Optical absorption and stimulated emission of neodymium in yttriumorthosilicate

A spectroscopic investigation of the biaxial crystal yttrium orthosilicate doped with Nd³⁺(Nd³⁺:Y₂SiO₅) has been performed. Spectrally and orientationally resolved emission cross sections necessary for the evaluation of laser performance on the Nd^{3+ 4}F_3/2-⁴I _9/2 and ⁴F_3/2-⁴I_11/2 transitions have been determined. The Judd-Ofelt theory has been applied to measured values of optical absorption line strengths to obtain the orientation averaged intensity parameters: Ω₂-3.34×10^-20 cm², Ω ₄=4.35×10^-20 cm², and Ω₆=5.60×10^-20 cm². These Judd-Ofelt intensity parameter values are significantly different from those previously reported by A.M. Tkachuk et al. Using these intensity parameters, the Nd^{3+ 4}F₂ metastable state lifetime is predicted to be 225 μs. Measured low Nd concentration ⁴F_3/2 lifetimes of 214 μs indicate a high radiative quantum efficiency. Because of the Stark level splitting of the Nd^{3+ 4}F_3/2 and ⁴I_9/2 manifolds, laser operation at twice one of the Cs atomic resonance filter acceptance wavelengths is possible     

End-pumped Nd:LaF3 and Nd:LaMgAl11O19 lasers

Nd:LaF₃ and Nd:LaMgAl₁₁O₁₉ (LMA) are promising candidates for pulsed diode-laser-pumped lasers because they have relatively long upper state lifetimes and large absorption bandwidths compared to other Nd³⁺ doped materials. Crystal growth of LMA and the spectroscopic properties of both materials are described. Continuous-wave (CW) end-pumped lasers have been demonstrated in these materials using a Ti:Al₂O₃ laser to simulate the diode-laser pump source. Slope efficiencies of 47% for Nd:LaF₃ and 32% for Nd:LMA were obtained. The results for Nd:LaF₃ are typical for end-pumped, CW, Nd³⁺ lasers; the lower slope efficiency for Nd:LMA is attributed to excited-state absorption     

On the dynamics of population inversion for 3 μm Er3+lasers

A generalized model for 3-μm (⁴I_11/2 →⁴I_13/2)Er lasers is proposed. The essential energy transfer processes present in the single-doped Er ³⁺ systems (up-conversion from ⁴I_13/2, up-conversion from ⁴ I_11/2, cross-relaxation from ⁴S _3/2), as well as those present in Cr³⁺ codoped Er ³⁺ systems, are taken into account. In the frame of this model, the main features of 3 μm Er³⁺ lasers, such as long pulse or CW operation, the change of emission wavelength as a function of pumping conditions, and the effects of codoping with Ho³⁺ or Tm³⁺ ions, are explained     

The absorption and fluorescence spectra of rare earth ions insilica-based monomode fiber

Rare-earth ions have been systematically incorporated into the cores of silica-based optical fibers, and the absorption and fluorescence spectra have been measured. The results provide basic data for a wide range of possible future fiber-based devices. For specific telecommunications applications, ions that could be useful for sources in the 1.3-μm and 1.5-μm low-loss windows are identified. It is suggested that Er³⁺, Nd³⁺, and Tm³⁺ are the most promising ions for semiconductor pumping with GaAs-based laser diodes     

The sublinear relationship between index change and carrier densityin 1.5 and 1.3 μm semiconductor lasers

The carrier-induced index change was measured using a novel injection-reflection technique in combination with differential carrier lifetime data. The observed relation between index change and injected carrier density at bandgap wavelength is nonlinear and is approximately given by δn_act=-6.1×10^-14 ( N)^0.66 for a 1.5-μm laser and δn _act=-1.3×10^-14 (N)^0.68 for a 1.3-μm laser. The carrier-induced index change for a 1.3-μm laser at 1.53-μm wavelength is smaller and is given by δn _act=-9.2×10^-16 (N)^0.72      

Measurement of the stimulated emission cross section for the 4F3/2-4I13/2transition of Nd3+ in YAlO3 crystal

