Black Quartz for Infrared Photodetection

Broadband infrared photodetection is highly relevant in various important fields, including imaging, optical communication, and spectroscopy. However, most commercially available photodetectors, such as those based on semiconductor materials, are constrained by a significant trade-off between their detection bandwidth and responsivity. A promising alternative medium for infrared photodetection is quartz, owing to its notable thermo-piezoelectric properties [1], which enable its use as a photodetector for wavelengths above <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$5\ \upmu \mathrm{m}$</tex>, where quartz exhibits strong absorption. In this work, we report a method to extend the absorption spectrum of quartz to wavelengths below the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$5\ \upmu \mathrm{m}$</tex> threshold, thereby achieving continuous photodetection across the Near- to Far-Infrared range. This approach, hereafter referred to as Black Quartz, involves the use of ultrafast pulsed laser processing to create superficial micro-patterns on quartz wafers. The employed laser source was a femtosecond laser system with emission centered at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\lambda=1030$</tex> nm. This system, coupled with a galvo-scanner, was used to imprint localized matrix patterns on the target wafers, with the matrix elements consisting of laser-irradiated spots. Two distinct types of spots were investigated: ablated craters and spots modified by localized Laser-Induced Periodic Surface Structures (LIPSS) [2], [3]. Various matrices, each composed of one of these two types of spots, were fabricated by varying the number of laser pulses per spot, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$N$</tex> and the center-to-center distance, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$h$</tex>, between adjacent spots. The laser pulse duration, fluence, and repetition rate were kept constant at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\tau_{P}=200$</tex> fs, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$F=10\ \mathrm{J}/\text{cm}^{2}$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$f=100\ \text{kHz}$</tex>, respectively. The optical spectra of the patterned matrices were measured using a laser transmission setup, employing five different laser sources covering the 1 to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$10.5\ \upmu \mathrm{m}$</tex> wavelength range. Figure 1 shows an image of one of these matrices alongside the optical spectra of all the fabricated matrices.