In this letter, we report the antireflection and light absorption enhancement by forming sub-wavelength nano-patterned Si structures via nano-sphere lithography technique. It is found that the surface reflection can be significantly suppressed in a wide spectral range (400-1000 nm) and the weighted mean reflection is less than 5%. Meanwhile, the broad band optical absorption enhancement is achieved consequently. Heterojunction solar cells are prepared by depositing ultrathin amorphous Si film on the nano-patterned Si structures, the short circuit current density increases to 37.2 mA/cm(2)and the power conversion efficiency is obviously improved compared to the reference cell on flat Si substrate.
We present a diode-pumped quasi-three-level neodymium-doped yttrium aluminum garnet (Nd:YAG) laser at 885 nm, based on the 4F3/2-4I9/2 transition, generally used for a 946 nm emission. Combined with polarization components (Nd:YAG), the electro-optical crystal KH2PO4 (KDP) formed a Lyot filter in the cavity and compressed the available gain bandwidth. With an incident pump power of 9.2 W, a 714 mW continuous-wave (CW) output at 885 nm was achieved, and the optical-to-optical efficiency was 7.8%. With an adjustable voltage applied to the KDP crystal, the laser wavelength could be tuned from 885 nm to 884 nm. A simultaneous dual-wavelength Nd:YAG laser at 885 nm and 884 nm was also realized by adjusting the free spectral range of the Lyot filter. To our knowledge, it is the first study that has realized the tuning between the 884 and 885 nm lines and the simultaneous dual-wavelength CW laser operation at 885 nm and 884 nm.
Although the nanoscale world can already be observed at a diffraction-unlimited resolution using far-field optical microscopy, to make the step from microscopy to lithography still requires a suitable photoresist material system. In this letter, we consider the threshold to be a region with a width characterized by the extreme feature size obtained using a Gaussian beam spot. By narrowing such a region through improvement of the threshold sensitization to intensity in a high-threshold material system, the minimal feature size becomes smaller. By using platinum as the negative photoresist, we demonstrate that high-threshold lithography can be used to fabricate nanowire arrays with a scalable resolution along the axial direction of the linewidth from the micro- to the nanoscale using a nanosecond-pulsed laser source with a wavelength λ0 = 1064 nm. The minimal feature size is only several nanometers (sub λ0/100). Compared with conventional polymer resist lithography, the advantages of high-threshold lithography are sharper pinpoints of laser intensity triggering the threshold response and also higher robustness allowing for large area exposure by a less-expensive nanosecond-pulsed laser.
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