An optically pumped supersonic iodine beam laser

We report the realisation of an optically pumped I₂-laser using a supersonic beam as active medium. Threshold pump power of the order of 10 mW and output power at λ_d=1.34 μm of up to 2 mW is observed with λ_p=514.5 nm as pump radiation. In contrast to the similar Na₂-beam laser, the output of a ring cavity is bidirectional with a forward to backward intensity ratio of about 10:1.     

New phenomena related to pulsed far-infrared superradiant and Raman emissions

We report on new effects in relation to optical pumping of far-infrared (FIR) superradiance and Raman emissions in CH₃F, CH₃CN, D₂O, NH₃ by rapidly truncated 10 μm CO₂ laser pulses and optical-free-induction decay (OFID) 30 ps-10μm-CO₂ laser pulses. Thus, we have found a drastic reduction of the FIR-pulse duration which is closely related to the fast truncation of about 10 ps of the plasma shutter used in our OFID 10 μm-CO₂ laser system. The forward emissions exhibit the on-set of swept-gain superradiance and the appearance of Raman emission with increasing pressure in the FIR cell. This implies line competition between the superradiant and Raman emissions and thus results in different emission regimes which we have investigated systematically. The backward emissions are superradiant over the whole range of our investigations and show high quality with respect to stability and reproducibility which is important for applications.Furthermore, we have found that the CO₂-pump radiation and the generated FIR Raman emission interact mutually which results in anticorrelated fluctuations of the two fields. We have been able to interpret this effect as a result of periodic back-and-forth fluctuations of the Λ-like three-level molecular systems.Finally, we have observed the development of OFID of the truncated CO₂-pump pulses in the FIR-laser gases. This effect has been thoroughly investigated and as a result we have generated for the first time ps-10 μm-CO₂-OFID pulses with FIR-laser gases as spectral filters instead of the usual hot CO₂ gas. New phenomena and advantages of our new OFID system based on FIR laser gases are discussed.     

Simultaneous dual-wavelength operation at 1.06 and 1.34 μm in Nd-vanadate laser crystals

Output performances of Nd-vanadate lasers with simultaneous dual-wavelength emission on the 1.06-μm ⁴ F _3/2 → ⁴ I _11/2 transition and the ⁴ F _3/2 → ⁴ I _13/2 transition at 1.34 μm are discussed. The design uses a linear resonator for emission at 1.06 μm and an L-type folded resonator for the 1.34-μm wavelength, and the ratio between the power of a single wavelength and the total power is adjusted by the choice of the output mirror transmissions. A continuous-wave (CW) Nd:GdVO₄ laser with total output power in the range of 3.9 to 6.8 W and the corresponding ratio of the output power at 1.06 μm to the total output power between 0.26 and 0.97 is realized. It is also shown that in comparison with the pump at 808 nm, the pump directly into the ⁴ F _3/2 emitting level at 879 nm improves the total output power. Furthermore, a Nd:GdVO₄ laser with simultaneous emission at 1.06 and 1.34 μm and that generates also green light at 0.53 μm by intracavity frequency-doubling with LiB₃O₅ (LBO) nonlinear crystal is demonstrated.     

Dual-wavelength stimulated emission from a double-layer Cd x Hg1 − x Te structure at wavelengths of 2 and 3 μm

Dual-wavelength stimulated emission from a double-layer Cd _x Hg_{1 ? x} Te heterostructure optically pumped by a pulsed Nd:YAG laser at temperatures T = 77–150 K is reported. The emission spectral lines have been observed at wavelengths λ₁ ～ 2 μm and λ₂ ～ 3 μm. Emission spectra recorded at different temperatures are presented.     

