Abstract-Terahertz synthetic aperture in-line holography with intensity correction and sparsity autofocusing reconstruction

Zeyu Li, Ruijiao Zou, Weipeng Kong, Xuemin Wang, Qinghua Deng, Qiang Yan, Yu Qin, Weidong Wu, and Xun Zhou

Synthetic aperture hologram with intensity correction for a dragonfly forewing. (a) Nine normalized sub-holograms with intensity correction. (b) Synthetic aperture hologram composed of (a). (c) Synthetic aperture hologram without intensity correction. (d) Optical image of the dragonfly forewing sample. (e) Amplitude distribution reconstructed from (b) with 20 iterations. (f) Amplitude distribution reconstructed from (c) with 20 iterations. The effect of non-uniform intensity on reconstruction can be seen from the parts marked by the white and blue dotted circles.

https://www.osapublishing.org/prj/abstract.cfm?uri=prj-7-12-1391

We demonstrate high-resolution and high-quality terahertz (THz) in-line digital holography based on the synthetic aperture method. The setup is built on a self-developed THz quantum cascade laser, and a lateral resolution better than 70 μm (∼𝜆$\sim \lambda$) is achieved at 4.3 THz. To correct intensity differences between sub-holograms before aperture stitching, a practical algorithm with global optimization is proposed. To address the twin-image problem for in-line holography, a sparsity-based phase retrieval algorithm is applied to perform the high-quality reconstruction. Furthermore, a new autofocusing criterion termed “reconstruction objective function” is introduced to obtain the best in-focus reconstruction distance, so the autofocusing procedure and the reconstruction are unified within the same framework. Both simulation and experiment prove its accuracy and robustness. Note that all the methods proposed here can be applied to other wavebands as well. We demonstrate the success of this THz synthetic aperture in-line holography on biological and semiconductor samples, showing its potential applications in bioimaging and materials analysis.

© 2019 Chinese Laser Press

Abstract-Fabrication of 4.4 THz quantum cascade laser and its demonstration in high-resolution digital holographic imaging

Tao Jiang, Changle Shen, Zhiqiang Zhan, Ruijiao Zou, Jia Li, Long Fan, Tingting Xiao, Weihua Li, Qing hua Deng, Liping Peng, Xuemin Wang, Weidong Wu,



https://www.sciencedirect.com/science/article/pii/S0925838818331797

In this work, we present our research on the fabrication of high power terahertz quantum cascade laser (THz QCL) with frequency at 4.4 THz and its demonstration in digital holographic imaging. The lasers described in this work are based upon the resonant-phonon active region design and semi-insulating surface-plasmon waveguide. The peak power varies with the size of the ridge and the maximum output power of 95 mW at 10 K in pulsed mode is obtained. The maximum working temperature is 80 K. Interestingly, by changing the injection current, the transverse mode of the laser can be switched between TM00 mode and TM01 mode. With such THz QCL as the light source, the lateral resolution of a home-built digital holographic imaging system can reach 80 μm.