Duchang Heo

This paper describes a study on a novel X-ray detector with photoinduced discharge (PID) readout devices. Especially, we demonstrated optical scanning X-ray imaging devices based on intrinsic hydrogenated amorphous silicon (i-a-Si:H) PID readout layer, on which a pixelated metal layer, molybdenum, is formed as a charge accumulation layer of 200 μm pitch for clearly defining the pixel in the lateral and longitudinal directions. We decided to use i-a-Si:H as a readout layer instead of amorphous selenium(a-Se) layer because the material of a-Se does not withstand standard wet fabrication processes like lift-off wet process. An X-ray absorption layer of 500 μm thick a-Se is formed by a thermal evaporation process. To optically switch on the i-a-Si:H PID readout layer, we use a narrow line-beam with a beam width of 50 μm consisting of a blue LED array, optical films, and GRIN lens array. The pixelated PID readout X-ray detector is 512 x 512 image resolutions with a 200 μm pitch, and the overall active dimension is 10.24 cm x 10.24 cm. The sensitivity of the pixelated PID readout X-ray detector is 302 pC/cm2∙mR at Normal X-ray Tube conditions (IEC66220-1). According to MTF measurement results, the value of MTF0.1(10%) is measured at near 2.5 1/mm in the column direction scanning while the value is measured at 1.9-2.5 1/mm in the row direction scanning.

A Micro holes in a diamond are presented by using a homemade femtosecond (fs) Yb:KGW laser. An fs laser source was used emitting pulse duration of 230 fs at 1030 nm wavelength, whereas the spot size amounted to 8.9 μm. Parameters like pulse energy, and pulse number were varied over a wide range in order to evaluate their influence both on the micro hole geometry like hole diameter, circularity, taper angle, and on the drilling quality. Hourglass-shaped micro holes whose diameters decrease and increase again after a certain depth have important applications. The results demonstrate the feasibility of extending the drilling of an hourglass-shaped hole in a diamond sample, which has similar diameters at the hole entrance (92 μm) and exit (95 μm), but a much smaller diameter (28 μm) at a certain waist section inside the hole.

We developed a novel direct X-ray detector using photoinduced discharge (PID) readout for digital radiography. The pixel resolution is 512 × 512 with 200 μm pixel and the overall active dimensions of the X-ray imaging panel is 10.24 cm × 10.24 cm. The detector consists of an X-ray absorption layer of amorphous selenium, a charge accumulation layer of metal, and a PID readout layer of amorphous silicon. In particular, the charge accumulation is pixelated because image charges generated by X-ray should be stored pixel by pixel. Here the image charges, or holes, are recombined with electrons generated by the PID method. We used a 405 nm laser diode and cylindrical lens to make a line beam source with a width of 50 μm for PID readout, which generates charges for each pixel lines during the scan. We obtained spatial frequencies of about 1.0 lp/mm for the X-direction (lateral direction) and 0.9 lp/mm for the Y-direction (scanning direction) at 50% modulation transfer function.