Evaporation characteristics of Er3+-doped silica fiber and its application in the preparation of whispering gallery mode lasers.

In this work, the concentration of rare-earth ions in doped silica whispering gallery lasers (WGLs) is controlled by evaporation. The fabrication of WGLs is used to experimentally evaluate the evaporation rate (mol/µm) and ratio (mol/mol) of erbium and silica lost from a doped fiber during heating. Fixed lengths of doped silica fiber are spliced to different lengths of undoped fiber and then evaporated by feeding into the focus of a CO2 laser. During evaporation, erbium ions are precipitated in the doped silica fiber to control the erbium concentration in the remaining SiO2, which is melted into a microsphere. By increasing the length of the undoped section, a critical point is reached where effectively no ions remain in the glass microsphere. The critical point is found using the spectra of the whispering gallery modes in microspheres with equal sizes. From the critical point, it is estimated that, for a given CO2 laser power, 6.36 × 10-21 mol of Er3+ is lost during the evaporation process for every cubic micron of silica fiber. This is equivalent to 1.74 × 10-7 mol of Er3+ lost per mol of SiO2 evaporated. This result facilitates the control of the doping concentration in WGLs and provides insight into the kinetics of laser-induced evaporation of doped silica.

PDA modified NIR-II NaEr0.8Yb0.2F4nanoparticles with high photothermal effect.

Polydopamine (PDA)-modified NaEr0.8Yb0.2 F4nanoparticles were synthesized, with strong NIR-II emission, quantum yield of 29.63%, and excellent photothermal performance. Crystal phases and microstructures are characterized. Optical properties such as absorption, NIR-II emission, and light stability are studied, and the luminescence mechanism is discussed in detail. Key factors in NIR-II imaging were evaluated in fresh pork tissue, including penetration depth, spatial resolution, and signal-to-noise ratio (SNR). A high penetration depth of 5 mm and a high spatial resolution of 1 mm were detected. Mice are imaged in vivo afterintravenousinjection. Due to the accumulation of nanoparticles in the liver, high image quality with an SNR of 5.2 was detected in the abdomen of KM mice with hair. The photothermal conversion effect of PDA-modified NPs was twice that of the reported material. These NIR-II nanoparticles have superior optical properties, high photothermal efficiency and low cytotoxicity, and are potential fluorescent probes for further disease diagnosis and treatment.

Ultra-low-loss double-cladding laser fiber fabricated by optimized chelate gas phase deposition technique.

By applying an optimized chelate gas phase deposition technique, a Yb/Ce codoped aluminosilicate fiber with ultra-low loss of 1.55 dB/km was successfully fabricated and reported. The fiber showed homogenous distribution of the refractive index and dopant concentration devoid of central dip and clustering. Using the fiber as the amplifier stage, it delivered 1023 W near-single-mode laser output (M2=1.35) with a high slope efficiency of 85.1%, and the fiber temperature was less than 24.2°C, primarily benefiting from the ultra-low background loss. The fiber also exhibited low photodarkening-induced loss, illustrating its outstanding photodarkening resistance. These results indicate that the ultra-low-loss Yb/Ce codoped aluminosilicate fiber is a prospective candidate for stable and reliable fiber laser applications.

Fundamental-frequency-absorbed oxyfluoride glass in a high-power laser.

A high-power third-harmonic laser faces challenges in the filtering remnant unconverted fundamental frequency, which is from the frequency converting crystal. In this work, a novel fundamental-frequency-absorbed oxyfluoride glass has been prepared, which provides a possible option to solve the problem. By being doped with Fe2+ ion, the glass shows strong absorption property at 1053 nm, and the glass's transmittances at 351 and 1053 nm are stable with changing the laser power or increasing the irradiation times under high-power laser irradiation. Meanwhile, the laser-induced damage threshold of the glass is 12.5 J/cm2 at 351 nm, which is two times higher than that of fused silica whose threshold is 6.2 J/cm2 in the same testing condition. The glass also exhibits a higher laser-induced damage threshold as well as 36.6 J/cm2 at its absorption wavelength of 1053 nm. The results indicate that this glass is promising as a color-separation optic, thus allowing a novel design for the final optics assembly in an inertial confinement fusion laser system.

Luminescence in the fluoride-containing phosphate-based glasses: a possible origin of their high resistance to nanosecond pulse laser-induced damage.

Fusion power offers the prospect of an almost inexhaustible source of energy for future generations. It was reported that fusion fuel gains exceeding unity on the National Ignition Facility (NIF) were achieved, but so far great deal of scientific and engineering challenges have to be overcome for realizing fusion power generation. There is a bottleneck for color-separation gratings in NIF and other similar inertial confinement fusion (ICF) lasers. Here we show a series of high performance phosphate-based glasses that can transmit the third harmonic frequency (3ω) laser light with high efficiency meanwhile filter the fundamental (1ω) and the second harmonic frequency (2ω) laser lights through direct absorption, and especially they exhibit excellent damage threshold induced by nanosecond pulse laser compared with that of the fused silica used in NIF. Yellowish-orange fluorescence emits during the laser-material interaction process, and it can be tailored through regulating the glass structure. Study on its structural origin suggests that the fluorescence emission is a key factor that conduces to the high laser-induced damage resistance of these glasses. The results also indicated the feasibility of utilizing these high performance glasses in novel color separation optics, allowing novel design for the final optics assembly in ICF lasers.

