Design and performance of a diode laser spectrometer for a stratospheric aircraft

We report the instrument description and the results of the laboratory calibration and tests of a mid-infrared tunable diode spectrometer for in situ trace gas concentration measurements in the stratosphere operating on a stratospheric aircraft. The spectrometer is dedicated to the measurement of the HNO3 amount in the stratospheric aerosols by means of gas-phase absorption spectroscopy on molecular roto-vibrational lines in the mid-infrared, using a tunable diode laser and a multipass absorption cell. The instrument was specifically designed for operation aboard of the stratospheric aircraft M55 Geophysica, in the frame of the Airborne Platform for Earth observation (APE) project. The instrument is part of a measurement package for the measurement of the chemical content of Polar Stratospheric Clouds (PSCs) and other atmospheric aerosols. This system can be also used as a stand-alone detector of molecular trace gases. Design criteria include an efficient optical layout, with a very low sensitivity to the vibration and thermal stresses and a very small footprint, and a detection scheme based on the sweep integration technique for fast data acquisition and high signal-to-noise (S/N) ratio. We report a new set of testing measurements on ammonia as the calibration gas with one order of magnitude improvement with respect to what we previously reported

Figure of merit for nonlinear materials in second-order cascaded nonstationary processes

In this paper, we present and discuss an extension and an improvement of the Figure of Merit (FoM) that we introduced in a previous paper. The FoM describes the effectiveness of the frequency doubling materials for ultrashort light pulse modulators via second-order cascaded effects. In the present work, as an input pulse we use a temporal Gaussian pulse so that our perturbative method allows an analytical expression even for the output pulse field after the second pass inside the crystal. For the first time together with the completely analytical expression for the second pass, we report also the exact numerical coefficients for the peak phase modulation. With the FoM it is possible to choose the more appropriate nonlinear material and the use of the cascaded interaction process. Finally, we present for the first time the FoM dependence from the wavelength in the interval 0.5–1 μm, and to a table already shown we added more nonlinear materials

Effects of the excitation density on the laser output of two differently doped Yb:YAG ceramics

We report the behavior of two Yb(3+) doped ceramics (i.e. 10% at. and 20% at.) under quasi-continuous wave laser pumping. Two different behaviors are found depending on the density of Yb(3+) in the excited level. Experimental results show that at low population inversion density, the maximum output power and the efficiency are almost independent on the doping concentration. In particular, an output power as high as 8.9 W with a corresponding slope efficiency of 52% with respect to the injected pump power was reached with the 20% at. sample. Conversely, at high population inversion densities, the 20% doped sample shows a sudden decrease of the laser output for increasing pump power, due to the onset of a nonlinear loss mechanism. Finally, we report a comparison of the experimental results with numerical simulations for the evaluation of the inversion density and of the temperature distribution

High efficiency laser action of 1% at. Yb 3+ :Sc 2 O 3 ceramic

We report the spectroscopic characteristics and the laser performances of a low-doped 1% at. Yb:Sc(2)O(3) ceramic sample. Under end- pumping at 933 nm and 968 nm in quasi-CW mode, at 1040.5 nm the laser delivers a maximum output power of 4.3 W and 1.77 W, respectively with a corresponding slope efficiency of 74% and 80%, which are, to the best of our knowledge, the highest value reported in literature for ceramics. We explored the tuning range of the sample, which spans from 1005 nm to 1050.5 nm, and finally we characterized the low losses tunable cavity at 1032 nm

Tunability enhancement of Yb:YLF based laser.

We present a comprehensive characterization of a laser, based on a high-quality heavily doped Yb:YLF crystal. The analysis includes the comparison of the laser efficiency in respect of the absorbed pump for both pi and sigma-polarization. In particular, for the tunable laser, we report an enhancement of the tuning range obtained by adapting the output coupler transmission in respect of the lasing wavelength. The experimental results obtained for various output coupling have also been compared with a numerical model in order to give information for a further enlargement of the tuning range

Experimental evidence of a nonlinear loss mechanism in highly doped Yb:LuAG crystal

We report a rigorous study of the spectroscopic, laser and thermal properties of a 10at.% and a 15at.% Yb:LuAG crystals. A loss mechanism is observed in the medium with the highest doping, pumped at 936 nm and 968 nm, as a sharp and dramatic decrease of the laser output power is measured at higher excitation densities. The nonlinearity of the loss mechanism is confirmed by the fluorescence data and by the thermal lens. In particular, the dioptric power of the thermal lens acquired at different pumping levels shows a strong deviation of the expected linear trend. Here we report the influence of both the concentration and the ion excitation density of Yb3+ on the output powers, the slope efficiencies and the thresholds. Conversely excellent results are achieved with the 10at.%, which does not show any loss mechanism as at 1046 nm it delivers 11.8 W with a slope efficiency of eta(s) = 82%, which is, to the best of our knowledge, the highest value reported in literature for this material. (C) 2014 Optical Society of Americ

Spectroscopy and CW first laser operation of Yb-doped Gd_3(Al_05Ga_05)_5O_12 crystal

We present the spectroscopic characterization and laser operation of a 2%at. Yb doped Gd3(Al0.5Ga0.5)5O12 (Yb:GAGG) crystal, grown with the Czochralski method. We determined the absorption and the emission spectrum, the upper level lifetime, and the thermal conductivity. The internal disordered structure determines a significant broadening of the emission band (12.1 nm FWHM) with respect to the parent composition Yb:GGG (8 nm FWHM). The laser performances were evaluated on an end pumped cavity, using a CW semiconductor laser as the pump source. We obtained a maximum slope efficiency of 60.8% and an optical to optical efficiency of 46.0%, with a maximum output power of 4 W, limited only by the available pump power. The tuning range extends from 995 nm to 1050 nm. To our knowledge this is the first spectroscopic investigation and the first assessment of the laser performance of an Yb:GAGG crystal with this composition (i.e. Al/Ga balance = 0.5/0.5)

High efficiency room temperature laser emission in heavily doped Yb:YLF

We report the tunable, CW and quasi CW laser operation at room temperature of an highly doped (30% at.) Yb:YLF crystal longitudinally pumped by a fiber coupled laser diode array. The CW output power is 1.15 W vs. an absorbed pump power of 6 W, with a slope efficiency of 31%. In quasi-CW operation (20% duty factor @10 Hz) an output power of 4 W with an absorbed power of 9.5 W, and a slope efficiency of 62.8% were obtained. The tuning range spans from 1022 to 1075 nm. To our knowledge, these are among the best experimental results obtained at room temperature with Yb doped YLF

Direct comparison of Yb3+:CaF2 and heavily doped Yb3+:YLF as laser media at room temperature.

We report an extensive comparison of the laser performances of diode-pumped Yb(3+):YLF (30% at.) and Yb(3+):CaF(2) (5% at.) crystals, lasing at room-temperature and operating in two different operation mode, i.e. Continuous Wave (CW) and quasi-CW. An in-depth investigation of the crystals behavior by changing the pump power, clearly shows the crystal absorption depends on the lasing conditions. Therefore, we report an unambiguous definition of the slope efficiency calculated taken into account the real measured crystal absorption under laser action. Finally, we present a study of problems related to thermally induced losses which are expected influencing the laser performance