Optical amplification of argon excimers in the vacuum ultraviolet spectral region, produced by ultrashort-pulse high-intensity-laser-produced electrons

Optical-field-induced ionization (OFI) electrons were produced in a 30 cm Ar-filled hollow fiber by shining a high-intensity laser into the fiber. By use of such a long plasma with the help of a multilayer dielectric mirror made for 126 nm emission, we observed significant optical amplification of the Ar₂ ^* emission at 126 nm. The optical amplification resulted in a maximum small signal gain coefficient of 0.16 cm^-1 at 126 nm at 10 atm of Ar pressure.     

Production of laser-heated plasma in high- pressure Ar gas and emission characteristics of vacuum ultraviolet radiation from Ar2 excimers

A new pump scheme for the realization of a practical Ar₂ excimer laser operating at 126 nm has been proposed and investigated experimentally. In this scheme, pre-ionized high-pressure Ar gas was excited by an intense transversely-excited atmospheric (TEA) CO₂ laser irradiation. A 100-mm-long line plasma was successfully produced at an argon gas pressure of 2 MPa. The vacuum ultraviolet emission at 126 nm from the Ar₂ excimers was observed and its emission characteristics were investigated under various experimental conditions. Received: 10 December 2001 / Published online: 14 March 2002     

Improved gain for the Ar 2 * excimer laser at 126 nm

Argon was excited by intense electron beam pumping. The optical gain obtainable in Ar ₂ ^2* at 126 nm was investigated as a function of gas pressure and pumping density. The gas pressure necessary to achieve a gain of 10%/cm is reduced from 3.2 to 1.0 MPa if the gas is cooled at 170 K. The effect is partly due to reduced absorption by the removal of impurities. The results allow one a new approach to construct high-power lasers in the vacuum ultraviolet below 150 nm.     

1150 nm High-Power Fiber Laser Oscillator Pumped by 976 nm Laser Diode

We present an all-fiber 1150 nm Yb-doped fiber laser oscillator pumped by a 976 nm laser diode. To suppress amplified spontaneous emission and avoid parasitic laser oscillation, we propose a long-length gain fiber and a high-reflectivity output fiber Bragg grating in the fiber laser oscillator. The 1150 nm band single-mode fiber laser with output power of 20.5 W is demonstrated at room temperature. The optical-to-optical conversion efficiency ranges up to 51.6% at the maximum output. The central wavelength of the fiber laser oscillator is 1150.35 nm, and its 3 dB spectral width is 0.72 nm. No evidence of amplified spontaneous emission, residual pump light, or parasitic laser oscillation were observed in the experiments. The high-power 1150 nm fiber laser oscillator can be used as a pump source in the development of a 3 μm Ho-doped fiber laser.     

毛细管放电类氖氩69.8nm激光增益特性研究

建立了计算69.8nm激光增益系数的理论模型,根据实验参数,计算了在主脉冲电流为12 kA时,69.8nm激光增益系数最大值为0.32 cm~(-1).理论模拟了不同初始气压下增益系数在毛细管径向上的分布情况.对理论结果的分析表明,最佳的初始气压在12—14 Pa范围内,此时69.8nm激光增益系数的极值最大.实验上,利用毛细管放电装置和罗兰光谱仪,测量了不同气压下的69.8nm激光强度,实验确定的最佳气压为16 Pa,与理论结果相近.此外,实验测量的增益系数(0.4 cm~(-1))略高于理论计算的增益系数(0.32 cm~(-1)).     

High upconversion optical gain of Er3+-doped tellurite glass

The upconversion technique of rare-earth-doped glasses or crystals is a potential route for achieving short-wavelength lasers (SWLs). The optical gain is an important parameter for evaluating lasing medium performance. Therefore, upconversion luminescence in glass with composition of 70TeO₂–9PbF₂–10AlF₃–10BaF₂–1Er₂O₃ was demonstrated, and the small-signal optical gain was measured via an amplified spontaneous emission technique when the sample was excited with a 980 nm laser. It was found that the optical gain was as large as 4.0 dB/cm, thus indicating that this glass may be a good medium for SWLs.     

基于双程放大的毛细管放电69.8 nm激光增益特性

建立了类氖氩C线69.8 nm激光的双程放大实验后反射腔结构,利用45 cm长毛细管作为放电负载得到了其双程放大输出.在相同初始实验条件下,分别测量了单程放大输出与双程放大输出的激光脉冲光强、脉冲宽度以及激光束散角.通过对比单程与双程输出实验结果,利用双程放大激光光强的计算公式,分析得到了增益持续时间大于4 ns,以及增益在毛细管径向上的分布特点.以上结果为建立谐振腔进行毛细管放电类氖氩激光的多程放大实验奠定了基础.     

