Excited-state absorption cross sections in the 800-nm band for Er-doped, Al/P-silica fibers: Measurements and amplifier modeling

Excited-state absorption (ESA) cross sections were determined for the 800-nm band of Er-doped, Al/P-silica fibers. The oscillator strength of the ESA transition exceeds that of the 800 nm, ground-state absorption (GSA) transition by a factor of approximately= 2.3, in reasonable agreement with a Judd-Ofelt calculation. The extended, long-wavelength tail of the GSA band leads to a region around 820 nm where the GSA cross section approximately= ESA cross section. The cross sections were incorporated into an amplifier model for pumping in the 800-nm band. Codirectional and the bidirectional pumping schemes were analyzed for excitation near the peak and in the long wavelength tail of the GSA band. Pumping in the tail for either pumping scheme or pumping near the peak for the bidirectional scheme are predicted to produce a significant improvement in the small-signal gain.<>     

Multiphoton‐Pumped Highly Polarized Polariton Microlasers from Single Crystals of a Dye‐Coordinated Metal–Organic Framework

Room‐temperature, low‐threshold, photostable, cost‐effective, efficient, miniaturized, and all‐solid‐state lasers are highly desirable in many technological and medicinal applications. Here, an archetypical dye laser is introduced, with the above attributes, based on single‐crystalline microplates of a dye‐coordinated metal–organic framework (MOF) without an external cavity, holding a potential to be the next‐generation laser. With an exciton–polariton lasing mechanism combined with large multiphoton absorption cross sections, the lasing thresholds of the three microplates are in the range from 0.34 to 0.12 µJ cm^?2 under various optical pumping schemes. The lasing threshold is observed to be reduced with an increment in the order of optical nonlinearity involved in the pumping scheme. Lasing at an extreme‐red region is demonstrated, with a high photostability (with a drop in lasing output as low as 25% after 1.8 × 10⁶ cycles), a large degree of polarization (up to 92%), and an excellent conversion efficiency (up to 12%), thereby realizing a crucial milestone in the field of laser technology.     

激光功率密度对低浓度若丹明6G染料激射寿命的影响

把固体染料激光器工作介质激射寿命的概念推广到液体染料激光器中,同时提出了一种针对液体激光染料激射寿命的双激光光路测试方法.该方法使用波长为532 nm的Nd:YAG脉冲激光器作为抽运光来模拟染料激光器中的抽运条件,用波长相同的低功率连续激光作为监测染料分子在抽运光作用下失效速率的手段.利用半导体制冷器件,PID温控仪和水浴槽实现了液体染料的恒温控制.测量了激光平均功率密度从6.3×103～2.2×104 W/m2变化范围内R6G染料乙醇溶液的激射寿命.实验结果表明,染料的激射寿命与抽运光功率密度成反比,比例系数可以解释为染料分解一半时,分子单位吸收截面上累积的辐照能量.用该系数表征染料的激射寿命特征更具有普遍意义.     

Wavelength selection and tuning by optical control in a two-segmenterbium-doped fiber laser

A new method for controlling the wavelength of an Er³⁺-doped fiber laser is proposed and demonstrated. Using two sections of dissimilar Er³⁺-doped fiber and pumping them separately, switching among several distinct lasing wavelengths has been observed. Wavelength tuning over a range of 8 nm has also been achieved     

Properties of two-photon pumped cavity lasing in novel dye dopedsolid matrices

Two-photon pumped frequency upconversion cavity lasing at ~600 nm is accomplished in three types of dye-doped solid rods pumped with ~10 ns and 1.06-μm IR laser pulses. The dopant is a new dye, trans-4-[p-(N-ethyl-N-(hydroxyethyl)amino)styryl]-N-methylpyridinium tetraphenylborate, abbreviated as ASPT, which possesses a greater two-photon absorption cross section and stronger upconversion fluorescence emission than common commercial dyes (such as rhodamine). Three different materials were chosen as solid matrices: poly(2-hydroxyethyl methacrylate), VYCOR porous glass, and sol-gel glass. Using a Q-switched Nd:YAG pulse laser as the pump source, strong cavity lasing could be achieved in these three ASPT doped solid rods as well as in ASPT solution in a liquid cell. The spectral, temporal, and spatial characteristics of the cavity lasing output have been systematically investigated. The measured output-input characteristics, lasing lifetime, and damage threshold for the three different rods are presented     

