CCD and CMOS detectors in LIBS

CCD

The technology, of Charged-couped device (CCD) sensor, is based on quick shift of the charge stored in the image region. The stored charge is shifted one row at a time into readout section. Then the stored charge in each pixel is moved sequentially toward an output node (A/D convertor) and measured.

In this way, a charge map or image is constructed. These capabilities can be extended by various configurations beyond the basic detector model. For instance, Intensified CCD can rapidly gate, achieving the range exceeding 104 .Images, however, are not as sharp as typical CCD camera, because of crosstalk. Meanwhile, Electron multiplying CCDs stand out for higher sensitivity at a lower cost, with their preamplification stages ensuring signal enhancement before digital conversion.  

The various noise sources present in a CCD output measurement are either single-related (shot-noise) or device-related (dark current, charge transfer losses, reset noise , etc). In LIBS these effects can be terminated by several techniques, including colling the detector, gating (ability to control the exposure time of the sensor to light with extremely high precision), software correction, etc. 

The future trends for CCD detectors in LIBS are likely to involve advancements in sensitivity, resolution, and speed, alongside a push towards more compact and integrated systems. Developments might include improvements in the CCD manufacturing process to enhance light capture efficiency and reduce noise. Additionally, there may be a focus on making CCD-based LIBS systems more affordable and accessible for a wider range of applications.

source: https://semiengineering.com/cmos-image-sensors-cis-past-present-future/

CMOS

Complementary Metal-Oxide Semiconductor (CMOS) is made of an array of pixels, which measure the intensity of light from each pixel and convert it into electrical signals. These signals are then processed by the camera’s A/D converter to create a digital image. Unlike CCD, CMOS sensor is not limited to silicon, it can incorporate various materials, allowing for sensitivity across UV visible and IR light spectrums. 

The architecture of the CMOS sensors offers several benefits. For instance, the direct pixel readout demands less energy than CCD’s serial charge transfer. Each pixel works independently, which brings faster readout speeds, supporting rapid image capture and high frame rates. 

Given these advantages over CCD, CMOS sensors are increasingly being used in LIBS. The compact size, lightweight of CMOS sensors is suitable for compact and portable LIBS instruments. Historically CMOS sensors exhibited higher noise levels than CCDs, although the development of CMOS technology has significantly narrowed this gap. 

In conclusion, CMOS detectors have made a name in the field of imaging technology, standing out for their efficiency, speed, and integration capabilities. Thanks to the technology development, these detectors are set to further narrow the performance gap with CCDs, potentially becoming the go-to choice for a broader spectrum of applications, including (but not limited) to LIBS, especially in industrial online production monitoring.

However, the usage of CCD and their modified variants (ICCD and EMCCD) is still essential for more advanced or scientific applications (like nuclear or medical research) thanks to their low noise level, higher sensitivity and more detailed resolution.