High Lasing Efficiencies Research Articles

Highly efficient Ho: YAP laser with 202 W of linearly polarized output power at 2118 nm

We report on high power and efficient operation of a compact Ho: YAP laser in-band pumped at 1931 and 1943 nm with a high-power and narrow-linewidth Tm-doped fiber laser. Using a 0.5at. % Ho3+ doped Ho: YAP cut along the b-axis and a simple two-mirror resonator, up to 202 W of output power has been generated at ∼2118 nm for 336 W of absorbed pump power at 1931 nm, corresponding to a slope efficiency of 61.2% with respect to the absorbed pump power. The laser output is linearly polarized along the c-axis with a polarization extinction ratio (PER) of ∼20.0 dB. Results presented in this work verify the superior power scaling capability of Ho: YAP at ∼2.1 μm with high lasing efficiency.

Methods for adjusting feedback in terahertz lasers

The optimal feedback coefficient in an active open resonator is an important condition for high lasing efficiency. For precise selection of the optimum communication and maintaining the optimum in all modes of laser operation, the ability to adjust smoothly the communication is required. Terahertz (THz) lasers have a number of features that one should take into account when choosing feedback control schemes. The paper presents a review and comparative analysis of the schemes of laser resonators (THz) in the range with a smoothly controlled radiation output. The authors consider both long known and widely used, as well as the latest schemes of laser resonators. Smooth adjustment can be realized in resonators formed by metal mirrors of total internal reflection and output mirrors in the form of metal mirrors with holes or one-dimensional metal gratings. The analysis of the advantages and disadvantages of each of the considered optical schemes of laser resonators is carried out.
 It is shown that the given resonator schemes make it possible to control and optimize the feedback in the laser during its operation. All of them are not very complex and can be realized by re-equipping existing lasers. The choice of a specific scheme should be made in accordance with the specifics of the laser application. The use of resonators with smooth coupling control makes it possible to achieve high efficiency of lasers at all energy operating modes.

Towards Efficient and Photostable Red‐Emitting Photonic Materials Based on Symmetric All‐BODIPY‐Triads, ‐Pentads, and ‐Hexads

The development of efficient and stable red and near-IR emitting materials under hard radiation doses and/or prolonged times is a sought-after task due to their widespread applications in optoelectronics and biophotonics. To this aim, novel symmetric all-BODIPY-triads, -pentads, and -hexads have been designed and synthesized as light-harvesting arrays. These photonic materials are spectrally active in the 655-730 nm region and display high molar absorption across UV-visible region. Furthermore, they provide, to the best of our knowledge, the highest lasing efficiency (up to 68 %) and the highest photostability (tolerance >1300 GJ mol-1 ) in the near-IR spectral region ever recorded under drastic pumping conditions. Additionally, the modular synthetic strategy to access the cassettes allows the systematic study of their photonic behavior related to structural factors. Collectively, the outstanding behavior of these multichromophoric photonic materials provides the keystone for engineering multifunctional systems to expedite the next generation of effective red optical materials.

Lasing of pyrromethene 567 in solid matrices

Lasing characteristics of pyrromethene PM567 are investigated both theoretically and experimentally. It is established that the operating lifetime of solid-state active media based on PM567 in polymeric PMMA matrix can be significantly increased by proper purification of initial substances. It is demonstrated that addition of 8-MMAPOSS leads to an increase in the lasing efficiency; however, the operating lifetime in this case can decrease. Also, it is demonstrated using the XMCQDPT2 method that one of the main reasons for high lasing efficiency is the absence of S1→Sn and T1→Tn reabsorption at the lasing wavelength.