Tm3+/Ho3+共掺碲酸盐玻璃的2.0μm发光特性及能量传递

研究了Tm³⁺/Ho³⁺共掺TeO₂-WO₃-ZnO玻璃在808 nm激光二极管抽运下的2.0μm发光特性及Tm³+与Ho³⁺之间的能量传递.应用Judd-Ofelt理论计算了Ho³⁺在碲酸盐玻璃中的谱线强度参量Ω_t (t=2,4,6)、自发辐射概率A_r、辐射寿命τ_r等.计算了Ho³⁺的吸收截面σ_a(λ)和受激发射截面σ_e(λ).结果表明：碲酸盐玻璃中Tm³⁺→Ho³⁺正向能量传递系数大约是Tm³⁺←Ho³⁺反向能量传递系数的18倍.Ho³⁺离子的⁵I₇能级的寿命为3.9ms，2.0μm处的最大发射截面为9.15×10^-21cm².在0.5mol% Tm₂O₃和0.15mol% Ho₂O₃共掺的碲酸盐玻璃中能获得2.0μm的最大增益.通过比较氟化物、碲酸盐和镓铋酸盐重金属氧化物等玻璃中Ho³⁺的量子效率η，σ_e×τ_m值和增益系数G(λ)等，发现Tm³⁺/Ho³⁺共掺碲酸盐玻璃是一种理想的2.0μm激光器用基质玻璃. 关键词： 2.0μm发光 能量传递 增益 碲酸盐玻璃     

Direct observation of Raman shifts in a fir superradiant laser

Fabry-Perot frequency measurements of FIR superradiant emission from D₂O at 99 μm are reported. Several Fabry-Perot scans at different frequency settings of the CO₂ pump laser show a shift in the FIR output spectrum equal, within experimental error, to the shift in input frequency of the CO₂ pump. The “superradiant” emission therefore of the D₂O 10_1,10(010) → 9_0,9(010) transition at 99 μm contains a strong Raman component.     

Polarization enhancement of anti-Stokes emission in a para-H2 Raman laser

The effect of polarization can influence the frequency conversion and enhance the anti-Stokes emission in a rotational para-H₂ Raman laser. Stokes (16 μm) and anti-Stokes (7 μm) radiations were obtained from a line tunable CO₂ laser at 10 μm.     

CW infrared laseraction of optically pumped Co2+:KZnF3

The optical properties of KZnF₃:Co²⁺ were investigated by means of absorption and emission spectroscopy in the visible and infrared spectral region. This system is suitable for laseraction between the lowest ⁴T₁(⁴F)-⁴T₂(⁴F) Co²⁺ phonon sidebands. CW laseraction of more than 20 mW (85K) was observed at 1.95 μm when pumped with an Ar⁺-laser at 514 μm (1.5W). The system is at least tunable between 2.05 μm to 1.85 μm.     

Intense 2.7 µm emission and structural origin in Er³⁺-doped bismuthate (Bi₂O₃-GeO₂-Ga₂O₃-Na₂O) glass

The 2.7 μm emission properties in Er³⁺-doped bismuthate (Bi₂O₃-GeO₂-Ga₂O₃-Na₂O) glass were investigated in the present Letter. An intense 2.7 μm emission in Er³⁺-doped bismuthate glass was observed. It is found that Er³⁺-doped bismuthate glass possesses high spontaneous transition probability A (65.26 s^-1) and large 2.7 μm emission cross section σ_em (9.53×10^-21?cm²) corresponding to the stimulated emission of Er³⁺:⁴I_11/2→⁴I_13/2 transition. The emission characteristic and energy transfer process upon excitation of a conventional 980 nm laser diode in bismuthate glass were analyzed. Additionally, the structure of bismuthate glass was analyzed by the Raman spectrum. The advantageous spectroscopic characteristics of Er³⁺ single-doped bismuthate glass together with the prominent thermal property indicate that bismuthate glass might become an attractive host for developing solid-state lasers around 2.7 μm.     

