Er3+掺杂新型GeS2-In2S3-CsI玻璃上转换光谱性质研究

用熔融淬冷法制备了掺Er³⁺的80GeS₂-10In2S₃-10CsI(mol%)硫卤玻璃样品,测试了样品的热学稳定性、喇曼光谱、吸收光谱以及上转换光谱,分析了Er³⁺离子在该玻璃中的上转换发光机理.应用Judd-Ofelt理论计算分析了Er3+离子在该样品中的强度参量Ωt(t=2,4,6)、自发辐射跃迁几率A、荧光分支比β以及辐射寿命τrad等光谱参量.在980 nm LD泵浦激发下,首次在该种玻璃中观察到强烈的绿光(526 nm、549 nm),分别对应于2H11/2→4I15/2和4S3/2→4I15/2的跃迁,其中549 nm处绿光较强.549 nm处上转换荧光寿命为0.34 ms,量子效率为69%.同时研究了绿光(526 nm、549 nm)上转换发光强度随泵浦激发功率的变化,其发光曲线拟合斜率分别为1.71和2.03,表明绿光是双光子吸收过程.研究结果表明：掺Er³⁺的80GeS₂-10In2S₃-10CsI硫卤玻璃是一种上转换绿光激光器的潜在基质材料.     

Multiple-wavelength lasing by multiform self-frequency conversion in Nd<Superscript>3+</Superscript>-doped La<Subscript>2</Subscript>CaB<Subscript>10</Subscript>O<Subscript>19</Subscript> crystals

The self-sum-frequency process was firstly demonstrated in Nd³⁺-doped La₂CaB₁₀O₁₉ (LCB) crystal. In addition, simultaneous participation of the fundamental laser in multi-self-frequency conversion including the self-frequency doubling was reported. Emissions at five different wavelengths (525, 529, 533.6, 1050 and 1069 nm) were simultaneously obtained. The output power of the three green visible lasers (525, 529 and 533.6 nm) generated by multi-self-frequency-conversion of the fundamental laser is up to 26.64 mW, and the light-light conversion efficiency is up to 4.85%. The lasers at 525 and 529 nm are very close to the green primary color G (526.3 nm) defined by the 1964CIERGB system, which has potential applications in laser-based high brightness display. The large frequency differences of 4–6 THz between 525 and 529 nm, 529 and 533.6 nm, as well as 1050 and 1069 nm, are also potential useful in generating THz waves by difference frequency generation (DFG) technique in a nonlinear optical (NLO) crystal.     

Diode-pumped Nd:YVO4 laser emitting at 1074 nm based on the 4F3/2-4I11/2 transition

We report a diode-pumped Nd:YVO₄ laser emitting at 1074 nm, based on the ⁴ F _3/2-⁴ I _11/2 transition, generally used for a 1064 nm emission. A power of 323 mW at 1074 nm has been achieved in continuouswave (CW) operation with a fiber-coupled laser diode emitting 18.2 W at 808 nm. Intracavity second-harmonic generation in CW mode has also been demonstrated with a power of 18 mW at 537 nm by using a LiB₃O₅ (LBO) nonlinear crystal.     

Efficient fourth harmonic UV generation of passively Q-switched Nd:GdVO4/Cr:YAG lasers

A coherent UV passively Q-switched diode pumped Nd:GdVO₄ laser source is proposed. During pumping of the β-BBO crystal a stable light with power 0.6 W with wavelength 532 nm and pulse duration 9 ns at frequency repetition 16 kHz was applied. The output UV light has a power about 79 mW at wavelength 266 nm during diode-pumping with 8 W incident light.     

Analysis of the nuclear quadrupole interaction of Disulfur Dichloride, S2Cl2

Pure rotational spectra of S₂³⁵Cl₂ and S₂³⁵Cl³⁷Cl have been observed using a Fourier-transform microwave spectrometer. An analysis of the hyperfine structure made by considering the nuclear spin statistics showed that S₂Cl₂ has C₂symmetry, where the hyperfine splittings due to the two Cl nuclei were analyzed precisely. The nuclear quadrupole coupling constants including the off-diagonal (χ_ab, χ_ac, χ_bc) components and the nuclear spin–rotation interaction constants associated with the two Cl nuclei have been determined for the first time. We have shown that the nuclear quadrupole interaction plays an important role in the ortho–para mixing.     