Effects of the host morphologies on luminescence properties of Nd(3+)-doped LaF3 nanoparticles.

By using different surfactants, several host morphologies including rod-like, pot-like and shuttle-like of LaF3:Nd3+(1% mol) nanoparticles were prepared by a simple microemulsion hydrothermal method, and their properties were characterised by XRD, TEM and photoluminescence spectroscopy. The experimental results indicated that the rod-like and pot-like nanocrystals possess well shaped hollow structures. The analysis of spectra proved that the local environment around the dopant ion changed with the different host morphology, which in turn influenced the luminescence properties. The luminescence lifetimes derived from biexponential fitting were 615 micros (nanopots), 419 micros (nanorods) and 194 micros (nanoshuttles), respectively. This phenomenon is ascribed to the weakening effect of hollow or fenestral structures to the nonradiative ratio.

Third-order nonlinear optical properties of GeS(2)-Sb(2)S(3)-CdS chalcogenide glasses.

The third-order nonlinear optical properties of GeS(2)-Sb(2)S(3)-CdS chalcogenide glasses were investigated utilizing the Z-scan and femtosecond time-resolved optical Kerr effect (OKE) methods at the wavelength of 800 nm, respectively. The compositional dependences were analyzed and the influencing factors including the linear refractive index, the concentration of lone electron pairs, the optical bandgap and the amount of weak covalent/ homopolar bonds were discussed. A glass, i.e. 76GeS(2)·19Sb(2)S()·5CdS, with large nonlinear refrative index (n(2) = 5.63 × 10(-14) cm(2)/W), low nonlinear absorption coefficient (ß = 0.88 cm/GW) and minimum figure of merit (FOM = 2ßλ/n(2) = 2.51) was finally prepared. The electronic contribution in weak heterpolar covalent and homopolar bonds are responsible for large n(2) in chalcogenide glass, and the Sheik-Bahae rule combining the Moss rule are proved to be an effective guidance for estimating the third-order nonlinearities and further optimizing the compositions in chalcogenide glasses.

Effects of organic surfactant on fluorescence concentration quenching of Nd(3+)-doped LaF(3) nanoparticles.

Distinct effects of organic surfactant [ammonium di-n-octadecyldithioposhate (ADDP)] on the fluorescent property of Nd(3+)-doped LaF(3) nanoparticles were demonstrated by incorporating different amounts of organic surfactant on the nanoparticles. The photoluminescence spectra and fluorescence quenching concentrations of the nanoparticles were measured. A high fluorescence quenching concentration (of about 23.4 wt.%) for the LnF(2.36)ADDP(0.64) nanoparticles was observed. The quenching concentration could be adjusted by varying the amount of organic surfactant. This phenomenon is ascribed to the protection of organic surfactants coordinated on nanoparticles' fluorescent centers.

Host dependence of spectroscopic properties of Dy 3+ - doped and Dy 3+, Tm 3+ -codped Ge-Ga-S-CdI 2 chalcohalide glasses.

Two serial Dy(3+)-doped and Dy(3+), Tm(3+)-codoped (100-x)(0.8GeS(2).0.2Ga(2)S(3)).xCdI(2) (0Dy(3+): 6H 11/2 energy transfer efficiency and intensified the mid-infrared emissions. The emission cross sections (sigma emi) of the 2900 and 4300 nm fluorescences were estimated to be 1.68 x 10(-20) and 1.20 x 10(-20)cm(2) respectively for the 0.2 wt% Dy(3+) and 0.5 wt% Tm(3+) codoped 64 GeS(2).16 Ga(2)S(3).20 CdI(2) glass. These novel chalcohalide glasses are promising candidate materials for fiber-amplifiers and mid-infrared laser devices.

Broad-spectrum and long-lifetime emissions of Nd3+ ions in lead fluorosilicate glass.

A novel Nd(3+)-doped lead fluorosilicate glass (NPS glass) is prepared by a two-step melting process. Based on the absorption spectrum a Judd-Ofelt theory analysis is made. The emission line width of NPS glass is 44.2 nm. The fluorescence decay lifetime of the (4)F(3/2) level is 586+/-20 microsec, and the stimulated emission cross-section is 0.87x10(-20)cm(2)at 1056 nm. A laser oscillation is occurred at 1062 nm when pumped by 808 nm Diode Laser. The slope efficiency is 23.7% with a 415 mJ threshold. It is supposed that NPS glass is a good candidate for using in ultra-short pulse generation and amplification by the broad emission bandwidth and long fluorescence lifetime.