Browsing by Author "Li, T."

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Open Access
808 nm broad-area laser diodes designed for high efficiency at high-temperature operation
(Institute of Physics Publishing Ltd., 2021-09-21) Lan, Y.; Yang, G.; Liu, Y.; Zhao, Y.; Wang, Z.; Li, T.; Demir, Abdullah
Semiconductor lasers with high power conversion efficiency (PCE) and output power are heavily investigated driven by more energy-efficient commercial applications. In this paper, an asymmetric broad area laser (A-BAL) design is studied and compared with a conventional symmetric broad area laser (S-BAL) design for 808 nm single emitter laser diodes. We present a comparative theoretical and experimental investigation by studying the thermal effects on the laser parameters. The output characteristics and efficiency loss paths for the designs were analyzed. The leakage of carriers was identified as the primary source of the PCE reduction with temperature. Suppressing this leakage by optimization of the A-BAL design, a record continuous-wave PCE of 68% at 25 °C and 60.4% at 75 °C were achieved for a single emitter laser with 10 W output power. These devices deliver high efficiency at high temperatures with reliable operation achieving 2000 h of an accelerated aging lifetime without failures.
Open Access
High-power operation and lateral divergence angle reduction of broad-area laser diodes at 976 nm
(Elsevier, 2021-04-28) Liu, Y.; Yang, G.; Wang, Z.; Li, T.; Tang, S.; Zhao, Y.; Lan, Y.; Demir, Abdullah
Broad-area diode lasers with high output power and low lateral divergence angle are highly desired for extensive scientific and industrial applications. Here, we report on the epitaxial design for higher output power and a flared waveguide design for reduced divergence, which leads to high power operation with a low lateral divergence angle. A vertically asymmetric epitaxial structure was employed and optimized for low internal optical loss and high efficiency to realize high output power operation. Using a flared waveguide design, the lateral divergence angle was efficiently reduced by decreasing the number of high-order lateral optical modes significantly. The flared waveguide design introduces a smooth modification of the ridge width along the cavity without deteriorating laser performance. Based on the optimized epitaxial and waveguide design, we scaled the waveguide width to realize high continuous-wave power of 34.5 W at 25 °C. A low lateral divergence angle of 8° and high power conversion efficiency of 60% were achieved at the operating power level of 25 W. The life test data (30 A at 45 °C for 39 units, 0 failures in 1000 h) demonstrated reliable operation illustrating the efficient design for reduced lateral divergence angle and high operating power.
Open Access
Investor attention and cryptocurrency market liquidity: A double-edged sword
(Springer, 2022-09) Yao, S.; Şensoy, Ahmet; Nguyen, D. K.; Li, T.
This paper explores the double-edged sword effect of investor attention on market liquidity. Based on the analysis on 597 cryptocurrencies from 2014 to 2020, our findings show that static investor attention improves cryptocurrency market liquidity over the next three months by attracting more investors into the market and stimulating buy and sell transactions. By contrast, abnormal attention persistently and negatively affects the liquidity and leads to excessive net buying pressure in the market and a crowded buyers’ market, resulting in a sharp deterioration of liquidity. Moreover, these effects intensify during low global economic policy uncertainty periods and for cryptocurrencies with small market capitalization and low idiosyncratic volatility. Overall, our results have important implications for investors, portfolio managers, and policymakers.
Open Access
Investor attention and environmental information disclosure quality: Evidence from heavy pollution industries in China
(John Wiley & Sons Ltd., 2023-03-20) Yao, S.; Li, T.; Şensoy, Ahmet; Fang, Z.; Cheng, F.
Using listed firms from 16 heavy pollution industries in China, we show that investor attention can significantly improve the quality of corporate environmental information disclosure. By examining the heterogeneity effects of investor attention under different firm characteristics, locations, and external supervision, we reveal that this improvement effect is more pronounced for smaller firms, state-owned enterprises, firms with weaker corporate governance, and firms located in China's western regions (regions with poor economic development). We further find that public's attention to environmental issues promotes the investor attention level on firms in heavy pollution industries, thus improving firms' environmental information disclosure quality. Overall, our results emphasize the role of external investor attention on corporate environmental issues.