Nonradiative relaxation and laser action in tunable solid state laser crystals

Room-temperature pulsed laser action was obtained in chromium-activated forsterite (Cr:Mg2SiO4) for both 532 and 1064 nm pumping. Free running laser emission in both cases is centered at 1235 nm and has a bandwidth of approximately 30 nm. Slope efficiency as high as 22 percent was measured. Using different sets of output mirrors and a single birefrigent plate as the intracavity wavelength selecting element tunability over the 1167 to 1268 nm spectral range was demonstrated. Continuous wave laser operation at room temperature was obtained for 1064 nm pumping from a CW Nd:YAG laser. The output power slope efficiency is 6.8 percent. The gain cross section is estimated to be 1.1 x 10 to the 19th sq cm. Spectroscopic studies suggest that the laser action is due to a center other than the trivalent chromium (Cr 3+), presumably the tetravalent chromium (Cr 4+) in a tetrahedrally coordinated site

Tetravalent chromium doped laser materials and NIR tunable lasers

A method is described to improve and produce purer Cr.sup.4+-doped laser materials and lasers with reduced co-incorporation of chromium in any other valence states, such as Cr.sup.3+, Cr.sup.2+, Cr.sup.5+, and Cr.sup.6+. The method includes: 1) certain crystals of olivine structure with large cation (Ca) in octahedral sites such as Cr.sup.4+:Ca.sub.2GeO.sub.4, Cr.sup.4+:Ca.sub.2SiO.sub.4, Cr.sup.4+:Ca.sub.2Ge.sub.xSi.sub.1-xO.sub.4 (where 0<x<1), and/or 2) high-temperature solution growth techniques that enable the growth of the crystals below the temperature of polymorphic transitions by using low melting point solvent based on oxide, fluoride and/or chloride compounds. Purer Cr.sup.4+-doped laser materials are characterized by a relatively high concentration of Cr.sup.4+-lasing ion in crystalline host that makes these materials suitable for compact high power (thin disk/wedge) NIR laser applications

Cr.sup.4+-doped mixed alloy laser materials and lasers and methods using the materials

A laser medium includes a single crystal of Cr.sup.4+:Mg.sub.2-xM.sub.xSi.sub.1-yA.sub.yO.sub.4, where, where M is a bivalent ion having an ionic radius larger than Mg.sup.2+, and A is a tetravalent ion having an ionic radius larger than Si.sup.4+. In addition, either a) 0.ltoreq.x<2 and 0<y<1 or b) 0<x<2 and y is 0 or 1 with the proviso that if M is Ca.sup.2+ and x=1 then y is not 0. The laser medium can be used in a laser device, such as a tunable near infrared (NIR) laser

Cr.sup.3+-doped laser materials and lasers and methods of making and using

A laser medium includes a single crystal of chromium-doped LiSc.sub.l-xIn.sub.xGe.sub.1-ySi.sub.yO.sub.4, where 0.ltoreq.x.ltoreq.1 and 0.ltoreq.y.ltoreq.1. Preferably, x and y are not both 0. A laser, such as a tunable near infrared laser, can contain the laser medium

Tetravalent Chromium (Cr(4+)) as Laser-Active Ion for Tunable Solid-State Lasers

During 10/31/92 - 3/31/93, the following summarizes our major accomplishments: (1) the self-mode-locked operation of the Cr:forsterite laser was achieved; (2) synchronous pumping was used to mode lock the forsterite laser resulting in picosecond pulses, which in turn provided the starting mechanism for self-mode-locking; and (3) the pulses generated had a FWHW of 105 fs and were tunable between 1230 - 1270 nm

Tetravalent Chromium (Cr(4+)) as Laser-Active Ion for Tunable Solid-State Lasers

During 10/31/91 - 3/31/92, the following summarizes are major accomplishments: (1) numerical modeling of the four mirror astigmatically compensated, Z-fold cavity was performed; and (2) the simulation revealed several design parameters to be used for the construction of a femtosecond forsterite laser

