Fabrication and characterization of iodine photonic microcells for sub-Doppler spectroscopy applications.

We report on the development of all-fiber stand-alone iodine-filled photonic microcells demonstrating record absorption contrast at room temperature. The microcell's fiber is made of inhibited coupling guiding hollow-core photonic crystal fibers. The fiber-core loading with iodine was undertaken at 10-1-10-2mbar vapor pressure using what, to the best of our knowledge, is a novel gas-manifold based on metallic vacuum parts with ceramic coated inner surfaces for corrosion resistance. The fiber is then sealed on the tips and mounted on FC/APC connectors for better integration with standard fiber components. The stand-alone microcells display Doppler lines with contrasts up to 73% in the 633 nm wavelength range, and an off-resonance insertion loss between 3 to 4 dB. Sub-Doppler spectroscopy based on saturable absorption has been carried out to resolve the hyperfine structure of the P(33)6-3 lines at room temperature with a full-width at half maximum of 24 MHz on the b4 component with the help of lock-in amplification. Also, we demonstrate distinguishable hyperfine components on the R(39)6-3 line at room temperature without any recourse to signal-to-noise ratio amplification techniques.

Contaminant-free end-capped and single-mode acetylene photonic microcell for sub-Doppler spectroscopy.

We report on the development of an acetylene-filled photonic microcell based on an assembly process that is contaminant free and requires no helium buffer gas nor gluing procedure. The microcell consists of a 7-m-long and 30 µm core-diameter inhibited-coupling guiding hollow-core photonic crystal fiber filled with acetylene gas at a pressure in the range of 80 µbar, sealed by capping its ends with fusion-collapsing a glass-tube sleeve, and mounted on FC connectors for integration. The microcell shows a robust single-mode behavior and a total insertion loss of ∼1.5dB. The spectroscopic merit of the formed microcell is tested by generating electromagnetic induced transparency and saturated absorption on R13 and P9 absorption lines, respectively. The sub-Doppler transparencies show a close to transit time limited linewidth of 17±3MHz. The latter was monitored for over 3 months. As a demonstration, the microcell was used to frequency stabilize a laser with fractional frequency instability improvement by a factor 50 at 100 s integration time compared to free running laser operation.

Stress-induced optical waveguides written by an ultrafast laser in Nd3+, Y3+ co-doped SrF2 crystals.

In this paper, we report on the ultrafast laser-induced birefringence, refractive index changes, and enhanced photoluminescence properties in the volume of neodymium (Nd), yttrium (Y) co-doped strontium fluoride (SrF2) and Nd, Y co-doped calcium fluoride (CaF2) crystals. The optical waveguides written with 500 kHz repetition rate provided lowest propagation loss of 1.63±0.21 dB cm-1 for transverse magnetic (TM) polarization at 632.8 nm in Nd,Y:SrF2 crystal. The measured retardance can be interpreted by stress-induced birefringence related to the permanent volume expansion, photo induced by a non-spherical irradiated zone. The absorption, steady-state, and time-resolved photoluminescence properties are also carried out in and out of the laser irradiated zone, enabling the local changes of the Nd and Y network in Nd,Y:SrF2, as well as well-preserved Nd fluorescence in the written optical waveguides.

Microsegregation Model Including Convection and Tip Undercooling: Application to Directional Solidification and Welding.

The microsegregation behavior of alloy filler metal 52 (FM 52) was studied using microprobe analysis on two different solidification processes. First, microsegregation was characterized in samples manufactured by directional solidification, and then by gas tungsten arc welding (GTAW). The experimental results were compared with Thermo-Calc calculations to verify their accuracy. It was confirmed that the thermodynamic database predicts most alloying elements well. Once this data had been determined, several tip undercooling calculations were carried out for different solidification conditions in terms of fluid flow and thermal gradient values. These calculations allowed the authors to develop a parametrization card for the constants of the microsegregation model, according to the process parameters (e.g., convection in melt pool, thermal gradient, and growth velocity). A new model of microsegregation, including convection and tip undercooling, is also proposed. The Tong⁻Beckermann microsegregation model was used individually and coupled with a modified Kurz-Giovanola-Trivedi (KGT) tip undercooling model, in order to take into account the convection in the fluid flow at the dendrite tip. Model predictions were compared to experimental results and showed the microsegregation evolution accurately.