Practical aspects of lasing without inversion in various media

A rigorous density-matrix-based theory of lasing based on optically induced or autoionization-induced coherence between the levels is developed. The balance equations are obtained, and the conditions for lasing threshold are derived as a function of pumping strength and relaxation rates. Connection between the lasing without inversion and Raman and parametric processes is established. The main conclusion is that true CW lasing without inversion can indeed be obtained but only in a system where pumping and relaxation rates are favorable for attaining conventional lasing with population inversion. Practical implications of it, especially for the intersubband lasers, are discussed     

Spectra of the lowest excited singlet states of rhodamine 6G and rhodamine B

Excited states of laser dyes were generated in solution by an intense 6 ns laser pump pulse tuned to the absorption maximum of the longest wavelength, ground state absorption band. They were interrogated by a shorter, simultaneous, monochromatic pulse of smaller diameter, concentric and collinear with the pump, having a crossed polarization. Plots of transmission curves against intensity for the pump beams approached residual absorptions at the highest intensities. Gain or attenuation of the probe was measured throughout the region of the long wavelength absorption bands, at the 578.2 nm copper vapor laser wavelength, and for rhodamine 6G across the lasing band. Gains were determined at different probe intensities, and were extrapolated to small-signal values. The dyes have fluorescences at the ground state absorption maxima, hence pumping at these wavelengths cannot achieve 100 percent S1population. Auxiliary saturation transmissions were determined beyond the fluorescence bands and the first experiments were corrected to give a measure ofsigma_{e} - sigma^{ast}, the difference between the stimulated emission cross section and the excited state absorption cross section. Assumptions in the experiment and improvements in experimental technique are discussed.     

Materials for a Reliable Solid‐State Dye Laser at the Red Spectral Edge

In the search to extend the tuning range of solid‐state dye lasers (SSDLs) to the red‐edge spectral region, new photosensitive materials have been designed and synthesized based on six commercial dyes (sulforhodamine B, perylene red, rhodamine 640, LDS698, LDS722, and LDS730) incorporated into different linear, crosslinked, fluorinated, and sililated polymeric matrices. Under transversal pumping at 532 nm, these materials exhibit highly efficient, stable, as well as wavelength‐tunable laser action from the visible‐to‐NIR spectral region (575–750 nm). The lasing performance of the materials doped with perylene and xanthene dyes is, to the best of our knowledge, the highest achieved to date for these chromophores when incorporated into organic, inorganic, or hybrid matrices. Regarding the LDS derivatives, this is the first time that laser action from these dyes in solid‐state media is reported. These particular characteristics have impelled the building of the first prototype SSDL that is compact, versatile, and easy to handle.     

Determination of interface trap capture cross sections usingthree-level charge pumping

A modified three-voltage-level charge pumping (CP) technique is described for measuring interface trap parameters in MOSFETs. Charge pumping (CP) is a technique for studying traps at the Si-SiO₂ interface in MOS transistors. In the CP technique, a pulse is applied to the gate of the MOSFET which alternately fills the traps with electrons and holes, thereby causing a recombination current I_cp to flow in the substrate. With this technique, interface trap capture cross sections for both electrons and holes may be determined as a function of trap energy in a single device. It is demonstrated that a modified three-level charge pumping method may be used to determine not only interface trap densities but also to capture cross sections as a function of trap energy. The trap parameters are obtained for both electrons and holes using a single MOSFET     