Change of Boron Substitution Improves the Lasing Performance of Bodipy Dyes: A Mechanistic Rationalisation

Bodipy laser dyes are highly efficient but degrade rapidly in solution by reacting with in situ generated singlet oxygen ((1)O(2)). To increase the lasing lifetimes of these dyes, we have designed and synthesised two different congeners of the widely studied Pyrromethene 567 (PM567) by substitution at the boron centre and/or at both the boron centre and the meso position. The two new dyes showed high lasing efficiencies with increased photostability. The results of theoretical and pulse radiolysis studies revealed that the substitution at the boron centre reduced the (1)O(2) generation capacity of these dyes as well as their rate of reaction with (1)O(2), thereby enhancing their lifetimes even under lasing conditions.

New 8‐Amino‐BODIPY Derivatives: Surpassing Laser Dyes at Blue‐Edge Wavelengths

The development of highly efficient and stable blue-emitting dyes to overcome some of the most important shortcomings of available chromophores is of great technological importance for modern optical, analytical, electronic, and biological applications. Here, we report the design, synthesis and characterization of new tailor-made BODIPY dyes with efficient absorption and emission in the blue spectral region. The major challenge is the effective management of the electron-donor strength of the substitution pattern, in order to modulate the emission of these novel dyes over a wide spectral range (430-500 nm). A direct relationship between the electron-donor character of the substituent and the extension of the spectral hypsochromic shift is seen through the energy increase of the LUMO state. However, when the electron-donor character of the substituent is high enough, an intramolecular charge-transfer process appears to decrease the fluorescence ability of these dyes, especially in polar media. Some of the reported novel BODIPY dyes provide very high fluorescence quantum yields, close to unity, and large Stokes shifts, leading to highly efficient tunable dye lasers in the blue part of the spectrum; this so far remains an unexploited region with BODIPYs. In fact, under demanding transversal pumping conditions, the new dyes lase with unexpectedly high lasing efficiencies of up to 63 %, and also show high photostabilities, outperforming the laser action of other dyes considered as benchmarks in the same spectral region. Considering the easy synthetic protocol and the wide variety of possible substituents, we are confident that this strategy could be successfully extended for the development of efficient blue-edge emitting materials and devices, impelling biophotonic and optoelectronic applications.

Sulforhodamine B doped polymeric matrices: A high efficient and stable solid-state laser

We report the first systematic study on the laser action of Sulforhodamine B (SRB). Rhodamine B (RB), with similar molecular skeleton but with different phenyl substituents, was analysed to define the structural keystones in influencing their optical properties. Synthesis and laser characterization of photosensitized homopolymer, linear and crosslinked copolymers, and silicon-modified organic matrices were carried out. High lasing efficiencies, of up to 57%, were obtained with high photostability since the laser output remained stable, with no sign of photodegradation after 100,000 pump pulses at 10 Hz in the same position of the sample. These are, to the best of our knowledge, the topmost results achieved with new red-photosensitized materials to apply in advanced optical devices in this spectral region.

Recent Advances in Microwave, Millimeter-Wave and Plasma-Assisted Processing of Materials

We present results on microwave, millimeter-wave, and millimeter-wave-driven plasma-assisted processing of materials. The research is primarily based on two systems- a 2.45 GHz, 6 kW S-band system and an 83 GHz, 15 kW gyrotron-based quasi-optical system. The S-Band system is used to synthesize nanophase metals, metal mixtures, and metal oxides by our patented continuous microwave polyol process, which has potential for large scale and low cost production. This system is also being investigated to develop techniques for titanium melting and sintering. The 83-GHz system is used for rapid sintering of ceramic powder compacts to produce polycrystalline materials with limited grain growth. An important application is to the development of polycrystalline laser host materials for high power solid-state lasers, where the requirement is for transparency with high optical quality and good lasing efficiency. We are currently investigating solid-state reactive sintering of Nd-doped YAG (Yttrium Aluminum Garnet) from commercial oxide powders. This has thus far yielded translucent samples with good fluorescence lifetime of the lasing state. Techniques for further reducing light scattering by residual pores are being investigated. Finally, the millimeter-wave system is being used in the development of millimeter-wave plasma-assisted diamond deposition, as the quasi-optical system has significant advantages over conventional microwave plasma-assisted diamond deposition systems. The results and implications of this wide range of materials processing experiments are presented and discussed.