A method for the simultaneous measurement of the stimulated emission cross section and fluorescence lifetime by studying the relation between laser parameters and the laser relaxation oscillation frequency is discussed. The stimulated emission cross section for the ⁴F_3/2-⁴I_13/2 transition of Nd³⁺ ion in YAP crystal was measured to be (22±1)×10^-20 cm²     

Frequency stabilization of the sequence-band CO2 laserusing the 4.3-μm fluorescence method

The saturated 1.3-μm fluorescence stabilization method is applied to the 00⁰2-[10⁰1, 02⁰1]_I,II sequence band CO₂ laser transitions. For this purpose, the 4.3-μm fluorescence is observed using an external longitudinal CO₂ absorption cell heated to 300°C. The dependence of the frequency stability upon the gas temperature and pressure in the cell as well as laser parameters have been carried out in absolute frequency scale with the help of a two-channel heterodyne system. Under optimal conditions, the standard deviation of the beat note frequency between sequence band and regular band lasers for 30 s averaging time is less than 20 kHz, and the long-term stability and reproducibility is achieved at about 10 kHz     

8B9--Laser emission at 1.06 µ from Nd3+-Yb3+glass

Laser emission at 1.015 μm occurs in glass singly doped and when sensitized with Nd³⁺. For double doping in a Li Mg Al Si glass, emission at 1.015 μm from Yb³⁺and 1.06 μm from Nd³⁺was reported. By monitoring the 1.35 μm fluorescent line of Nd³⁺, it can be shown that both Nd³⁺and Yb³⁺lase at 1.06 μm at room temperature in a silicate glass with 5 weight percent Nd2O3and 5 weight percent Yb2O3. Energy transfer from Nd³⁺to Yb³⁺is a linear function of the Yb³⁺concentration. The transfer increases with Nd³⁺concentration by about a factor of three in going from 1 weight percent Nd2O3to 6 weight percent Nd2O3and thereafter remains approximately constant. This indicates that the transfer from Nd³⁺to Yb³⁺is assisted by intermediate transfer steps between Nd³⁺ions. Additional transfer above 6 weight percent Nd2O3is prevented by concentration quenching.     

Single-mode Nd3+-doped graded-index polymer waveguideamplifier

The first graded index (GRIN) polymer waveguide amplifier working at 1.06 μm wavelength has been realized, using a Nd³⁺: photolime gel material combination. Throughput intensity of 3.8 mW at 1.06 μm, corresponding to 8.5 dB gain, was observed when employing a 40 mW pumping laser beam operating at 790 nm. The gain medium is a 2.2 cm waveguide active region with Nd³⁺ concentration of 1.03×10²⁰/cm³. The GRIN characteristic of the photolime gel thin film provides a universal means for implementing polymer-based photonic integrated circuits (PICs) on any substrate of interest     

Characteristics of GaAsSb single-quantum-well-lasers emitting near1.3 μm

We report data on GaAsSb single-quantum-well lasers grown on GaAs substrates. Room temperature pulsed emission at 1.275 μm in a 1250-μm-long device has been observed. Minimum threshold current densities of 535 A/cm² were measured in 2000-μm-long lasers. We also measured internal losses of 2-5 cm^-1, internal quantum efficiencies of 30%-38% and characteristic temperatures T₀ of 67°C-77°C. From these parameters, a gain constant G₀ of 1660 cm^-1 and a transparency current density J_tr of 134 A/cm² were calculated. The results indicate the potential for fabricating 1.3-μm vertical-cavity surface-emitting lasers from these materials     

