Diode laser overtone spectroscopy of CO2 at 780 nm

Overtone absorption lines of ¹²C¹⁶O₂ have been examined by using a tunable diode laser (TDL) spectrometer in the region around . The spectrometer sources are commercially available double heterostructure InGaAlAs TDLs operating in the “free-running” mode, which allowed the detection of the line positions within . The observed carbon dioxide absorption lines belong to the ν₁+5ν₃ ro-vibrational band with rotational quantum number J up to 48. The minimum absorbance detected by the spectrometer (?5×10^-6) permitted to observe the weakest lines having the absorption cross section of the order of .     

Diode laser spectroscopy of CO2 at 790 nm

Absorption lines of ¹²C¹⁶O₂ have been examined by using a tunable diode laser spectrometer in the region around (790 nm). The spectrometer sources are commercially available double heterostructure InGaAlAs tunable diode lasers (TDLs) operating in the “free-running” mode, which allowed the detection of the line positions within . The observed carbon dioxide absorption lines belong to the combination overtone 2ν₂+5ν₃ ro-vibrational band with intensities ranging around .     

Diode laser spectroscopy of ethylene overtones at 830 nm

A tunable diode laser spectrometer has been employed to examine the 3rd overtone absorption lines of C₂H₄ at around 12 000 cm⁻¹ (830 nm). The spectrometer sources are heterostructure AlGaAs tunable diode lasers operating “free-running”. By the aid of the wavelength modulation spectroscopy with the second harmonic detection technique and a Herriott type multipass cell 63 very weak absorption lines have been observed for the first time, with cross sections as low as 2 × 10⁻²⁶ cm²/mol, equivalent to . The self-broadening coefficient has been measured for one of the most intense lines.     

Self-broadening coefficients in the ν4 band of CH4 by diode-laser spectroscopy

With a diode-laser spectrometer, we have measured self-broadening coefficients of 42 lines of the P-, Q- and R-branches in the ν₄ fundamental band of CH₄ at room temperature, with J values ranging between 1 and 12. For the determination of self-broadening parameters, we have fitted to the experimental lineshape two theoretical line profiles: the Voigt profile taking into account Doppler and collisional broadenings, and the hard collision model developed by Rautian and Sobel’man incorporating Dicke narrowing.     

Diode-laser spectroscopy: Temperature dependence of R (0) line in the ν4 band of CH4 perturbed by N2 and O2

In this paper, we present a line profile study of the R (0) line in the ν₄ band of methane diluted in nitrogen and oxygen, from room temperature to 153 K. The measurements were performed over a total pressure range from 14 to 128 mbar. The collisional broadening and narrowing (Dicke effect) coefficients are derived from a fit of the experimental spectra by using the soft and hard collision models, taking into account the Dicke effect. For higher pressures, we have fitted the data with a model taking into account simultaneously the Dicke narrowing and the speed dependence effect. Finally, we have deduced the parameter n of the temperature dependence (inverse power law) of the broadening coefficients for the CH₄-N₂ and CH₄-O₂ gas mixtures.     

Diode laser spectroscopy of ammonia at 760 nm

A tunable diode laser spectrometer has been employed to examine the unknown overtone absorption lines of NH₃ around (760 nm). The spectrometer sources are commercially available heterostructure AlGaAs tunable diode lasers operating in the “free-running” mode. The detection of the lines has been possible by the use of the wavelength modulation spectroscopy and the second harmonic detection technique. A special algorithm has been used in order to fit the highly modulated absorption lines. The weakest observed resonances have absorption cross sections on the order of ?/molecule or ?/amagat. For some of the more intense lines self-, air-, N₂-, He- and H₂-broadening coefficients have been obtained at room temperature and also some shifting coefficients have been measured.     

Line profile study by diode laser spectroscopy in the CH4ν2 + ν4 band

We present a complete study on four methane lines for two atmospheric micro-windows (in the ν₂ + ν₄ absorption band) used for the determination of atmospheric methane concentrations with ground-based Fourier transform spectrometers. Thanks to our tunable diode laser (TDL) spectrometer with active wavenumber control and step-by-step recording mode we have improved the accuracy on intensity, broadening, narrowing, and pressure shift parameters. To make our results directly useable in atmospheric models which usually assume a Voigt line shape, we have parameterised an effective-broadening parameter γ_Voigt (P) for each line and each gas mixture (CH₄-N₂ and CH₄-O₂). When this parameterisation is used to fit a “true” line profile, the same concentration as with more sophisticated models is retrieved using a consistent set of spectroscopic parameters in both approaches.     

Pulsed Nd:YAP laser at 1432 nm pumped with high power laser diode

LD end pumped Nd:YAP laser operation in the eye safe spectrum region at 1432 nm is reported. With pump energy of 256 mJ, maximum linearly polarized output of 26 mJ is obtained. The optical-to-optical overall efficiency is around 10%, and the slope efficiency is around 18%. The laser beam operates with spiking mode with a total emission period of less than 300 µs at 10 Hz. The stimulated emission cross section is estimated at around 0.85 × 10^− 20 cm².     