Recent Advances in Microwave and Millimeter-Wave Processing of Materials

We are using 2.45 GHz (S-Band) microwave systems and an 83-GHz, gytrotron-based, millimeter-wave beam system in material processing and other areas. We use one 2.45 GHz system in preparation of nanophase metals, metal mixtures and metal oxides, via the patented continuous microwave polyol process, with potential for large scale, low cost production. Of interest are precious metals, mixtures of magnetic and nonmagnetic metals, and mixed metal oxides for ceramic precursors. The other S-Band systems are used to develop repair techniques for ceramic matrix composites where the repairs are heated to 200-1000°C. A portable, battery-powered system is being developed for field repairs, and promises to be much more practical than alternative approaches (e.g., heating blankets). The 83-GHz system is being used in rapid sintering of polycrystalline ceramic materials intended for use in high power solid state lasers, where the requirement if for sintering to transparency with high optical quality and good lasing efficiency. Transparent Yb-doped yttria has been produced with hybrid conventional/millimeter-wave sintering of nanophase powders, as well as theoretically dense YAG. Another application for the millimeterwave beam system is in consolidation and bonding of hard coatings to light alloys, such as SiC on titanium, where the beam system allows heating of the coating to very high temperatures without overheating the metallic substrate. Finally, the millimeter-wave system is being used in the development of millimeter-wave plasma-assisted diamond deposition, where the quasi-optical system has significant advantages over conventional microwave plasma-assisted diamond deposition. Results for these various areas will be presented and discussed.

Glycidyl methacrylate as a new host material for laser dyes

AbstractThis article reports on the laser action of pyrromethene 597 and pyrromethene 567 doped in the novel solid polymeric matrix glycidyl methacrylate. Mirrorless lasing was observed when samples with diameters of 10 mm and lengths of 20 mm, with different dyes concentrations, were transversely pumped at 532 nm. The influence of the dye concentration on the laser measurements included the peak wavelengths, output energies, conversion efficiencies, and laser gains. Relatively high lasing efficiencies (up to ∼ 60%) were obtained from these new polymeric materials with very good photostability, where a decrease of only 65% in the initial laser output energy was observed after pumping by 60,000 shots of 15 mJ at 10 Hz. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 59–63, 2007

Spectral, luminescent, and lasing properties of 3-(benzothiazolyl-2)-7-hydroxy-and-8-hydroxycoumarins

The spectral and luminescent properties of 3-(benzothiazolyl-2)-7-hydroxy-and-8-hydroxycoumarins and their protolytic forms are studied experimentally and with the help of quantum-chemical calculations using the method of intermediate neglect of differential overlap with spectroscopic parameterization. The photophysical processes in these compounds are analyzed. The fluorescence of 3-(benzothiazolyl-2)-8-hydroxycoumarin is shown to be extremely weak due to intercombination conversion of the excitation energy. The introduction of a proton-accepting substituent next to the hydroxy group of the molecule (at position 8) leads to intramolecular proton transfer, resulting in formation of a zwitterion, with the probability of the proton transfer increasing in the excited S1 state. The lasing ability of the protolytic forms of the molecules under excitation with a XeCl excimer laser is studied. It is shown that the compounds have the highest lasing efficiency in the anionic form.

High lasing oscillation efficiency of Eu(III) complexes having remarkably sharp emission band

Luminescent Eu(III) complexes with bis-phosphine oxide ligands were synthesized. Geometric structures of novel Eu(III) complexes were determined by single-crystal X-ray diffraction. One of the Eu(III) complexes showed remarkably sharp red emission and large stimulated emission cross-section (full width at half maximum (FWHM) = 2.1 nm, stimulated emission cross-section = 1.80 × 10 −20 cm 2). The sharpness of the emission bands of the Eu(III) complexes was discussed in terms of the symmetry of the geometrical structure.