Y3MgAl3SiO12:Dy 3+,Eu 3+荧光粉的能量传递与暖白光实现

采用高温固相法合成了Dy ³⁺、Eu ³⁺共掺杂Y₃MgAl₃SiO₁₂石榴石型荧光粉。采用XRD、荧光光谱仪等仪器对样品的结构以及光谱特性进行表征,探究了Dy ³⁺/Eu ³⁺在Y₃MgAl₃SiO₁₂基质结构中的光谱特征以及离子间的能量传递机制。在367 nm近紫外光激发下,Y₃MgAl₃SiO₁₂:Dy ³⁺,Eu ³⁺的发射光谱包含Dy ³⁺的6F9/2到6H15/2和6H13/2的电子跃迁特征发射(487 nm蓝光和592 nm黄光)和Eu ³⁺的5D0 7F2 and 5D0 7F4特征发射峰(616 nm和710 nm红光)。在400~500 nm范围内Dy ³⁺发射谱与Eu ³⁺激发谱重叠,表明Dy ³⁺与Eu ³⁺之间存在着能量传递,能量传递的机理为电四极-电四极相互作用。该荧光粉通过调整Dy ³⁺和Eu ³⁺的掺杂浓度比封装近紫外LED芯片,可以实现单基质暖白光LED照明。     

Planar AlGaAs/GaAs heterojunction bipolar transistors fabricatedusing selective W-CVD

The authors describe a planar process for the AlGaAs/GaAs HBTs in which collector vias are buried selectively, even to the base layers, with chemical vapor deposited tungsten (CVD-W) films. By using WF₆ /SiH₄ chemistry, W could be deposited on Pt films, which were overlapped 50 nm thick on the AuGe-based collector electrodes, without depositing W on the surrounding SiO₂ layers. Current gains of planar HBTs with 3.5-μm×3.5-μm emitters were up to 150, for a collector current density of about 2.5×10⁴ A/cm²     

Spectroscopic properties and efficient diode-pumped laser operationof neodymium-doped lanthanum scandium borate

We report on the spectroscopic properties and laser performance of Czochralski-grown LaSc₃(BO₃)₄ (LSB) crystals with high neodymium concentrations up to 2.5·10²¹ cm^-3. The low-concentration quenching of the upper laser level of neodymium and the polarization dependence of the spectra indicate that LaSc₃(BO₃)₄ crystalizes in a huntite-type structure like Nd³⁺:YAl₃(BO₃)₄ (NYAB). With diode laser pumping at 808 nm, a multimode Nd³⁺:LaSc₃ (BO₃)₄ (NLSB) laser at 1063 nm is demonstrated. Optical slope efficiency was 64% with respect to absorbed pump power. The possibility of second-harmonic generation in the laser crystal is discussed     

Frequency measurements of 9- and 10-μm N2O lasertransitions

We have measured frequencies of N₂O transitions by heterodyning sub-Doppler fluorescence-stabilized N₂O laser radiation with that from a reference CO₂ laser. A high-resolution cavity incorporates a ribbed tube and a highly reflective grating, permitting the CW oscillation of both the 10⁰ 0-02⁰0 9-μm and the 10⁰0-00⁰1 10-μm regular bands. This is the first sub-Doppler frequency measurement of the 9-μm band. The accuracy in the determination of the rotational constants for both bands has been improved by an order of magnitude, and calculated transition frequencies are presented     

Fabrication of planar optical waveguides in LiB3O5 by 2 MeV He+ ion implantation

The fabrication of planar optical waveguides in LiB₃O ₅ is discussed. Using 2-MeV ⁴He⁺ implantation with a dose of 1.5×10¹⁶ ions/cm² at 300 K, the refractive indexes of a 0.2-μm-thick layer 5.1 μm below the crystal surface are reduced to form optical barrier guides. For this ion dose the maximum change from the bulk values of refractive index at a wavelength of 0.488 μm are 1.5%, 5.25%, and 4% for n_x, n_y, and n_z, respectively. The refractive indexes of the guiding region change by less than 0.02% from the bulk values. The dose dependence of the optical barrier height has been measured. A threshold ion dose of about 0.75×10¹⁶ ions/cm² is required to form a refractive index barrier and ion doses higher than about 2.5×10¹⁶ ions/cm². saturate the refractive index decrease. Waveguide propagation losses for annealed single energy implants of dose 1.5×10¹⁶ ions/cm² are dominated by tunneling and are estimated to be ~8.9 dB/cm for the z-cut waveguides used. Multiple energy implants broaden the optical barrier, and losses of <4 dB/cm have been observed     