Efficient Tm, Ho-co-doped silica fibre laser diode pumped at 1150 nm

High power and highly efficient operation of a Tm³⁺, Ho³⁺-doped silica fibre laser that is pumped with diode lasers operating at 1150 nm is demonstrated. Internal slope efficiencies approaching the Stokes limit were produced and the maximum output power was 2.9 W. High power diode lasers operating at 1150 nm are valuable pump sources for a range of fibre lasers offering output in the shortwave infrared spectrum.     

Highly efficient Nd:GdVO4/BiBO laser at 456 nm under direct 880 nm diode laser pumping

The continuous-wave high-efficiency laser emission of Nd:GdVO₄ at the second-harmonic of 456 nm obtained by intracavity frequency doubling with an BiB₃O₆(BiBO) nonlinear crystal is investigated under pumping by diode laser at 880 nm into emitting level ⁴F_3/2. About 3.8 W at 456 nm with M² = 1.4 was obtained from a 5 mm-thick 0.4 at.% Nd:GdVO₄ laser medium and a 12 mm-long BiBO nonlinear crystal in a Z-type cavity for 13.9 W absorbed pump power. An optical-to-optical efficiency with respect to the absorbed pump power was 0.274. Comparative results obtained for the pump with diode laser at 808 nm, into the highly-absorbing ⁴F_5/2 level, are given in order to prove the advantages of the 880 nm wavelength pumping.     

High-efficiency Nd:GdVO4 laser at 1341 nm under 880 nm diode laser pumping into the emitting level

Highly efficient 1341 nm continuous-wave laser under 880 nm diode laser pumping in Nd:GdVO₄ crystal is reported. Comparative results obtained by the traditional pumping at 808 nm were presented, showing that the slope efficiency and the threshold with respect to the absorbed pump power under 880 nm pumping was 34.9% higher and 12.6% lower than those of 808 nm pumping. A high slope efficiency of 49.1% was achieved under 880 nm pumping, with an optical-to-optical conversion efficiency of 41.7%.     

Spectral line parameters in the (4 ← 0) overtone band and the dipole moment function of HI

We present new measurements of the line strengths in the third vibrational overtone band in pure HI and its mixtures with Ne, Ar, and Xe, and report results of the Herman-Wallis analysis for this band. Significance of the higher-order terms in the polynomial representation of the dipole moment function is discussed. It is concluded that the spectroscopic data yield the dipole moment function fully described by a cubic polynomial in powers of the reduced displacement from the equilibrium bond length. In the Padé approximant for the dipole moment function, the vicinity of the saddle point near equilibrium also can be accurately fitted with a cubic polynomial. Pressure line broadening and shifting parameters are reported for mixtures of HI with rare gases.     

Comparison of 885 nm pumping and 808 nm pumping in Nd:CNGG laser operating at 1061 nm and 935 nm

A Nd:CNGG laser operated at 935 nm and 1061 nm pumped at 885 nm and 808 nm, respectively, is demonstrated. The 885 nm direct pumping scheme shows some advantages over the 808 nm traditional pumping scheme. It includes higher slope efficiency, lower threshold, and better beam quality at high output power. With the direct pumping, the slope efficiency increases by 43% and the threshold decreases by 10% compared with traditional pumping in the Nd:CNGG laser operated at 935 nm. When the Nd:CNGG laser operates at 1061 nm, the direct pumping increases the slope efficiency by 14% with a 20% reduction in the oscillation threshold.     

An 8.1 W diode pumped solid-state quasi-continuous-wave yellow laser at 589 nm by intracavity sum-frequency mixing generation

We report an L-shaped symmetrical co-folding-arm plane-plane diode pumped solid-state yellow laser at 589 nm by using intracavity sum-frequency mixing. By carefully designing the cavity and employing various techniques to optimize the laser’s specifications, a quasi-continuous-wave (QCW) free-oscillation yellow laser source, which has an average output power of 8.1 W, a beam quality factor of M² = 2.3, and a repetition rate of 1.1 kHz, is developed. The generation of yellow laser at 589 nm is achieved by intracavity sum-frequency mixing between the laser lines at 1319 nm and 1064 nm of an Nd:YAG laser in a KTP crystal. To the best of our knowledge, the 8.1 W output at 589 nm is higher than any other diode pumped solid-state yellow laser generated by intracavity sum-frequency generation so far.     

