Red, Green, and Blue Light Through Cooperative Up-Conversion in Sol-Gel Thin Films Made With Yb0.80La0.15Tb0.05F3 and Yb0.80La0.15Eu0.05F3 Nanoparticles

Silica and zirconium dioxide sol-gel thin films made with Yb_0.80La_0.15Tb_0.05F₃ or Yb _0.80La_0.15Eu_0.05F₃ nanoparticles are reported. Bright blue (413 and 435 nm), green (545 nm), and red (585 and 625 nm) emissions are produced from Tb³⁺ ions through cooperative up-conversion of 980 nm light. Similarly, red (591 and 612 nm) emission is generated from Eu³⁺ ions. These up-convertors may find use in white light sources. The cooperative up-conversion of Yb³⁺-Tb³⁺ ions is more efficient than of Yb³⁺-Eu³⁺ ions because the efficiency of energy transfer from excited Yb³⁺ ions to a Tb ³⁺ ion (0.37) is more than two-times higher than of excited Yb³⁺ ions to a Eu³⁺ ion (0.15), as estimated from the lifetime of excited Yb³⁺ ion. The estimated quantum yields of both Tb³⁺ ion and Eu³⁺ ion emissions are on the order of 40%, and hence are not the cause of the difference in efficiency. This approach does not work for Sm³⁺, Pr³⁺ , and Dy³⁺. Incorporation of the respective Ln³⁺ ions in nanoparticles is crucial, as controls, in which the various Ln³⁺ ions are incorporated directly into the sol-gel, that do not show cooperative up-conversion     

Saturable absorbers based on impurity and defect centers incrystals

Saturation of near-infrared absorption and transmission dynamics are investigated in tetravalent-chromium-doped Gd₃Sc₂ Ga₃O₁₂, Gd₃Sc₂Al₃ O₁₂, and Mg₂SiO₄ crystals, as well as in reduced SrTiO₃ using 20 ps 1.08 μm laser pulses. An absorption cross section of (5±0.5)×10^-18 cm² in garnets and (2.3±0.3)×10^-18 cm² in forsterite is estimated for the ³A ₂-³T₂ transition of tetrahedral Cr⁴⁺. Q-switched and ultra-short pulses are realized in neodymium lasers using chromium-doped crystals as the saturable absorbers. Saturation of free-carrier absorption with ultra-short relaxation time is observed in SrTiO₃ at 10⁸-10 ¹⁰ W/cm² pump intensities, while at 10¹⁰-10¹¹ W/cm² three-photon interband transitions predominate. The free-carrier absorption cross section is estimated to be (2.7±0.3)×10^-18 cm²     

Improved gain performance in Yb3+-sensitized Er3+-doped alumina (Al2O3) channel opticalwaveguide amplifiers

Small-signal amplification in short, Yb³⁺-sensitized, Er³⁺-doped alumina (Al₂O₃) channel optical waveguides with high Er³⁺ concentrations is analyzed. Taking into account uniform up conversion, excited state absorption (ESA) from the Er³⁺ metastable level (⁴I_13/2 ), and Yb³⁺→Er³⁺ energy transfer by cross relaxation, the obtainable gain improvements compared to Yb³⁺ -free Er³⁺-doped Al₂O₃ optical waveguides are investigated. The amplifier model is based on propagation and population rate equations and is solved numerically by combining finite elements and the Runge-Kutta algorithm. The analysis predicts that 5-cm long Yb³⁺/Er³⁺ co-doped Al₂O ₃ waveguides show 13-dB net signal gain for 100 mW pump power at λ_p=980 nm     