Monolithic photovoltaic PbS-on-Si infrared-sensor array

The growth of epitaxial narrow-gap PbS-on-Si substrates using a stacked CaF₂-BaF₂ intermediate buffer layer and the fabrication of linear arrays of photovoltaic infrared (IR) sensors in the PbS layer are discussed. The sensors of the array exhibit resistance-area products at zero bias of 3 Ω-cm² at 200 K (3.4-μm cutoff wavelength) and 2×10⁵ Ω-cm ² at 84 K (4-μm cutoff), with corresponding detectivities of 2×10¹⁰ and 1×10¹³ cm-√Hz/W, respectively     

Emission cross sections and spectroscopy of Ho3+ laserchannels in KGd(WO4)2 single crystal

The spectroscopic properties of Ho³⁺ laser channels in KGd(WO₄)₂ crystals have been investigated using optical absorption, photoluminescence, and lifetime measurements. The radiative lifetimes of Ho³⁺ have been calculated through a Judd-Ofelt (JO) formalism using 300-K optical absorption results. The JO parameters obtained were Ω₂=15.35×10^-20 cm², Ω ₄=3.79×10^-20 cm², Ω₆ =1.69×10^-20 cm². The 7-300-K lifetimes obtained in diluted (8·10¹⁸ cm^-3) KGW:0.1% Ho samples are: τ(⁵F₃)≈0.9 μs, τ( ⁵S₂)=19-3.6 μs, and τ(⁵F₅ )≈1.1 μs. For Ho concentrations below 1.5×10²⁰ cm^-3, multiphonon emission is the main source of non radiative losses, and the temperature independent multiphonon probability in KGW is found to follow the energy gap law τ_ph ^-1(0)=βexp(-αΔE), where β=1.4×10^-7 s^-1, and α=1.4×10³ cm. Above this holmium concentration, energy transfer between Ho impurities also contributes to the losses. The spectral distributions of the Ho³⁺ emission cross section σ_EM for several laser channels are calculated in σ- and π-polarized configurations. The peak a σ_EM values achieved for transitions to the ⁵I₈ level are ≈2×10^-20 cm² in the σ-polarized configuration, and three main lasing peaks at 2.02, 2.05, and 2.07 μm are envisaged inside the ⁵I₇→⁵I₈ channel     

5 Gb/s optical soliton transmission experiment using Ramanamplification for fiber-loss compensation

Optical soliton transmission of 5 Gb/s over a 23-km amplification spacing using a gain-switched 1.55-μm distributed feedback laser diode and Ti:LiNbO₃ intensity modulator is discussed. An Er ⁺-doped fiber amplifier, pumped by 1.45- and 1.48-μm laser diodes, is employed for achieving intense optical pulses. Transmission fiber-loss is completely compensated for by Raman amplification using by 1.45- and 1.48-μm laser-diode pumping. A bit error rate (BER) of 2×10^-10 has been obtained     

Optimization of a self-aligned titanium silicide process forsubmicron technology

The optimization of a manufacturable self-aligned titanium silicide process is described. In particular, the integrity of the TiSi ₂ layer has been studied versus the BPSG reflow conditions. Excellent contact resistance and very low leakage currents have been obtained. The good device parameters obtained with an n⁺ or n ⁺/p⁺ gate have demonstrated that the self-aligned process can be integrated in a 0.8-μm double-metal CMOS process     

Repetitively pulsed Nd-glass slab lasers

The possibility of obtaining high laser output energies at a 1.32-μm wavelength using thin LiNdLa phosphate glass slabs with a high Nd³⁺ concentration is discussed. In the experiments, 3×14×125-mm slabs were prepared from LiNdLa phosphate glass with a Nd-concentration of 1.2×10²¹ cm^-3. The facets of the slabs were not antireflection-coated. They were tested in a silver-coated quartz tube reflector of 25-mm diameter and pumped by 450-μs pulses from a flash lamp with a 120-mm arc length. In this construction the light, which passes through the slab, returns to it after reflection from the tube surface. Most of the radiation falls on the wider side of the slab at large angles of incidence, thus maximizing its path inside the slab. The quartz reflector was water cooled. The 150-mm laser resonator was formed by two flat mirrors. At 1.32-μm lasing wavelength an output mirror of r=95% reflectivity was used with less than 10% reflectivity at 1.32 μm