Tunable frequency-controlled laser source in the near ultraviolet based on doubling of a semiconductor diode laser

Continuously tunable ultraviolet laser radiation at 397 nm was generated by doubling the output of a semiconductor diode laser. The fundamental radiation was provided by a 150 mW AlGaAs laser diode injected by a low-power AlGaAs laser diode which was frequency stabilized by optical feedback using a new scheme of a miniature external cavity. Second-harmonic generation was produced in a lithium-triborate crystal placed in a compact enhancement cavity. The fundamental radiation was used for sub-Doppler spectroscopy of the Ar I 4s ³ P ⁰ ₀–4p ¹ P ₁ transition at 795 nm; the second-harmonic radiation was used for spectroscopy of the Ca II 4² S _1/2–4² P _1/2 transition at 397 nm.     

Diode laser measurements of line strengths and collisional half-widths in thev2band of14NH3 and15NH3

A tunable diode laser spectrometer was used to perform measurements of half-widths and intensities of several rotational lines in v₂-band of ammonia. The intensity measurements of 16 lines of¹⁵NH₃ allowed us to estimate v₂-band strength of this molecule at 298 K to be S_v ⁰=(550±10) cm^–2-atm^–1.     

Study on nonlinear optical absorption properties of [(CH3)4N]2[Cu(dmit)2] by Z-scan technique

The third-order optical nonlinearities of an organo-metallic compound, [(CH₃)₄N]₂[Cu(dmit)₂] (dmit²⁻=4,5-dithiolate-1,3-dithiole-2-thione), abbreviated as MeCu, dissolved in acetone are characterized by Z-scan technique with picosecond and nanosecond laser pulses in the near-infrared region. Two-photon absorption has been found when the sample solution is irradiated by 40 ps pulse width at 1064 nm and the two-photon absorption (TPA) coefficient β_TPA is 4×10⁻¹³ m/W. While excited by 15 ns laser pulses at 1053 nm, the Z-scan spectra reveal strong reverse saturable absorption (RSA) and the nonlinear absorption coefficient β_RSA is estimated to be as high as 7.07×10⁻¹¹ m/W which is much larger than β_TPA. An explanation for this enhancement is given. All the results suggest that MeCu may be a promising candidate for the application to optical limiting in the near-infrared region.     

Spectral characterization and energy levels of Cr:Sc2(MoO4)3 crystal

This paper reports the spectral properties and energy levels of Cr³⁺:Sc₂(MoO₄)₃ crystal. The crystal field strength Dq, Racah parameter B and C were calculated to be 1408 cm⁻¹, 608 cm⁻¹ and 3054 cm⁻¹, respectively. The absorption cross sections σ_α of ⁴A₂→⁴T₁ and ⁴A₂→⁴T₂ transitions were 3.74×10⁻¹⁹ cm² at 499 nm and 3.21×10⁻¹⁹ cm² at 710 nm, respectively. The emission cross section σ_e was 375×10⁻²⁰ cm² at 880 nm. Cr³⁺:Sc₂(MoO₄)₃ crystal has a broad emission band with a broad FWHM of 176 nm (2179 cm⁻¹). Therefore, Cr³⁺:Sc₂(MoO₄)₃ crystal may be regarded as a potential tunable laser gain medium.     

Diode-pumped continuous-wave Nd:YAP laser emitting at 1073 nm based on the 4F3/2-4I11/2 transition

We describe the output performances of the 1073 nm ⁴ F _3/2 → ⁴ I _11/2 transition (generally used for a 1064 nm transition) in Nd³⁺:YAlO₃ (Nd:YAP) under in-band pumping with diode laser at the 803 nm wavelength. An end-pumped Nd:YAP crystal yielded 390 mW of continuous-wave (CW) output power for 17.8 W of incident pump power. Moreover, intracavity second-harmonic generation has also been achieved with a power of 38 mW at 536 nm by using a LiB₃O₅ (LBO) nonlinear crystal. The green beam quality factor M ² was less than 1.33. The blue power stability was less 3.5% in 4 h.     