Efficient oscillation regimes of an HF laser pumped by a nonchain chemical reaction initiated by a self-sustained discharge

The amplitude — time and spectral characteristics of laser radiation and discharge characteristics in mixtures of SF6 with hydrogen and hydrocarbons at a high lasing efficiency are investigated. Lasing efficiencies of ~10 % with respect to the deposited energy are obtained under the pumping from capacitive and inductive energy storage units. It is shown that, during a pump pulse, the maximum efficiencies are achieved at high values of the parameter E/p in the laser gap. When profiled electrodes and UV preionisation are used, a specific output energy of a nonchain HF laser of ~140 J L-1 atm-1 and a lasing efficiency of ~4.5 % with respect to the stored energy were obtained. It is shown that the emission spectrum of a nonchain HF laser operating at high lasing efficiencies becomes significantly wider and cascade lasing is realised on the ν(3–2) → ν(2–1) → ν(1–0) vibrational transitions at several rotational lines.

Efficient and stable dye laser action from modified dipyrromethene BF2 complexes

We report on the lasing action of modified dipyrromethene BF2 complexes in air-equilibrated liquid solutions. All recent dyes share a common chromophore core and were dissolved in apolar, polar nonprotic, and polar protic solvents. When pumped transversely at 534 nm, nearly solvent-independent laser emission was obtained with efficiencies well over 40% in most cases. Highest lasing efficiency was 59%. Under continuous ultraviolet irradiation some of these dyes demonstrated improved photostability as compared with commercial dye pyrromethene 567.

Influence of universal intermolecular interactions on lasing of oxazine 17

An investigation was made of the influence of universal intermolecular interactions of the characteristics of lasing of oxazine 17 solutions. The highest lasing efficiency was observed for solutions in polar aprotic solvents in which intermolecular relaxation of orientational nature ensured the most favorable (for lasing) relative positions of the energy levels of the dye molecules: this reduced the lasing threshold, compared with that in nonpolar solvents. The maxima of laser emission (stimulated radiation) and fluorescence were practically coincident for polar solvents; in the case of nonpolar solvents, the former were displaced toward longer wavelengths relative to the latter.

Efficiency of lasers utilizing vapors of complex organic compounds subjected to hard ultraviolet (266 nm) pumping

Measurements were made of the efficiency of stimulated emission in the range 329–400 and 500 nm by a series of complex organic compounds in gaseous mixtures with pentane (1.5×1021cm−3) when the vapor was excited by the fourth harmonic of neodymium laser radiation (266 nm, 5 nsec, 20 mJ). Lasing of PPD (340 nm) and PBD (352 nm) vapors was observed for the first time. The highest lasing efficiency was obtained for vapors of 1,4-di-(benzoxazole-2'-yl)benzene (20%), PBD (13%), and PPF (3%). Lasing was found possible in the case of coumarin 6 and 7-diethylamino-3(2'-benzoxazolyl)-coumarin vapors mixed with ether (1.5×1021cm−3) and subjected to hard ultraviolet (266) nm pumping. A study was made of the dynamics of the pump absorption, lasing, and fluorescence. Low-threshold transverse stimulated scattering of the pump radiation was observed for the first time for active media based on complex organic molecules. The fluorescence lifetime was estimated for gaseous mixtures under working conditions. An analysis was made of the characteristics of the chemical structure of those compounds which exhibited a high lasing efficiency as vapors.

Efficient energy transfer dye lasers in spectral region of near ultraviolet to violet

AbstractAn experiment was performed on the operation and development of energy transfer dye lasers (ETDL), using scintillator dye mixture to obtain higher efficiency and an expanded range of wavelengths in the ultraviolet to violet region, in which an N2 laser is used for excitation. High lasing efficiencies were observed with αNPO‐dimethyl. POPOP, PPF‐αNPO, and some other dye mixtures, and overlapping lasing was observed, involving the donor and acceptor dye laser regions. A blue shift of the oscillation frequency was analyzed theoretically, and the theoretical results concerning the dependence of the oscillation wavelength on laser power and donor dye concentration were in good agreement with observations.