Wave mixing and amplified spontaneous emission in pure potassium and mixed sodium-potassium vapors

We report observations of several wave-mixing and stimulated processes in pure potassium and mixed sodium-potassium vapors which are excited by a pulsed laser operating in the range 680–800 nm. When the laser is tuned to the potassium two-photon 4S6S transition, we observe stimulated emission on the various cascade transitions as well as four- and six-wave mixing. When the laser is tuned over the range 747 to 753 nm, which is well away from all atomic transitions, we observe strong forward and weak backward emission at the potassium 3D _3/24P _1/2 transition wavelength (1.17 m). However, this latter emission is only observed in the mixed sodium-potassium vapor. We present data on the excitation spectrum, forward to backward asymmetry, temporal dependence, and the laser power dependence of this emission. We speculate that twophoton photodissociation of the NaK molecule is responsible for this emission.     

New FIR laser lines from an optically pumped far-infrared laser with isotopic 13C16O2 pumping

A ¹³C¹⁶O₂ laser optically pumping a FIR laser has resulted in 17 new FIR cw emissions from 78.5 μm to 917 μm. The FIR media were: CD₃OD, CH₃OD, CD₃OH, NH₃ and ¹⁵NH₃. Interesting effects have been observed with a combination of NH₃ and CD₃OD resulting in a new FIR emission. Two new FIR emissions at 181.5 μm and 355.5 μm have been observed with a ¹²C¹⁶O₂ laser optically pumping CD₃OD.     

Fabrication and characterization of transparent Tm,Ho:YAG ceramic

Transparent Tm,Ho:YAG ceramic with excellent optical properties was fabricated by solid-state reaction method using high-purity commercial powders as raw materials. Optical absorption and 2.0 μm emission spectra of the ceramic specimen have been studied. The strongest emission corresponds to ⁵ I ₇ → ⁵ I ₈ transition of Ho³⁺ centered at 2.06 μm. As a result, Tm,Ho:YAG ceramic shows potential application in 2.0 μm laser devices.     

Origin of backward to forward wave dominance in broadband Raman scattering in hydrogen

We have observed that in a multilens H₂ cell it is possible to obtain a total dominance of the first Stokes backscattered wave with respect to the forward wave [1]. This dominance of the backward wave is produced by a combination of a strong focusing and a matched backward mode stimulated by the forward generation. A quantitative analysis of the backward gain and of the forward gain suppression due to the interference with a matched antiStokes generation is performed. Both the gain and bandwidth analysis are in agreement with a theory of multimode broadband scattering in quasi-stationary regime. A matched backward mode is observed for the pump and its mixing with the first Stokes backward emission induces weak high order backward Raman generations that should be in principle not observable.     

Stimulated Raman conversion of radiation from a YAG:Nd laser with wavelengths of 1.319, 1.338, and 1.357 µm in a barium nitrate crystal

We have studied stimulated Raman (SRS) conversion to the first Stokes component of multimode (M₂ = 8) radiation from a YAG:Nd laser with lasing wavelengths of 1.319 μm, 1.338 μm, and 1.357 μm in a barium nitrate crystal. We have obtained pulses of converted radiation with energies up to 120 mJ. We have achieved conversion efficiencies greater than 40% for each of the three Raman laser wavelengths of 1.530 μm, 1.556 μm, and 1.582 μm with divergence of the beams of converted radiation close to the diffraction-limited value (M₂ < 1.5). __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 3, pp. 330–334, May–June, 2006.     

Non-collinear phase matched 4-wave mixing of CO2 and NH3 laser radiation in germanium

4-wave mixing has been demonstrated in room temperature germanium using a TEA CO₂ laser (9.3 μm) and an optically pumped NH₃ laser (12.8 μm) as radiation sources. Non-collinear phase matched emission near 7 μm has been observed with a mixing efficiency close to the calculated value. The extension of this mixing process to generate wavelengths in the important region near 16 μm is discussed.     