Ni-Cr合金钎料激光钎焊金刚石表面金属化

为了研究激光钎焊金刚石磨粒表面金属化生成物类别与形成机制, 采用第一性原理的密度泛函理论对常见碳化物进行了计算, 并采用Ni-Cr合金钎料, 借助光纤激光热源对金刚石磨粒进行了激光钎焊试验, 获得了Cr₃C₂和Cr₇C₃两种碳化物的结构和力学性能参量以及金刚石磨粒表面微结构和碳化物种类。结果表明, Cr₃C₂和Cr₇C₃两者都具有金属性, 且后者韧性更强; 激光钎焊得到的金刚石磨粒与Ni-Cr合金钎料界面冶金反应层厚度约为4μm, 金刚石磨粒表面碳化物主要为Cr₃C₂; 超声辅助激光钎焊得到的金刚石磨粒表面碳化物为Cr₃C₂和Cr₇C₃, 超声波高频振动可以促进界面反应, 进而生成含碳量低的Cr₇C₃。此研究结果对激光钎焊金刚石技术的发展具有指导意义。     

Evaluation of absorption and emission properties of Yb3+doped crystals for laser applications

The emission and absorption properties of numerous host crystals doped with Yb³⁺ ions have been studied. The hosts which have been selected include LiYF₄, LaF₃, SrF₂, BaF₂, KCaF₃, KY₃F₁₀, Rb₂NaYF₆, BaY₂ F₈, Y₂SiO₅, Y₃Al₅ O₁₂, YAlO₃, LuPO₄, Ca₅(PO₄)₃F, LiYO₂, and ScBO ₃. Spectral determinations have been made of the resonant absorption and emission cross sections between 850 and 1100 nm, and the emission decay times of the upper laser level have been measured. The emission cross sections have been evaluated using the absorption cross section and principle of reciprocity, and again using the Fuchtbauer-Ladenberg formula. Agreement between the two methods is within 20% for most materials. The results are discussed in the framework of requirements for an effective diode-pumped Yb³⁺ laser system. Ca₅(PO₄)₃F:Yb is predicted to exhibit the most useful laser properties and is expected to be far superior to Y₃Al₅O₁₂:Yb in many key microscopic parameter values     

Oxynitride gate dielectrics for p+-polysilicon gate MOSdevices

Different oxynitride gate dielectrics (NH₃-nitrided, reoxidized NH₃-nitrided, N₂-annealed NH₃-nitrided, and N₂O grown oxides) are investigated for use in p⁺-polysilicon gate MOS devices. The comparison is based on flatband voltage shift as well as decrease in inversion capacitance. Results show that NH₃-nitrided and N ₂-annealed NH₃-nitrided oxides best suppress the boron penetration and, consequently, these two undesirable effects. These findings are explained on the basis of the distribution of nitrogen in various oxynitride dielectrics     

Metal–Oxide–High-$kappa$ Dielectric–Oxide–Semiconductor (MOHOS) Capacitors and Field-Effect Transistors for Memory Applications

Metal-oxide-high-kappa dielectric-oxide-silicon capacitors and transistors are fabricated using HfO₂ and Dy₂O₃ high-kappa dielectrics as the charge storage layer. The programming speed of Al/SiO₂/Dy₂O₃/ SiO₂/Si transistor is characterized by a DeltaV _th shift of 1.0 V with a programming voltage of 12 V applied for 10 ms. As for retention properties, the Al/SiO₂/Dy₂O₃/ SiO₂/Si transistors can keep a DeltaV _th window of 0.5 V for 2 times10⁸ s. The corresponding numbers for Al/ SiO₂/HfO₂/SiO₂/Si transistors are 100 ms and 2 times10⁴ s, respectively. The better performance of the Al/SiO₂/Dy₂O₃/ SiO₂/Si transistors is attributed to the larger conduction band offset at the Dy₂O₃/SiO₂ interface.     