Frequency measurement of I2 lines in the NIR using Ca and CH4 optical frequency standards

2 lines have been carried out using difference-frequency mixing of the emission of CH₄ and Ca frequency standards at 88 THz (or 3.4 μm) and 456 THz (or 657 nm), respectively. A power of ≈10 pW for the mixing product at 815 nm was obtained using a critically phase-matched KTP crystal and input powers of the order of mW. The relative uncertainty of the measurement was a few times 10^-11, limited by the frequency instability of the laser source locked to I₂. Received: 3 December 1997/Revised version: 16 February 1998     

The T1←S0 Absorption Spectrum of Gaseous 4H-Pyran-4-thione

The T₁←S₀ absorption spectrum of 4H-pyran-4-thione (PT) was measured in a static cell at room temperature (550-620 nm) and in a seeded cold supersonic jet (580-600 nm) using the cavity ring-down (CRD) method. In the static cell absolute extinction coefficients were determined between 573 and 610 nm with an accuracy of ∼±5%. In this region 22 harmonic sequences and 18 hot bands were observed. The energetically lowest ground state vibration at 167.5 cm⁻¹ was identified as the promoting mode in the static PT gas. The mode in the triplet state was found at 152.3 cm⁻¹. The CRD absorption spectra of static PT gas and jet-cooled PT are compared with the phosphorescence excitation spectrum of isolated PT. The weak S_{1, 0}←S_{0, 0} absorption was tentatively assigned to a transition at ∼17433 cm⁻¹.     

A high-stability semiconductor laser system for a <Superscript>88</Superscript>Sr-based optical lattice clock

We describe a frequency-stabilized diode laser at 698 nm used for high-resolution spectroscopy of the ¹S₀–³P₀ strontium clock transition. For the laser stabilization we use state-of-the-art symmetrically suspended optical cavities optimized for very low thermal noise at room temperature. Two-stage frequency stabilization to high-finesse optical cavities results in measured laser frequency noise about a factor of three above the cavity thermal noise between 2 Hz and 11 Hz. With this system, we demonstrate high-resolution remote spectroscopy on the ⁸⁸Sr clock transition by transferring the laser output over a phase noise-compensated 200-m-long fiber link between two separated laboratories. Our dedicated fiber link ensures a transfer of the optical carrier with frequency stability of 7×10⁻¹⁸ after 100 s integration time, which could enable the observation of the strontium clock transition with an atomic Q of 10¹⁴. Furthermore, with an eye toward the development of transportable optical clocks, we investigate how the complete laser system (laser+optics+cavity) can be influenced by environmental disturbances in terms of both short- and long-term frequency stability.     

Photoacoustic detection of oxygen using cantilever enhanced technique

A tunable diode laser photoacoustic setup based on a recently demonstrated cantilever technique was used for sensitive detection of oxygen. As light sources, we used a distributed feedback (DFB) diode laser and a vertical-cavity surface-emitting (VCSEL) laser, both operating near 760 nm. With the 30 mW DFB laser a noise-equivalent detection limit of 20 ppm for oxygen was obtained, while a detection limit of 5 ‰ was achieved with the VCSEL having an output power of 0.5 mW. Our results yield a noise-equivalent sensitivity of 4.8×10^-9 cm^-1W Hz^-1/2 and demonstrate the potential of this technique for compact and sensitive measurement of oxygen. PACS 42.62.Fi; 42.55.Px; 82.80.Kq     

Violet light generation by frequency doubling of GaAlAs diode laser using a metallo-organic complex crystal ZnCd(SCN)4

Violet 404-nm radiation is generated by type-I single-pass frequency doubling of the output of an GaAlAs diode laser in critically phase-matched ZnCd(SCN)₄ (ZCTC) crystal, a metallo-organic complex crystal. In this paper, its refractive index and second-harmonic generation phase-matching angles are reported. Using a 3-mm-long ZCTC crystal, a diode laser power of 473 mW generated 390 μW of second-harmonic radiation. More recently, 380-nm, 20 μW ultraviolet (UV) radiation is also realized by frequency doubling of the 100 mW output of a continuous-wave Ti:sapphire laser at 760 nm. ZCTC is a promising UV nonlinear optical candidate material for frequency doubling of diode lasers.     

