pump-probe measurements around 1030 nm, we find the Raman gain coefficient of the major peak at 777 cm-1 to be 0.46 cm/GW. Although this value is only modest, calculations and experience with other Raman materials indicate that Raman lasing of 4H SiC should be possible with reasonable intensities of 1064-nm pulsed pumping.
Nanoparticle (NP) doping is a new technique for making erbium-doped fibers (EDFs); the Er ions are surrounded by a
cage of aluminum and oxygen ions, substantially reducing Er3+ ion-ion energy exchange and its deleterious effects on
laser performance. Er-Al-doped NPs have been synthesized and doped in-situ into the silica soot of the preform core. We
report the first known measurements of NP-doped EDFs in a resonantly-core pumped master oscillator-power amplifier
(MOPA) configuration; the optical-to-optical slope efficiency was 80.4%, which we believe is a record for this type of
Due to the favorable thermal properties of sesquioxides as hosts for rare earth laser ions, we have recently studied the
spectroscopy of Er:Lu2O3 in the 1400-1700 nm wavelength range, and here report its comparison with our earlier results
on Er:Y2O3 and Er:Sc2O3. These studies include absorption and fluorescence spectra, fluorescence lifetimes, and
inference of absorption and stimulated emission cross sections, all as a function of temperature. At room temperature,
optical absorption limits practical laser operation to wavelengths longer than about 1620 nm. In that spectral range, the
strongest stimulated emission peak is that at 1665 nm in Er:Sc2O3, with an effective cross section considerably larger
than those of Er:Y2O3 and Er:Lu2O3. At 77K, the absorption is weak enough for efficient laser operation at considerably
shorter wavelengths, where there are peaks with much larger stimulated emission cross sections. The three hosts all have
peaks near 1575-1580 nm with comparably strong cross sections. As we have reported earlier, it is possible to lase even
shorter wavelengths efficiently at this temperature, in particular the line at 1558 nm in Er:Sc2O3. Our new spectroscopic
studies of Er:Lu2O3 indicate that its corresponding peak, like that of Er:Sc2O3, has a less favorable ratio of stimulated emission to absorption cross sections. Reasons for the differences will be discussed. We conclude that for most operating scenarios, Er:Sc2O3 is the most promising of the Er-doped sesquioxides studied for laser operation around 1.5-1.6 microns.
The spectroscopic properties of Ho3+-doped YVO4 were studied at cryogenic and room temperatures in the 2 μm spectral region to clarify recent observations of efficient dual-wavelength laser operation in this material. Polarized absorption cross sections were measured, and stimulated emission cross sections were determined using the reciprocity method coupled with Füchtbauer-Ladenburg calculations. The observed laser emission wavelengths were at 2041.7 nm, 2054.2 nm, and 2068.5 nm; the first two corresponding to pi transitions and the third to a sigma transition. Gain cross section calculations were used to predict which of the three wavelengths would lase for a given output coupler reflectivity. In depth analysis of the gain cross section in the region between 80 K and 100 K showed that the laser output wavelength is very susceptible to minor changes in temperature.
We present spectroscopic properties and lasing results of Ho3+-doped Yttria (Y2O3), LuAG
(Lu3Al5O12), and YAG (Y3Al5O12) at wavelengths beyond 1.6 μm. High resolution
measurements of absorption and stimulated emission cross sections of Ho3+ in these hosts from
77K to 300K are reported. Laser operation based on 5I7 to
5I8 transitions of Ho3+ in these hosts is
Remote monitoring of carbon dioxide (CO2) is becoming increasingly
important for homeland security needs as well as for studying the CO2
distribution in the atmosphere as it pertains to global warming problems.
So, efficient solid-state lasers emitting in the 1.55 - 1.65 μm spectral
range, where CO2 absorption lines are, (i), plentiful and, (ii), carry
significant relevant information, are in great demand. Reported here is the
first laser performance of resonantly pumped Er3+-doped scandia (Sc2O3)
ceramic. The laser was operated in the cryogenically-cooled regime with
the quantum defect (QD) of only 4.5%, which, along with superior thermal
conductivity of scandia, offers significant eye-safe power scaling potential
with nearly diffraction limited beam quality. Slope efficiency of 77% and
Q-CW output power of 2.35 W were obtained at 1605.5 nm which has
significant utility for counter-IED applications.
Efficient ultra-low-photon-defect resonantly diode-pumped Er:YAG cryogenically-cooled laser is demonstrated for
the first time. Quasi-CW diode pumping by InGaAsP/InP 10-diode bar stack (without spectral narrowing) was
implemented. Laser performance at ~80°K in this first experiment was found to be 71.5% efficient (output power
versus power absorbed in the cavity mode, slope). Er:YAG laser output variations with the gain medium
temperature was investigated. Maximum quasi-CW power of ~65 W was achieved by optimization the gain
medium operating temperature. and to photon number
splitting attacks, thus resulting in a high efficiency in terms of distilled secret bits per qubit. After having successfully tested the feasibility of the system , we are currently developing a fully integrated and automated prototype within the SECOQC project . We present the latest results using the prototype. We also discuss the issue of the photon detection, which still remains the bottleneck for QKD.
Recently there has been increasing interest in high quality ceramic laser gain materials, particularly for high-energy lasers, due to the successful application of high-volume advanced ceramics consolidation techniques to transparent oxide gain materials. In this paper, a brief comparison of manufacturing techniques is presented, including an overview of the co-precipitation process and the solid-state reaction process. Merits and risks of each will be presented from a processing viewpoint. Ceramic Nd:YAG in particular shows promise for high power laser design. The program reported here is also compiling a definitive database to compare ceramic and single crystal Nd:YAG materials. Uniform doping levels of up to 9 at% Nd3+ have been reported by Konoshima Chemical Co. in ceramic Nd:YAG, and studied by the US Army Research Laboratory and the US Air Force Research Laboratory. All ceramic Nd:YAG materials studied to date have exhibited similar, if not identical, spectroscopic parameters to those measured for single crystal samples. Thermal properties, laser damage thresholds and refractive indices for a range of temperatures and wavelengths are reported. Diode-pumped free running laser experiment results with highly concentrated (up to 8 at% Nd3+) ceramics and their comparison with our modeling results are presented. High pulse repetition frequency actively (AO) Q-switched laser experiments are in progress. While there are still challenges in the manufacturing of ceramic laser gain materials, and the benefits of the application of ceramic technology to laser material are yet to be fully realized, ceramic Nd:YAG shows promise and could provide new options to the laser design engineer.
Lasers have come a long way since the first demonstration by Maiman of a ruby crystal laser in 1960. Lasers are used as scientific tools as well as for a wide variety of applications for both commercial industry and the military. Today lasers come in all types, shapes and sizes depending on their application. The solid-state laser has some distinct advantages in that it can be rugged, compact, and self contained, making it reliable over long periods of time. With the advent of diode laser pumping a ten times increase in overall laser efficiency has been realized. This significant event, and others, is changing the way solid-state lasers are applied and allows new possibilities. One of those new areas of exploration is the high energy laser. Solid-state lasers for welding are already developed and yield energies in the 0.5 to 6 kilojoule range. These lasers are at the forefront of what is possible in terms of high energy solid-state lasers. It is possible to achieve energies of greater than 100 kJ. These sorts of energies would allow applications, in addition to welding, such as directed energy weapons, extremely remote sensing, power transfer, propulsion, biological and chemical agent neutralization and unexploded and mine neutralization. This article will review these new advances in solid-state lasers and the different paths toward achieving a high energy laser. The advantages and challenges of each approach will be highlighted.