Reliable Low-Cost Fabrication of Low-Loss $hbox{Al}_{2}hbox{O} _{3}{:}hbox{Er}^{3+}$ Waveguides With 5.4-dB Optical Gain

A reliable and reproducible deposition process for the fabrication of Al₂O₃ waveguides with losses as low as 0.1 dB/cm has been developed. The thin films are grown at ~ 5 nm/min deposition rate and exhibit excellent thickness uniformity within 1% over 50times50 mm² area and no detectable OH^- incorporation. For applications of the Al₂O₃ films in compact, integrated optical devices, a high-quality channel waveguide fabrication process is utilized. Planar and channel propagation losses as low as 0.1 and 0.2 dB/cm, respectively, are demonstrated. For the development of active integrated optical functions, the implementation of rare-earth-ion doping is investigated by cosputtering of erbium during the Al₂O₃ layer growth. Dopant levels between 0.2-5times10²⁰ cm^-3 are studied. At Er³⁺ concentrations of interest for optical amplification, a lifetime of the ⁴I_13/2 level as long as 7 ms is measured. Gain measurements over 6.4-cm propagation length in a 700-nm-thick Al₂O₃:Er³⁺ channel waveguide result in net optical gain over a 41-nm-wide wavelength range between 1526-1567 nm with a maximum of 5.4 dB at 1533 nm.     

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     

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     

Absorption loss due to complex anions in fluorozirconate glasses

A fluorozirconate glass ZBL-3 with the molar composition 0.62 ZrF4, 0.33 BaF2, 0.05 LaF3was doped with various amounts of NaPO3, KHSO4, and also with Na2CO3, NaNO3and TiOF2. Characteristic absorption bands were observed at 2100 cm^-1and 1640 cm^-1for phosphates and 2150, 2350, and 1600 cm^-1for sulfates. The absorption resulting from 1 ppm of P is 900 dB/km at 2100 cm^-1while it is slightly lower for 1 ppm of S. Carbonates and nitrates are decomposed in the glass melt and result in a small shift of the infrared multiphonon absorption.     

Er3+-Yb3+ and Er3+ doped fiberlasers

Single-mode fiber lasers operating at ~1.57 μm are described. Output powers of >2 mW are reported for laser diode pumped operation. Direct comparison is made between fiber lasers using sensitized erbium (Er³⁺ and Yb³⁺) and erbium on its own. The performance of Er³⁺-Yb³⁺ fiber lasers is analyzed in more detail as a function of fiber length. Both CW and Q-switched operations are studied and the results obtained demonstrate that practical sources at 1.5 μm are available from diode pumped Er³⁺ -Yb³⁺ systems     

Design feasibility of a single-mode optical isolator

Isolator conditions are derived by a perturbation method for optical slab isolators in which magnetooptical crystal and anisotropic dielectric crystal films are integrated for reciprocal and non-reciprocal TE-TM mode conversion functions. The general expressions show that isolator conditions can be satisfied for any combination of wavelength, normalized frequency, waveguide thickness, and gyrotropic constant of the magnetooptical crystal by appropriate choice of the magnitude of the birefringence of the top layer film and its crystal orientation angle. Design examples of single-mode isolators with waveguide thicknesses of 4, 4.5, and 5 μm are given at 1.55 μm wavelength. It is also pointed out that isolators of the above design can be fabricated with Y3Fe5O12, Y1.5Gd1.5Fe3O12, and Tm3Fe5O12crystal films as magnetooptical materials and a solid solution of LiNbO3and LiTaO3as an anisotropic film. Tolerance in the required film thickness becomes less stringent with this design. Isolation of more than 20 dB with an insertion loss of less than 0.12 dB is feasible without any parameter adjustment, even when there is as much as a ten percent deviation in the film thickness.     

Discharging process by multiple tunnelings in thin-oxide MNOS structures

A theoretical calculation is carried out on a discharging process in thin-oxide MNOS (metal-nitride-oxide-semiconductor) structures by proposing multiple and composite tunnelings. In this analysis three tunneling processes are considered: 1) from the SiO2-Si3N4interface to the Si conduction band, 2) from the Si3N4layer to the Si conduction band (directly), and 3) from the Si3N4layer to the interface (and then to the Si conduction band). The trapped electron densities at the interface and in the Si3N4layer axe investigated analytically and numerically. It is found from the analysis that the process 3) is dominant in transferring the electrons in the Si3N4layer to the Si conduction band. Furthermore, a physical interpretation for the maximum tunneling distance obtained in the previous work is given in details.     

