Modeling and optimization of cascaded erbium and holmium doped fluoride fiber lasers

Numerical modeling of cascade erbium-doped and holmium-doped fluoride fiber lasers is presented. Fiber lengths were optimized for cascade lasers that had fixed or free-running wavelengths using all known spectroscopic parameters. The performance of the cascade laser was tested against dopant concentration, energy transfer process, heat generation, output coupling, and pump schemes. The results suggest that the slope efficiencies and thresholds for both transitions increase with increasing Ho3+ or Er3+ concentration with the slope efficiency stabilizing after 1 mol% rare earth doping. The heat generation in the Ho3+-based system is lower compared to the Er 3+-based system at low dopant concentration as a result of the lower rates of multiphonon relaxation. Decreasing the output coupling for the upper (∼3 μm) transition decreases the threshold of the lower transition and the upper transition benefits from decreasing the output coupling for the lower transition for both cascade systems. The highest slope efficiency was achieved under counter-propagating pump conditions. Saturation of the output power occurs at comparatively higher pump power with dilute Er3+ doping compared with heavier doping. Overall, we show that the cascade Ho3+ -doped fluoride laser is the best candidate for high power output because of its higher slope efficiency and lower temperature excursion of the core and no saturation of the output. © 2013 IEEE.

Mid-infrared passively switched pulsed dual wavelength Ho3+ -doped fluoride fiber laser at 3 μm and 2 μm

Cascade transitions of rare earth ions involved in infrared host fiber provide the potential to generate dual or multiple wavelength lasing at mid-infrared region. In addition, the fast development of saturable absorber (SA) towards the long wavelengths motivates the realization of passively switched mid-infrared pulsed lasers. In this work, by combing the above two techniques, a new phenomenon of passively Q-switched ~3 μm and gain-switched ~2 μm pulses in a shared cavity was demonstrated with a Ho3+-doped fluoride fiber and a specifically designed semiconductor saturable absorber (SESAM) as the SA. The repetition rate of ~2 μm pulses can be tuned between half and same as that of ~3 μm pulses by changing the pump power. The proposed method here will add new capabilities and more flexibility for generating mid-infrared multiple wavelength pulses simultaneously that has important potential applications for laser surgery, material processing, laser radar, and free-space communications, and other areas.

Spectrum-, pulsewidth-, and wavelengthswitchable all-fiber mode-locked Yb laser with fiber based birefringent filter

We examined methods of controlling the pulse duration, spectral width and wavelength of the output from an all-fiber Yb laser mode-locked by carbon nanotubes. It is shown that a segment of polarization maintaining (PM) fiber inserted into a standard single mode fiber based laser cavity can function as a spectral selective filter. Adjustment of the length of the PM fiber from 1 to 2 m led to a corresponding variation in the pulse duration from 2 to 3.8 ps, the spectral bandwidth of the laser output changes from 0.15 to 1.26 nm. Laser output wavelength detuning within up to 5 nm was demonstrated with a fixed length of the PM fiber by adjustment of the polarization controller. © 2012 Optical Society of America.

Different generation regimes of mode-locked all-positive-dispersion all-fiber Yb laser

Different generation modes of all-positive-dispersion all-fibre Yb laser mode-locked due to effect of non-linear polarization evolution are investigated. For the first time we realized in the same laser both generation of single picoseconds pulse train and a newly observed lasing regime where generated are picosecond wave-packets, each being a train of femtosecond sub-pulses. Using both experimental results and numerical modeling we discuss in detail the mechanisms of laser mode-locking and switching of generation regimes and show a strong dependence of output laser characteristics on configuration of polarization controllers. A good qualitative agreement between experimental results and numerical modeling is demonstrated. © 2010 Copyright SPIE - The International Society for Optical Engineering.