980 nm抽运时掺铒光纤放大器中的上转换发光效应研究

采用980nm抽运的掺铒光纤放大器（EDFA）中存在上转换发光效应。能级分析和光谱扫描结果表明上转换辐射光为绿色荧光。波长为538nm和514nm，其产生机理为铒离子的激发态吸收效应（ESA）。从理论和实验两方面分析了抽运功率和信号功率这两个放大参量对上转换绿色荧光的影响，结果表明，存在一个特殊抽运功率值，当抽运功率小于该值时，上转换绿色荧光的抽运效率随抽运功率的增加而快速增大；抽运功率大于该值时，上转换绿色荧光的抽运效率变化缓慢，基本保持稳定。掺铒光纤放大器工作在线性放大状态下，输入信号的有无和功率大小对绿色荧光影响很小；掺铒光纤放大器工作在饱和状态下，绿色荧光功率随输入信号功率增加而增加。     

Excited-state-absorption cross sections and amplifier modeling inthe 1300-nm region for Nd-doped glasses

The performance of Nd³⁺-doped fibre amplifiers is limited by strong excited-state absorption (ESA) of the signal, and, even for fluorozirconate glasses, ESA prevents the important region below 1320 nm from being used. To quantify this limitation and explore alternative host materials, ESA and stimulated-emission cross sections have been measured for a representative group of glass compositions. These parameters have been used in an accurate fiber-amplifier model to provide the first quantitative comparisons of performance for Nd³⁺ -doped glasses in the 1300-nm band as a function of host     

Characterization of radiative and nonradiative Processes in Nd:YAG lasers by comparing direct and band pumping

Heat generation and laser performance of Nd:YAG oscillators pumped in two regimes, band pumping at /spl sim/808 nm and "thermally boosted" (TB) pumping at 884.5 nm, are compared. The crystal, pumped with a Ti:sapphire laser, lased with slope efficiencies of 52% and 57% when pumped at 802 and 884.5 nm, respectively. The heat generated during lasing was found to be 27% lower with TB pumping as compared to traditional band pumping. Moreover, the experimental results suggest that the coupling efficiency between the pump band and the upper lasing level (the quantum efficiency) is unity, and about 8% of the upper lasing level population decays via nonradiative channels.     

Small-signal gain measurement in a Ti:Al2O3amplifier

A small-signal single-pass power gain of e^5.2=180 has been measured for a signal in the π polarization at 790.7 nm in a longitudinally pumped Ti:Al₂O ₃ amplifier. A double-pass power gain of e^5.2 ≈10⁴ has been attained for the same polarization at 799.8 nm. The ratio of the gain cross sections at 632.8 and 790.7 nm is 1/25. The gain anisotropy at 632.8 nm is g_π/g _σ=2.3. The lifetime of the upper lasing level decreases with increased pumping, probably as the result of amplified spontaneous emission     

Evaluation of the 800 nm pump band for erbium-doped fiberamplifiers

Performs a comprehensive experimental and theoretical investigation of methods for overcoming the excited-state absorption (ESA), which is the main obstacle to efficient pumping of erbium-doped fiber amplifiers (EDFAs) at 800 nm. The effects of ESA on gain can be reduced at the cost of an additional noise penalty by adopting bidirectional pumping or by pumping in the long-wavelength tail of the ground-state absorption (GSA) band. The GSA and ESA cross-section spectra on the glass host material. One of the most promising hosts, fluorophosphate, is compared to Al/P silica in a detailed analysis based on a quantitative numerical model. It is predicted that 2-3 dB less pump power is required for the fluorophosphate EDFA. For Al/P-silica EDFAs, it is found that ~7-dB-higher power is required when pumping in the 800 nm band than for pumping at 980 and 1480 nm     

不同波长泵浦的掺铒Al2O3薄膜光波导1．53μm荧光特性

本文通过分析饵的能级结构,考虑了合作上转换、激发态吸收及交叉驰豫等上转换机制,给出了掺铒（Er^3 )Al2O3薄膜光波导1480nm、80nm和820nm3种泵浦波长下的速率方程,通过求稳态解,分析了3种波长泵浦时发射的1．53μm荧光特性以及合作上转换和激光态吸收对荧光的影响,结果表明利用980nm波长泵浦时可得到相对较强的1．53μm荧光,产浦强度时激发态吸收对荧光影响较大,而在高掺（Er^3 ）浓度时合作上转换占主导地位。     