High-gain amplification in Yb:CaF2 crystals pumped by a high-brightness Yb-doped 976 nm fiber laser

We report on high single-pass gain in Yb:CaF₂ crystal longitudinally pumped with a 40 W high-brightness fiber laser source based on an ytterbium-doped ultra-large core photonic crystal rod-type fiber operating at 976 nm. A single-pass small-signal gain of 3.2 has been achieved in a 6 % Yb-doped 10-mm-long CaF₂ crystal at room temperature, outperforming any CW-diode-pumped scheme and paving the way towards very promising innovative lasers and amplifiers schemes merging the Yb-doped solid-state and fiber technologies.     

Fluoride glass Raman fiber laser at 2185 nm

We report on the first Raman laser based on a fluoride glass optical fiber. The Raman fiber laser was pumped by a 9.6?WTm3+:silica CW fiber laser operating at a wavelength of 1940?nm. A maximum output power of 580?mW was measured at 2185.1?nm, corresponding to a frequency shift of 579?cm(-1) (17.37?THz). We observed a threshold power of 3.8?W and a low power slope efficiency of 29% with respect to the launched pump power. Using those results and the known fiber parameters, we estimated a Raman gain peak value of 3.52*10(-14)?m/W, which is lower than the previously reported values.     

Observation of vacuum-ultraviolet Kr(2)* laser oscillation pumped by a compact discharge device

We have demonstrated vacuum-ultraviolet (VUV) Kr(2) * laser oscillation as a result of the realization of a stable self-sustained discharge of high-pressure Kr by use of a compact discharge device. Glow discharge was obtained with as much as 10 atm of pure Kr. The VUV emission intensity centered at 147.8 nm abruptly increased when the charging voltage exceeded a certain value. In addition to this threshold behavior, considerable spectral narrowing (4.0?0.4 nm) was observed when the charging voltage increased. The maximum output energy at 148 nm was 150muJ . The gain coefficient was estimated to be 1.1% cm (-1) .     

Output power improvement in an Yb-doped fiber laser with an additional unpumped Yb-doped fiber

Master oscillator power amplifier (MOPA) technology has been widely used in high-power or ultrashort-pulse fiber laser systems because the shape of the laser pulse can be easily adjusted. Usually, the first amplification stage of a 1064 nm fiber laser uses the core-pumped Yb-doped fiber amplifier (YDFA); however, the gain or output power is limited owing to the strong amplifier spontaneous emission (ASE) in the 1030 nm band. This paper presents the improved output power in an YDFA by inserting an additional unpumped Yb-doped fiber, which absorbs the lost backward ASE emitted from the pump end. We achieved an output power increase of more than 10% in a low-power signal, and the increase in output power decreased as the signal power increased. Moreover, the insertion of an additional unpumped Yb-doped fiber restricted the unwanted 1030 nm lasing in a low-power signal.     

Mode-locked fiber laser in the C-band region for dual-wavelength ultrashort pulses emission using a carbon nanotube saturable absorber

A saturable absorber is commonly employed to generate an ultrashort laser with a mode-locking scheme. In an erbium-doped fiber laser system, the laser regimes of either 1530 or 1550 nm wavelength are procured based on the absorption profile of the erbium-doped fiber. The absorption of the erbium-doped fiber is designed to emit at both wavelengths by controlling the net gain of the laser cavity. Subsequently, simultaneous erbium-doped fiber laser emission is attained at 1533.5 and 1555.1 nm with the pulse duration of 910 and 850 fs, respectively.Therefore, this work maximizes the output portfolios of a mode-locking fiber laser for dual-wavelength ultrashort pulses emission.     

Development of ultra-short pulse VUV laser system for nanoscale processing

We have developed intense vacuum ultraviolet (VUV) radiation sources for advanced material processing, such as photochemical surface reactions and precise processing on a nanometer scale. We have constructed a new VUV laser system to generate sub-picosecond pulses at the wavelength of 126 nm. A seed VUV pulse was generated in Xe as the 7th harmonic of a 882-nm Ti:sapphire laser. The optimum conversion was achieved at the pressure of 1.2 Torr. The seed pulse will be amplified by the Ar₂^*\mathrm{Ar}_{2}^{*} media generated by an optical-field-induced ionization Ar plasma produced by the Ti:sapphire laser. We have obtained a gain coefficient of g=0.16 cm⁻¹. Our developing system will provide VUV ultra-short pulses with sub-μJ energy at a repetition rate of 1 kHz.     