Simultaneous Measurement of Strain and Temperature using Type I and Pre-strained Fiber Bragg Gratings

Strain and temperature sensitivities of a type I Bragg grating inscribed in a germania doped silica fiber, fabricated under normal conditions and zero strain, are compared with that of a Bragg grating inscribed under pre-strained condition. The results obtained reveal that the strain and temperature sensitivities of the two gratings are different. Based on these results, we demonstrate a technique which enables discrimination of strain and temperature in a Fiber Bragg Grating (FBG) with a linear response. The present technique allows for an easy implementation of the sensor by providing a direct access to the grating region in the fiber and demands only a simple interrogation system.

Direct ultrafast laser written C-band waveguide amplifier in Er-doped chalcogenide glass

This paper reports the fabrication and characterization of an ultrafast laser written Er-doped chalcogenide glass buried waveguide amplifier; Er-doped GeGaS glass has been synthesized by the vacuum sealed melt quenching technique. Waveguides have been fabricated inside the 4 mm long sample by direct ultrafast laser writing. The total passive fiber-to-fiber insertion loss is 2.58 +/- 0.02 dB at 1600 nm, including a propagation loss of 1.6 +/- 0.3 dB. Active characterization shows a relative gain of 2.524 +/- 0.002 dB/cm and 1.359 +/- 0.005 dB/cm at 1541 nm and 1550 nm respectively, for a pump power of 500 mW at a wavelength of 980 nm. (C) 2012 Optical Society of America

In-doped multifilled n-type skutterudites with ZT=1.8

In this paper we maximize the thermoelectric (TE) figure of merit, ZT, of n-type skutterudites, (In,Sr,Ba,Yb)(y)Co4Sb12, via three different routes: (i) find the optimum fraction of In as fourth filler (ii) check the influence of powder particle, grain, and crystallite size on the TE properties and (iii) check thermal stability. Filled n-type (Sr, Ba, Yb)(y)Co4Sb12 was mixed in three different proportions with In0.4Co4Sb12, ball milled (regular or high-energy (HB) ball milling) and hot-pressed. Particle size analyses and SEM pictures of the broken surfaces of the hot pressed samples document that only HB produces uniform particles/grains with average crystallite sizes similar to 100 nm, proven by transmission electron microscopy. X-ray Rietveld refinements combined with EDX indicate that in all cases indium entered the icosahedral voids of the skutterudite. Temperature dependent physical properties of all three regularly ball-milled samples show that increasing In-content infers an increasing electrical resistivity, increasing Seebeck coefficient but a decreasing total thermal conductivity. Although ZT (823 K) is in the same range as for the sample without In, the ZT values in the whole temperature range are higher and consequently the TE-conversion efficiency, eta is at least 10% higher. Annealing the samples at 600 degrees C for three days shows minor changes in structure and thermoelectric properties, indicating TE stability. The HB sample, due to uniformly small particles, equally sized grains and crystallites, exhibits a high power factor (4.4 mW/m K-2 at 730 K) and a very low thermal conductivity leading to an outstanding high ZT = 1.8 at 823 K (eta(max) = 17.5%). (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

激光二极管抽运的国产Yb:YAG陶瓷激光器

研究了国产Yb:YAG陶瓷的激光输出特性。激光器采用激光二极管(LD)纵向同轴抽运Yb:YAG陶瓷样品,样品的掺杂原子数分数为1%,一端面镀940 nm和1030 nm双增透膜,另一端面镀1030 nm增透膜,激光器在1031 nm处获得了近红外激光输出。实验中分别测试了Yb:YAG陶瓷在不同输出透射率(T=4%,8%,10%)条件下的激光输出特性。整个实验过程中,激光器维持基横模运转。当输出透射率为10%,吸收的抽运功率为9 W时,激光器获得最大的激光输出功率为1.63 W,相应的斜率效率为23.2%。

Optical properties of transparent alkali gallium silicate glass-ceramics containing Ni2+-doped beta-Ga2O3 nanocrystals

Broadband near-infrared (IR) luminescence in transparent alkali gallium silicate glass-ceramics containing N2+-doped beta-Ga2O3 nanocrystals was observed. This broadband emission could be attributed to the T-3(2g) (F-3) -> (3)A(2g) (F-3) transition of octahedral Ni2+ ions in glass-ceramics. The full width at half-maximum (FWHM) of the near-IR luminescence and fluorescent lifetime of the glass-ceramic doped with 0.10 mol% NiO were 260 nm and similar to 1220 mu s, respectively. It is expected that transparent Ni2+-doped beta-Ga2O3 glass-ceramics with this broad near-IR emission and long fluorescent lifetime have potential applications as super-broadband optical amplification media.