The v6 = 1 and v6 = 2 vibrational states of DCF3

The high-resolution infrared spectra of DCF₃ were reinvestigated in the ν₆ fundamental band region near 500 cm⁻¹ and around 1000 cm⁻¹ with the aim to assign and analyze the overtone level of the asymmetric CF₃ bending vibration v₆ = 2.The present paper reports on the first study of both its sublevels (A₁ and E corresponding to l = 0 and ±2, respectively) through the high-resolution analysis of the overtone band and the hot and bands.The well-known “loop method”, applied to and , yielded ground state energy differences Δ(K, J) = E₀(K, J) − E₀(K − 3,J) for the range of K = 6 to 30.In the final fitting of molecular parameters, we used the strategy of fitting all upper state data together with the ground state rotational transitions.This is equivalent to that calculating separately the and coefficients of the K-dependent part of the ground state energy terms from the combination loops.All rotational constants of the ground state up to sextic order could be refined in the calculation.This led to a very accurate determination of C₀ = 0.18924413(25) cm⁻¹, , and also .In the course of analyzing simultaneously the overtone band together with the and ν₆ bands, the original assignment of the fundamental ν₆ band [Bürger et al., J. Mol. Spectrosc. 182 (1997) 34-49] was found to be incompatible with the present one. Assignments of the (k + 1, l₆ = +1)/(k − 1,l₆ = −1) levels had to be interchanged, which changed the value of Cζ₆ = −0.14198768(26) cm⁻¹ and the sign of the combination of constants C − B − Cζ in the v₆ = 1 level to a negative value.     

可调谐半导体激光吸收光谱监测农田气体通量特性研究

可调谐半导体激光吸收光谱(TDLAS)具有高选择性,高灵敏度等特性,非常适合监测农田痕量气体交换过程。采用开放式光程的可调半导体激光吸收光谱和非分散红外光谱技术,在封丘农田进行了一个月监测试验。选择CO2作为目标气体,用两种不同光谱技术选择不同的通量计算方法,分别获取农田排放通量。根据实验条件,提出了TDLAS的通量印痕模型,对比分析了两种技术的空间代表性特性,同时分析了数据误差来源和不同外界因素对通量测量的影响特性。结果发现在相同的气象条件下,仪器架设高度越高,光学路径越长,开放光路的TDLAS通量贡献区就越大。这些结果对通量监测中仪器安装有很好的指导意义。     

Absorption and luminescence spectroscopy of fused silica by multiple pulses irradiation at 355 nm

In this work, the effects of laser irradiation on fused silica at 355 nm are investigated by using transient absorption spectroscopy and luminescence spectroscopy. Our result shows that no transient absorption or luminescence in the spectra range from 400 nm to 600 nm is observed when laser energy density is below the damage threshold. When the laser energy density reaches the threshold, an initial damage site will be created. After subsequent laser pulses irradiation, the damage size grows. At the same time, the intensity of the transient absorption and luminescence spectra at the damage site also raises remarkably with the laser pulse number increasing. The absorption band from 420 nm to 520 nm is probably related to the absorption of impurity such as metal ion of iron, cerium and copper. Laser modified fused silica exhibits intense broad luminescence bands due to oxygen-deficiency centers at 444 nm and 580 nm.     

Efficient quasi-three-level Nd:YAG laser at 946 nm pumped by a tunable external cavity tapered diode laser

Using a tunable external cavity tapered diode laser (ECDL) pumped quasi-three-level Nd:YAG laser, a fivefold reduction in threshold and twofold increase in slope efficiency is demonstrated when compared to a traditional broad area diode laser pump source. A TEM₀₀ power of 800 mW with 65% slope efficiency is obtained, the highest reported TEM₀₀ power from any 946 nm Nd:YAG laser pumped by a single emitter diode laser pump source. A quantum efficiency of 0.85 has been estimated from experimental data using a simple quasi-three-level model. The reported value is in good agreement with published values, suggesting that the model is adequate. Improvement of the 946 nm laser due to the ECDL's narrow spectrum proves to be less significant when compared to its spatial quality, inferring a broad spectrum tapered diode laser pump source may be most practical. Experimental confirmation of such setup is given.     

High-resolution diode laser absorption spectroscopy of the O-H stretch overtone band (2,0,0)←(0,0,0) of the HO2 radical

The O-H stretching overtone (2ν₁) of the HO₂ radical was observed between 6603.2 to by using tunable diode laser absorption spectroscopy (TDLAS). About 1000 lines were observed in this region of which 491 transitions could be definitively assigned to the 2ν₁. The spectrum is observed to be an A/B hybrid band with band features of both a perpendicular and parallel nature. Transitions of the A-type bands with K_a^′=0-3, N^′?16 and transitions of the B-type bands with K_a^′=0,1, N^′?15 were assigned. The origin calculated from the best fit to the present spectrum is at which is ∼ higher than previously reported. The overtone spectrum is observed to be heavily perturbed, possibly by Fermi resonance with energy levels of the nearby (ν₂+5ν₃) state.     

Simultaneous dual-wavelength oscillation at 1357 nm and 1444 nm in a Kr-flashlamp pumped Nd:YAG laser

A Nd:YAG laser pumped by a Kr-flashlamp with simultaneous dual-wavelength operation at 1357 nm (⁴F_3/2 → ⁴I_13/2(R₁ → X₄)) and 1444 nm (⁴F_3/2 → ⁴I_13/2(R₁ → X₇)) is demonstrated and its characteristics was analyzed. The output energy of 82 mJ at 1357 nm and 138 mJ at 1444 nm were achieved simultaneously with the maximum electrical input energy of 44 J. Stability of the output energy in the dual-wavelength operation was 1.41% at the maximum input energy of 44 J. However, the stabilities at each wavelength in the dual-wavelength operation showed much lower stability.