Ultrashort 1.5-microm laser excited upconverted stimulated emission based on simultaneous three-photon absorption

Simultaneous three-photon excited stimulated emission at (cavityless lasing) approximately 610 nm has been achieved in an organic chromophore solution pumped by approximately 1.5-microm ultrashort coherent radiation. The stimulated emission can be observed only in the forward and backward directions and is characterized by its high directionality and spectral narrowing. The divergence angle for the backward stimulated emission is considerably smaller than that for the forward stimulated emission, which resembles optical phase conjugation.     

Mid-Infrared Emission Characteristic and Energy Transfer of Ho<Superscript>3+</Superscript>-Doped Tellurite Glass Sensitized by Tm<Superscript>3+</Superscript>

We report on 2.0-μm emission characteristic and energy transfer of Ho³⁺-doped tellurite glass sensitized by Tm³⁺ upon excitation of a conventional 808 nm laser diode. The Judd-Ofelt strength parameters, spontaneous radiative transition probabilities and radiative lifetime of Ho³⁺ have been calculated from the absorption spectra by using the Judd-Ofelt theory. Significant enhancement of 2.0-μm emission of Ho³⁺ has been observed with increasing Tm³⁺ doping up to 0.7 mol%. The energy transfer coefficient of the forward Tm³⁺→Ho³⁺ is approximately 17 times larger than that of the backward Tm³⁺←Ho³⁺ energy transfer. Our result indicates that the maximum gain of 2.0-μm emission, assigned to the transition of ⁵I₇→⁵I₈ of Ho³⁺, might be achieved from the tellurite glass at the concentration of 0.5 mol% of Tm₂O₃ and 0.15 mol% of Ho₂O₃. The high gain coefficient and quantum efficiency (1.16) along with the large value of the product of the stimulated emission cross-section and the measured radiative lifetime (4.12×10⁻²⁷ m²s) of the Ho³⁺/Tm³⁺-codoped tellurite glasses might find potential applications in efficient 2.0-μm laser.     

混合形成体对掺铒碲酸盐玻璃的热力学稳定性和发光性能的影响

研究了混合形成体效应对掺铒碲酸盐玻璃热力学稳定性、1.53 μm发光特性和上转换发光强度的影响.通过拉曼光谱测试,分析了WO₃,Nb₂O₅,GeO₂等氧化物对Er³⁺离子配位场结构,以及对发光谱的非均匀展宽机理的作用.结果表明,通过掺杂适当声子能量的网络形成体氧化物,不但可获得热力学稳定性较好的玻璃,还可有效降低Er³⁺离子⁴I_11/2能级的寿命,在抑制Er³⁺离子在可见光波段的上转换发光的同时不致劣化其在1.53 μm的发光特性.本文制得的碲酸盐玻璃具有较大的受激发射截面((9.64—10.96)×10^-21cm²)和荧光半高宽(FWHM)(50—67 nm),热力学稳定性良好,是一种理想的掺Er³⁺宽带有源光纤用基质玻璃. 关键词： 掺铒碲酸盐玻璃 混合形成体 1.53 μm发光 声子能量     

Single-mode optical pumping and superradiant emission in D2O and CH3F

Superradiant FIR emission in both D₂O and CH₃F has been investigated using a tunable single-mode CO₂ TEA laser as optical pump, and results compared with multimode pumping. The frequency offset of the absorbing transitions has been measured and compared to other work. Estimates of the dipole transition moments were also obtained from saturation broadening data. Fine structure of the CH₃F (Q12, K) lines have been resolved and compared with theory. High quantum conversion efficiencies were observed for several lines in D₂O: 38% (99 μm), 20% (385 μm) and 12.5% (121 μm) and in CH₃F 21% (496 μm).     

Photoluminescence of cis- and trans-polyacetylene

The emission intensity in cis-(CH)_χ increases a little and the emission peak shifts a little to shorter wavelength with increasing temperature, which can be interpreted by the distribution of several emission centers in energy. Photoluminescence is also observed in trans-(CH)_χ at around 1.03 μm for the first time.