Tetravalent chromium (Cr(4+)) as laser-active ion for tunable solid-state lasers

Major accomplishments under NASA grant NAG-1-1346 are summarized. (1) numerical modeling of the four mirror astigmatically compensated, Z-fold cavity was performed and several design parameters to be used for the construction of a femtosecond forsterite laser were revealed by simulation. (2) femtosecond pulses from a continuous wave mode-locked chromium doped forsterite laser were generated. The forsterite laser was actively mode-locked using an acousto-optic modulator operating at 78 MHz with two Brewster high dispersion glass prisms for intra-cavity chirp compensation. Transform-limited sub-100-fs pulses were routinely generated in the TEM(sub 00) mode with 85 mW of continuous power tunable over 1230-1280 nm. The shortest pulses of 60-fs pulsewidth were measured. (3) Self-mode-locked operation of the Cr:forsterite laser was achieved. Synchronous pumping was used to mode lock the forsterite laser resulting in picosecond pulses, which in turn provided the starting mechanism for self-mode-locking. The pulses generated had an FWHM of 105 fs and were tunable between 1230-1270 nm. (4) Numerical calculations indicated that the pair of SF 14 prisms used in the cavity compensated for quadratic phase but introduced a large cubic phase term. Further calculations of other optical glasses indicated that a pair of SFN 64 prisms can introduce the same amount of quadratic phase as SF 14 prisms but introduce a smaller cubic phase. When the SF 14 prisms were replaced by SFN 64 prisms the pulsewidth was reduced to 50 fs. Great improvement was observed in the stability of the self mode-locked forsterite laser and in the ease of achieving mode locking. Using the same experimental arrangement and a new forsterite crystal with improved FOM the pulse width was reduced to 36 fs

Tetravalent chromium (Cr(4+)) as laser-active ion for tunable solid-state lasers

Generation of femtosecond pulses from a continuous-wave mode-locked chromium-doped forsterite (Cr(4+):Mg2SiO4) laser has been accomplished. The forsterite laser was actively mode-locked using an acousto-optic modulator operating at 78 MHz with two Brewster high-dispersion glass prisms for intra-cavity chirp compensation. Transform-limited sub-100-fs pulses were routinely generated in the TEM(sub 00) mode with 85 mW of continuous power (with 1 percent output coupler), tunable over 1230-1280 nm. The shortest pulses of 60-fs pulsewidth were measured

Relationship between optical transparency and nanostructural features of silica aerogels

Abstract Silica aerogels are considered to be of great promise for use in transparent thermal insulation systems in solar architecture. The optical transparency of these highly porous materials is influenced by the reaction parameters upon preparation and the precursor used. Previously it was shown that the specific extinction due to bulk scattering decreases both with increasing macroscopic density and increasing pH-value of the sol-gel starting solution. Recently, it was also found that within the measurement accuracy the light scattering intensity of the aerogel bulk equals the extrapolated small-angle X-ray scattering intensity towards scattering angle zero if both types of measurement are performed with respect to an absolute scale. In the meantime, ultra small-angle X-ray scattering measurements have been performed in order to close the gap in momentum space between light and conventional small-angle X-ray scattering. As a result it can be stated that the nearly isotropic (Rayleigh) scattering is caused by the same nanostructural inhomogeneities of the aerogel network which lead to the characteristic small-angle scattering pattern. As a consequence, the amount of isotropically scattered light and thus the optical extinction can be directly related to a quantity called the correlation volume. For a variety of silica aerogels, it is shown how the latter depends on the nanostructural features of the gel network, such as average particle size, interparticle arrangement, pore diameter and an ordering parameter, which accounts for concentration effects

Using an in-vitro biofilm model to assess the virulence potential of Bacterial Vaginosis or non-Bacterial Vaginosis Gardnerella vaginalis isolates

Gardnerella vaginalis is the most common species found in bacterial vaginosis (BV). However, it is also present in a significant proportion of healthy women and G. vaginalis vaginal colonization does not always lead to BV. In an effort to better understand the differences between G. vaginalis isolated from women with a positive (BV) versus a negative (non-BV) diagnosis of BV, we compared the virulence potential of 7 BV and 7 non-BV G. vaginalis isolates and assessed the virulence factors related to biofilm formation, namely: initial adhesion and cytotoxic effect, biofilm accumulation, susceptibility to antibiotics, and transcript levels of the known vaginolysin, and sialidase genes. Furthermore, we also determined the ability of G. vaginalis to displace lactobacilli previously adhered to HeLa cells. Our results showed that non-BV strains were less virulent than BV strains, as suggested by the lower cytotoxicity and initial adhesion to Hela cells. Significant differences in expression of known virulence genes were also detected, further suggesting a higher virulence potential of the BV associated G. vaginalis. Importantly, we demonstrated that BV associated G. vaginalis were able to displace pre-coated vaginal protective lactobacilli and we hypothesize this to be a trigger for BV development.European Union funds (FEDER/COMPETE) and by national funds (FCT) under the project with reference FCOMP-01-0124-FEDER-008991 (PTDC/BIA-MIC/098228/2008). FCT Strategic Project of UID/BIO/04469/2013 unit the project NORTE-07-0124-FEDER-000027, co-funded by the Programa Operacional Regional do Norte(ON.2 – O Novo Norte), QREN, FEDER, and the project RECI/BBB-EBI/0179/2012 (FCOMP-01-0124-FEDER-027462). FCT individual fellowship SFRH/BD/93963/2013