光電所所訊

Laser-diode pumped glass-clad Ti:sapphire crystal fiber laser

Professor Sheng-Lung Huang’s laboratory

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

臺灣大學光電所黃升龍教授

Titanium (Ti):sapphire crystals have become one of the most widely used solid-state laser gain media. Their broadband emission spectra are suitable for a wide range of applications, such as tunable lasers and mode-locked lasers, although their low absorption cross section and short lifetime prevent them from low threshold operations. In this work, efficient glass-clad crystal fiber lasers were demonstrated using a Ti:sapphire crystalline core as the gain medium. With a core diameter of 18 μm, the laser diode (LD) pump source can be effectively coupled and guided throughout the crystal fiber for a low threshold and high slope efficiency laser operation. The advantage of high heat dissipation efficiency of the fiber structure can be derived from the low core temperature rising measurement (i.e. 17 K/W) with passive cooling. At an output transmittance of 23%, the lowest absorbed threshold of 118.2 mW and highest slope efficiency of 29.6% were achieved, with linear laser polarization.

Fig. 1. SEM images of (a) end face of a glass-clad Ti:sapphire crystal fiber and (b) side face of a Ti:sapphire crystalline core; TEM images of (c) crystalline sapphire core and (d) interface of core and borosilicate clad. Dashes outline the 2-nm overlapping layer.

Fig. 2. (a) 520-nm LD pumped glass-clad Ti:sapphire crystal fiber laser scheme, (b) L-I curve by 520-nm LD pumping, (c) lasing spectra at different pump powers, (d) laser polarization measurement, and (e) lasing transverse mode profile. LPF: long wavelength pass filter; the red line in (b) is the simulation result. PM: power meter; OSA: optical spectrum analyzer.

Reference:

S. C. Wang, C. Y. Hsu, T. T. Yang, D. Y. Jheng, T. I Yang, T. S. Ho, and S. L. Huang, “Laser-diode pumped glass-clad Ti:sapphire crystal fiber laser,” Optics Letters, 41, pp. 3217–3220, 2016.

Noninvasive third harmonic generation microscopy reveals the dietary evolution in the ultrastructure of dinosaur teeth

Professor Chi-Kuang Sun

Graduate Institute of Photonics and Optoelectronics, National Taiwan University

臺灣大學光電所孫啟光教授

Fossilized teeth are primary tools in the study of vertebrate evolution, but standard imaging modalities have not been able to provide high-quality image contrast and 3D information inside dentin, the main component of teeth, owing to small refractive index differences in the fossilized tissues. Our first attempt to use third harmonic generation (THG) microscopy in numerous fossil teeth, spanning 300 Ma of vertebrate history, has yielded significant submicron level anatomy, with an unexpectedly strong THG signal contrasting fossilized tubules from the surrounding dentin. Morphometric analyses of dentinal tubule diameter, density, and branching rates provide strong phylogenetic signatures and reveal patterns consistent with evolutionary relationships among various groups of amniotes, including dinosaurs. These morphometric analyses reveal a strong signal for dietary preferences, with herbivorous saurischian and ornithischian dinosaurs consistently having higher dentinal tubule density than their carnivorous relatives. We hypothesize that this relates to the hardness of the dentine, where herbivorous taxa have dentine that is more resistant to breakage and wear at the dentine-enamel junction than carnivorous taxa. Our results also represent the only successful imaging of dentinal tubules in fossilized tissues while maintaining a sub-micron resolution, providing non-invasive 3D histological reconstruction in intact fossil teeth, demonstrating the great potential of our developed harmonic generation microscopy for the evolutionary studies of vertebrates. This work is in collaboration with Robert R. Reisz, University of Toronto Mississauga, Canada, Dar-Bin Shieh, National Cheng Kung University, and Timothy D. Huang, a dinosaur lover.

Figure 1: One of the Harmonic Generation Microscopes (HGM) built and designed in Prof. Sun’s laboratory. HGM was designed for noninvasive clinical microscopy imaging on human skin and mucosa, while with a world-record performance on resolution, penetration depth, and bio-viability. Its operating wavelength is at 1260 nm, and can penetrate even the darkest skin. Obviously it is also perfect for fossil studies.

Figure 2: Optically-sectioned 2D third-harmonic-generation microscopic images of the dentine-enamel junction from various fossil teeth. All scale bars, 20 μm. For animal’s outlook and their ages, please refer to Figure 3 and Figure 4. For 3D images, please refer to our references.

Figure 3: The imagination reconstruction of the ancient vertebrates where our fossil teeth came from. One to one correspondence on the relative position with respect to Figure 2 can be found. We appreciate all the sources where the pictures are from.

Figure 4: Results of morphometric analysis of dentinal tubules. (A) Bivariate plot of dentinal tubule density mean, tubule branching mean, and diameter. The sizes of the colored circles are representative of tubule diameter. The colors of the circles match the taxa in the phylogeny (B), which contains all taxa examined in this study. a, Cotylosauria; b, Amniota; c, Synapsida; d, Archosauria; e, Crocodylia; f, Dinosauria; g, Ornithischia; h, Saurischia. Abbreviation: Ma, Millions of years.

Reference:

Y.-C. Chen, S.-Y. Lee, Y. Wu, D.-B. Shieh, K. Brink, T. D. Huang, R. R. Reisz, and C.-K. Sun, “Third harmonic generation microscopy reveals dental anatomy in ancient fossils,” Optics Letters 40 (7), pp. 1354-1357 (2015).

K. S. Brink, Y.-C. Chen, Y.-N. Wu, W.-M. Liu, D.-B. Shieh, T. D. Huang, C.-K. Sun, and R. R. Reisz, “Dietary adaptions in the ultrastructure of dinosaur dentine,” to appear in Journal of the Royal Society Interface.