ISFET's using inorganic gate thin films

The characteristics of various types of ISFET's using inorganic gate films are described. The pH and pNa selectivities are investigated for SiO2, Si3N4, Al2O3, alumino-silicate, and sodium-aluminosilicate gate dielectrics. The transient response and device stability are also studied for different values of solution pH. The Al2O3gate shows a nearly ideal pH response, excellent stability, and selectivity to other cations. On the other hand, the Si3N4gate is also a good pH sensor, but it is proved by the studies of SiO2and SiOxNyfilms that the oxygen content in its surface degrades its properties as a pH sensor. Sodium-alumino-silicate, which is generally known as a material for pNa selective glass electrodes, is utilized as a gate film for the pNa ISFET. The pNa selectivity of this device is comparable to that of the conventional glass electrode. The alumino-silicate gate has also a pNa selectivity, but it is inferior to the sodium-alumino-silicate gate.     

Characteristics of room-temperature 2.3-µm laser emission from tm3+in YAG and YAlO3

The relaxation of low-lying excited states of Tm³⁺ions doped in YAG, YAlO3, and Y2O3due to photon and phonon emission is studied theoretically. Stimulated emission cross sections (integrated over frequency), fluorescence lifetimes, and radiative quantum efficiencies are calculated and their implications for laser operation on the 2.3-μm³F4→³H5line of Tm³⁺are discussed. The calculations, based on a few phenomenological parameters which have been determined by others, are easily generalizable to other host materials and other rare-earth (RE) ions. Room-temperature pulsed laser emission from Tm³⁺ions near 2.3 μm was observed on one line in Tm:Cr:YAG, and on four lines in Tm:Cr:YAlO3. Lower oscillation thresholds were generally obtained in the YAlO3 rods, consistent with the theory presented. A threshold of 31 J was obtained with a Tm:Cr:YAlO3rod at 2.274 μm. In the free-running pulsed mode, peak power levels up to several hundred watts and total output energies up to 12 mJ/pulse were observed. Other general, observed operating characteristics are discussed.     

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     

The effect of pair-induced energy transfer on the performance ofsilica waveguide amplifiers with high Er3+/Yb3+concentrations

High-concentration Er³⁺/Yb³⁺ co-doped silica waveguide amplifiers are numerically analyzed. With optimized rare-earth concentrations the effect of Er³⁺/Er³⁺ ion-pairs can be neglected and each Er³⁺ ion can be assumed to be paired only to the surrounding Yb³⁺ ions. The rate-equations model includes uniform upconversion mechanisms from ⁴I_13/2 and ⁴I_11/2 erbium levels and an Yb³⁺ to Er³⁺ pair-induced energy transfer process. Numerical results demonstrate the possibility of fabricating short- and high-gain integrated optical amplifiers; it is shown that net gain as high as 3 dB/cm can be obtained     

7B4--Absorption and emission properties of optically pumped ruby

Several experiments on optically excited ruby are described. First, absorption transitions initiated from the metastable states,tmin{2}max{3}²Eandtmin{2}max{3}²T1, are investigated in the photon energy range from 5500 to 45 000 cm^-1. The absorption spectrum of these excited states is determined in bothpi-and σ-polarizations and assignments for the observed absorption bands are achieved. Obtained results are compared with other experiments reported in the literature. Next, emission properties of pink ruby are studied in the region near theRlines. The emission spectrum is determined point by point by means of intense flash excitation. The observed weak bands are ascribed to theR'and phonon assistedRtransitions. Laser actions in these bands are discussed and experimental results on phonon terminated laser amplification are presented. An experiment using a giant pulse as an excitation source reveals that the transition time fromtmin{2}max{3}²Etotmin{2}max{3}²T1is shorter than a fraction of 1μs at room temperature.