掺钕保偏光纤放大器的研究

对掺钕双包层光纤放大器中抽运光和信号光沿光纤传播的功率分布进行了数值模拟,以808nm半导体激光器为抽运源,掺钕双包层保偏光纤为增益介质,对种子注入主振荡光纤放大器进行了理论分析和实验研究.利用实验室自制的皮秒锁模激光器为种子源,注入1064nm皮秒锁模脉冲,获得了稳定的放大脉冲.小信号时的放大倍数为300（增益为25dB）,获得了平均功率5W的皮秒脉冲.同时利用TDS5104型示波器探测信号光放大前后的波形,并用光谱分析仪得到输出脉冲激光的光谱图. 关键词： 光纤放大器 掺钕保偏光纤 种子注入 反向抽运     

基于增益光纤长度优化的双波长运转掺铒光纤锁模激光器

构建了可自启动的双波长运转掺铒光纤锁模激光器.通过优化增益光纤长度,利用掺铒光纤在1530nm附近的再吸收效应调节激光器的增益谱,使激光器在1530nm和1560nm附近具有相同的增益强度.实验中采用31cm掺铒光纤作为增益光纤,以透射式半导体可饱和吸收体作为锁模器件,实现了自启动双波长锁模运转.激光器锁模输出重复频率为58.01MHz,信噪比为58.2dB,最高输出功率为4.8mW.锁模输出的光谱在1532.4nm和1552.3nm处具有两个强度接近的谱峰,谱峰间距约为20nm.该激光器无需手动调节即可实现双波长运转,更便于实际使用.     

Measurement of electronegativity during the E to H mode transition in a radio frequency inductively coupled Ar/O_2 plasma

This paper presents the evolution of the electronegativity with the applied power during the E to H mode transition in a radio frequency(rf)inductively coupled plasma(ICP)in a mixture of Ar and O2.The densities of the negative ion and the electron,as well as their ratio,i.e.,the electronegativity,are measured as a function of the applied power by laser photo-detachment combined with a microwave resonance probe,under different pressures and O2 contents.Meanwhile,the optical emission intensities at Ar 750.4 nm and O 844.6 nm are monitored via a spectrograph.It was found that by increasing the applied power,the electron density and the optical emission intensity show a similar trench,i.e.,they increase abruptly at a threshold power,suggesting that the E to H mode transition occurs.With the increase of the pressure,the negative ion density presents opposite trends in the E-mode and the H-mode,which is related to the difference of the electron density and energy for the two modes.The emission intensities of Ar 750.4 nm and O 844.6 nm monotonously decrease with increasing the pressure or the O2 content,indicating that the density of high-energy electrons,which can excite atoms,is monotonically decreased.This leads to an increase of the negative ion density in the H-mode with increasing the pressure.Besides,as the applied power is increased,the electronegativity shows an abrupt drop during the E-to H-mode transition.     

Highly efficient 4-W Yb-doped fiber amplifier pumped by a broad-stripe laser diode

A Yb-doped double-cladding fiber amplifier is v-groove side pumped by a 100-mum -wide, broad-stripe, 975-nm laser diode. The amplifier exhibits, separately, 39% electrical-to-optical conversion efficiency, 89% internal optical-to-optical conversion efficiency, 4-W output power at 1060 nm, and a small-signal gain of 53 dB.     

Erbium-ytterbium co-doped multi-wavelength double-clad fiber laser around 1612 nm

We report an erbium-ytterbium (Er/Yb) co-doped multi-wavelength laser operation around 1612 nm. The fiber laser was constructed in a figure-of-eight configuration and using a piece of polarization-maintaining (PM) Er/Yb double clad fiber as the gain medium. The oscillation laser lines around 1612 nm could be controlled by carefully adjusting the polarization controllers in the cavity, which might result in single line, dual line or triple line fiber laser operation. The line space was measured about 3.3 nm (±0.2 nm) which was believed to be strongly dependent on the length of the PM Er/Yb co-doped double-clad fiber.     

High-power tunable diode-pumped Yb3+:CaF2 laser

Results of diode-pumped cw laser operation of an Yb3+:CaF2 single crystal are reported for what is to our knowledge the first time. With a 5-at.% Yb3+ -doped sample we obtained 5.8-W output power at 1053 nm for 15 W of incident power at 980 nm. The laser wavelength could be tuned from 1018 to 1072 nm, and a small-signal gain as high as 1.8 was achieved, showing the great potential of Yb3+:CaF2 as an amplifier medium for femtosecond pulses.     

Diagnostics of the inductively coupled plasma by diode laser absorption spectroscopy

A vertical-cavity surface-emitting diode laser is used as a tunable emission source to measure the radius-integrated gas temperature in an inductively coupled plasma reactor. Relevant data are obtained by profiling the Doppler-broadened absorption of metastable Ar atoms at 763.51 nm in argon and argon-nitrogen (3, 45, and 90% N₂ in Ar) plasmas in the pressure range 0.5–70.0 Pa and at an inductive power of 100 and 300 W. The results are compared with the rotational temperature of molecular nitrogen. The difference between the integrated rotational and Doppler temperatures is attributed to the nonuniform spatial distributions of the temperature and thermometric atomic and molecular species (Ar* and N*₂). These distributions are computed in terms of the nonequilibrium hydrodynamic model of plasma. The objective of this work is to develop a contactless (nonintrusive) technique for measuring the temperature and concentration of different particles in the reactor with a microsensor.