Improved fluorescence from Tm3+/Er3+/Ce3+ triply doped bismuth-silicate glasses for S+C-bands amplifiers

Fluorescence of Tm3+/Er3+ codoped bismuth-silica (BS) glasses and the sensitization of Ce3+ are investigated. It shows that Ce3+ codoping with Tm3+/Er3+ in BS glasses results in a quenching of Tm3+ ion emission from F-3(4) to the H-3(6) level. Consequently, the 1.47 mu m emission occurs after the population inversion between the H-3(4) and F-3(4) levels. Furthermore, the codoped glasses show the broad emission spectra over the whole S and C bands with full-width at half-maximum (FWHM) up to about 119nm, as it combines 1.55 mu m emission band of Er3+ with 1.47 mu m emission band of Tm3+ under 800nm excitation.

Wavefront measurement of double-clad pulsed ytterbium fiber laser

Because of high efficiencies, compact structure, and excellent heat dissipation, high-power fiber lasers are extremely useful for applications such as cutting, welding, precision drilling, trimming, sensing, optical transmitter, material processing, micromachining, and so on. However, the wavefront of the double clad fiber laser doped with ytterbium is still unknown. In this paper, wavefront of a fiber laser is measured and the traditional Hartmann-shack wavefront sensing method is adopted. We measured a double clad fiber laser doped with ytterbium which produces pulse wave output at infrared wavelength. The wavefront shape and contour are reconstructed and the result shows that wavefront is slightly focused and not an ideal plane wavefront. Wavefront measurement of fiber laser will be useful to improving the lasers' performance and developing the coherent technique for its applications.

Strong visible up-conversion emissions and thermometric applications of Er3+-Yb3+ codoped Al2O3 prepared by the sol-gel method

The Er3+-Yb3+ codoped Al2O3 has been prepared by the sol-gel method using the aluminium isopropoxide [Al(OC3H7)(3)]-derived Al2O3 sols with addition of the erbium nitrate [Er(NO3)(3) center dot 5H(2)O] and ytterbium nitrate [Yb(NO3)(3) center dot 5H(2)O]. The phase structure, including only two crystalline types of doped Al2O3 phases, theta and gamma, was obtained for the 1 mol% Er3+ and 5 mol% Yb3+ codoped Al2O3 at the sintering temperature of 1,273 K. By a 978 nm semiconductor laser diodes excitation, the visible up-conversion emissions centered at about 523, 545, and 660 nm were obtained. The temperature dependence of the green up-conversion emissions was studied over a wide temperature range of 300-825 K, and the reasonable agreement between the calculated temperature by the fluorescence intensity ratio (FIR) theory and the measured temperature proved that Er3+-Yb3+ codoped Al2O3 plays an important role in the application of high temperature sensor.

两根掺镱大芯双包层光纤激光器获得113W同相输出功率

利用一个自成像共焦腔和一个空间滤波器实现了两掺Yb大芯光纤激光器的位相锁定。观测到稳定的具有高对比度的干涉条纹。相干条纹的对比度为59%，而非相干时对比度为6%。中心条纹的宽度与理论计算结果吻合得很好。对同相模式而言，位相锁定激光器阵列输出达到113W，对应的斜率效率为38.5%。

133-W pulsed fiber amplifier with large-mode-area fiber

A master-oscillator fiber power amplifier (MOPA) system with a 4-m-long Yb3+-doped homemade large mode area (LMA) double-clad fiber is reported. The system emits up to 133.8 W of amplified radiation at a wavelength of 1064 nm and a repetition rate of 100 kHz, limited only by the available pump power. Peak power of 300 kW at 20 kHz with a pulse duration of 15 ns is obtained. (c) 2006 Society of Photo-Optical Instrumentation Engineers.