Visible-to-near infrared standard source generation using acetylene (C2H2)-stabilized comb-injection-locked technique

An ultra-stable visible laser source (VLS) was generated by the second harmonic of a selectively injection-locked distributed feedback (DFB) laser from an optical frequency comb with acetylene-stabilized laser seeding. For the second-harmonic generation (SHG) of the injection-locked DFB laser, we used periodically poled lithium niobate (PPLN) crystal and generated the VLS at a region of 771 nm, which was discretely locked to a spacing of 25 GHz within the PPLN bandwidth (180 GHz). The frequency stability of this source was estimated to be 1.1 × 10^− 12 with an average time of 1 s.     

Continuous wave laser operation of Yb<Superscript>3+</Superscript>:YVO<Subscript>4</Subscript>

We have demonstrated the continuous wave laser operation of Yb³⁺:YVO₄. For Ti:Al₂O₃ laser pumping at 985 nm, a maximum slope efficiency of 41.1% and a threshold pump power of 76 mW were obtained. The maximum output power was 433 mW at a laser wavelength of 1037 nm.Using a cw diode laser around 974 nm as a pump source, a slope efficiency of 10.9% and a maximum output power of 152 mW were achieved at a laser wavelength of 1039 nm. The laser threshold pump power was 608 mW with respect to the absorbed pump power. The effective emission cross-sections for the ²F_5/2²F_7/2 transition were determined using the Füchtbauer–Ladenburg equation. The maxima of the effective absorption and emission cross-sections were found at 984.5 nm (6.74×10^-20 cm²) in -po larization and 985.5 nm (4.28×10^-20 cm²) also in -p olarization. The upper laser level lifetime was measured with suppression of radiation trapping and is around 318 s. PACS 42.55.Rz; 42.55.Xi; 42.70.Hj     

805-nm diode-pumped continuous-wave 2-µm laser performance of Tm3+:BaGd2(MoO4)4 cleavage plate

End-pumped by a single-stripe 805-nm diode laser, a maximum continuous-wave output power of 290 mW with slope efficiency of 42% and 90 mW with slope efficiency of 44% around 2 μm were achieved in a 1.6-mm-thickness, unprocessed 7.2 at.% Tm³⁺:BaGd₂(MoO₄)₄ cleavage plate in a hemispherical and plano–plano cavities, respectively, when the absorbed pump power was 830 mW. The dependence of the polarization of output laser on the output coupler transmission was investigated. The influence of upconversion on the laser performance was analyzed. The results show that the unprocessed Tm³⁺:BaGd₂(MoO₄)₄ cleavage plate is a promising 2-μm laser gain medium pumped by diode laser around 808 nm.     

Observation and optimization of DAVLL spectra on the S0-P1 transition of neutral mercury atom

The dichroic atomic vapor laser locking (DAVLL) spectra on the ¹S₀-³P₁ transition of neutral mercury atoms are reported for the first time. Two classes of DAVLL line shapes corresponding to single resonant transition and the combinations of several transitions are experimentally observed and compared with numerical simulation. The dependences of peak-to-peak amplitude and the slope near the zero-crossing point on the axial magnetic field and cell temperature are also investigated. A simple model was introduced to briefly estimate the optimal magnetic field with the largest slope. The optimal operating parameters in a 1 mm cell are highlighted to use DAVLL to lock the frequency of the 253.7 nm UV trap laser of mercury atoms.     

Ultrahigh-resolution laser spectroscopy of the S1B2u ← S0Ag transition of perylene

A rotationally resolved ultrahigh-resolution fluorescence excitation spectrum of the S₁ ← S₀ transition of perylene has been observed using a collimated supersonic jet technique in conjunction with a single-mode UV laser. We assigned 1568 rotational lines of the band, and accurately determined the rotational constants. The obtained value of inertial defect was positive, accordingly, the perylene molecule is considered to be planar with D_2h symmetry. We determined the geometrical structure in the S₀ state by ab initio theoretical calculation at the RHF/6-311+G(d,p) level, which yielded rotational constant values approximately identical to those obtained experimentally. Zeeman broadening of each rotational line with the external magnetic field was negligibly small, and the mixing with the triplet state was shown to be very small. This evidence indicates that intersystem crossing (ISC) in the S₁¹B_2u state is very slow. The rate of internal conversion (IC) is also inferred to be small because the fluorescence quantum yield is high. The rotational constants of the S₁¹B_2u state were very similar to those of the S₀¹A_g state. The slow internal conversion (IC) at the S₁ zero-vibrational level is attributed to a small structural change upon electronic transition.