An analysis of cleaved coupled-cavity lasers

We present an analysis of (GaAl)As cleaved coupled-cavity (C³) lasers incorporating gain dependence on pumping and wavelength of both laser segments as well as the effects of spontaneous emission in the lasing diode section and the known dependence of file refractive index on carrier density. Our model allows us to analyze the physical origin of the experimentally observed variations in the lasing longitudinal mode number with the modulator laser section current. It also indicates a strong dependence of device behavior on the gap length and yields precise variations in threshold current with modulator current. In addition, the model predicts that in the vicinity of particular current values large (∼ 100 Å) wavelength shifts can be observed. These shifts could be useful in optical fiber communications multiplexing applications. Finally, results for C³lasers with sections of quite dissimilar length are presented and we note that these devices exhibit more erratic behavior than the lasers with sections of comparable length.     

Maximum performance of discharge-pumped exciplex laser atλ=222 nm

The results of an experimental investigation into lasing and spontaneous emission from Ne(He, Ar)-Kr-HCl are presented. Evidence has been gathered of the effect of the pumping power, preionization rate, pumping pulse duration, and composition and pressure of the gas mixture on the lasing characteristics under discharge pumping. KrCl* formation efficiency is shown to be nearly half as much as for XeCl*. The output energy was 0.65 J for ~60 ns laser pulse duration (FWHM), 2.5% efficiency based on the pumping power, and 0.65% efficiency based on the stored energy while for the 10 ns pulse duration, 2.7% efficiency based on the pumping power and 0.8% efficiency based on the stored energy the output energy was 0.15 J. Recommendations are made for development of KrCl lasers with maximum output parameters     

Theoretical modeling of optical amplification in Er-doped Ti:LiNbO3 waveguides

An accurate theoretical analysis is presented describing optical amplification in Er-diffused Ti:LiNbO₃ channel waveguides. It follows as far as possible the theory already developed for Er-doped fibers. As optical pumping around λ_p≈1.48 μm is considered, a quasi-two-level model for the Er³⁺ ions is used with wavelength-dependent cross sections. The optical gain in the 1.53 μm<λ<1.64-μm wavelength range is evaluated. The characteristic parameters, as Er concentration profile, cross sections, pump, and signal mode distributions and waveguide (scattering) losses are taken from experiments. Examples of numerically calculated pump-, small-signal-gain-, and ASE-evolutions are presented. The model has been tested by comparing computed and experimentally observed gain characteristics for Xˆ- and Yˆ-cut LiNbO₃; an almost quantitative agreement has been obtained     

A new simplified charge pumping current model and its modelparameter extraction [MOSFET]

Using the Shockley-Read-Hall (SRH) theory, a simple analytic charge pumping current model has been developed and its accuracy verified by exact numerical analysis. It is shown that the derived analytic charge pumping current model with constant capture cross sections for electrons and holes does not correctly simulate the rising (falling) edges of the experimental charge pumping current. According to the slopes of the logarithmic charge pumping current, effective capture-cross-section models for elections and holes are proposed and are incorporated into the developed analytic charge pumping current model. It is shown that the experimental charge pumping current can be simulated very well by using the modified analytic model     

Wavelength tuning of the stimulated emission from GaAs and CdSe electron-beam-pumped lasers

The wavelength at which the stimulated output from a number of electron-beam-pumped semiconductor lasers peaks is a function of the time after the start of the pumping pulse. In general, the output intensity reaches a maximum at short wavelengths considerably before it peaks at the longest. Detailed observations of the wavelength shifts of the peak output as a function of both time and pumping current are reported here for both CdSe and GaAs laser crystals. It is found that the rate of shifting of the wavelength peak (tuning rate) as a function of electron-beam pumping current is very similar in both functional form and magnitude in the two materials. Furthermore, the behavior of the tuning rate is dependent on whether or not lasing action occurs in the crystal under examination. For a crystal in which lasing action is obtained, the tuning rate saturates for pumping current densities above threshold. In contrast, for a nonlasing crystal, the tuning rate is a linearly increasing function of the pumping current density. The implications of these results are discussed with reference to previously reported work concerning shifts with respect to the band edge of the stimulated emission from semiconductor lasers.