The aim of my PhD research was to design low-noise, high-speed, lock-in-based multichannel acquisition systems for ultrafast spectroscopy applications. Ultra-short pulsed lasers are widely used in spectroscopy for their ability to concentrate energy within extremely short time windows, enabling high power excitation and precise temporal resolution. These characteristics make them suitable for techniques such as Stimulated Raman Scattering Microscopy and Time-Resolved Pump-Probe Spectroscopy. The first part of my PhD focused on designing an innovative 76-channel acquisition system for coherent Raman imaging, combining a low-noise differential front-end based on the lock-in technique with parallel acquisition and real-time data processing. This work was conducted as part of the CRIMSON project, funded by the European Union Horizon 2020 research and innovation program under grant agreement No. 101016923. The project, led by Prof. Dario Polli from the Physics Department of Politecnico di Milano, aims to develop an innovative Raman microscope for real-time, non-invasive imaging of cells and tissues. This technology has the potential to revolutionize biology and medicine, particularly in tumor identification and analysis. To achieve this goal, an ASIC implementing an 8-channel readout circuit was designed. The integrated circuit was tested and incorporated into the acquisition system, enabling parallel processing of signals from photodiode arrays through an automatically balanced differential lock-in architecture, significantly reducing optical noise. The system is capable of acquiring a 76-wavelength Raman spectrum spatially distributed across a photodiode array, where each wavelength is detected by a dedicated element. The architecture is modular, consisting of ten 8-channel modules connected to a motherboard. An Artix-7 FPGA generates control signals, implements a digital signal processing chain for offset cancellation and adjustable lock-in bandwidth, and manages USB communication with a PC. Finally, the complete Raman microscope system, from optics to electronics, was successfully validated. In the later phase of the PhD, the research focused on developing a new spectrometer for pump-probe spectroscopy. Current instruments are limited in acquisition speed due to the use of CCDs and low repetition-rate lasers (in the kHz range). The objective was to design electronics for a system capable of acquiring up to 40 wavelengths in parallel with a resolution of 1 ppm. The spectrometer includes two ASICs for signal amplification and processing, along with a PCB for data conversion and transmission to a PC. A key feature of the integrated circuits is preliminary signal processing, which relaxes the requirements for analog-to-digital conversion. This work builds on a flexible 20-channel ASIC (ECLIPSE) developed by a previous PhD student. I designed the supporting electronics, including the PCB and firmware, to control two ECLIPSE ASICs operating in parallel. An Artix-7 FPGA was used to manage communication between the PC and the acquisition system. After implementing firmware for 40 wavelengths, I developed a graphical user interface in C# to enable data acquisition, visualization, and storage. Finally, in collaboration with the Physics Department, the system was optically validated through the acquisition of real spectra.
Il dottorato ha riguardato la progettazione di sistemi di acquisizione multicanale a basso rumore e ad alta velocità, basati su tecnica lock-in, per applicazioni di spettroscopia ultrarapida. Nella prima fase è stato sviluppato un sistema innovativo a 76 canali per imaging Raman coerente, nell’ambito del progetto europeo CRIMSON. Il sistema combina un front-end differenziale a basso rumore, acquisizione parallela ed elaborazione dati in tempo reale. È stato progettato un ASIC a 8 canali, integrato in un’architettura modulare controllata da FPGA, in grado di acquisire simultaneamente diverse lunghezze d’onda con elevata sensibilità. L’intero microscopio Raman è stato successivamente validato sperimentalmente. Nella seconda fase è stato sviluppato uno spettrometro per spettroscopia pump-probe ad alta velocità. È stata progettata l’elettronica di un sistema capace di acquisire fino a 40 lunghezze d’onda in parallelo, basato su ASIC esistenti (ECLIPSE), FPGA e una nuova interfaccia software in C#. Anche questo sistema è stato validato mediante misure sperimentali reali.
Low-noise, multichannel, electronic instrumentation for broadband optical spectroscopy applications
GUBELLO, GIULIO
2025/2026
Abstract
The aim of my PhD research was to design low-noise, high-speed, lock-in-based multichannel acquisition systems for ultrafast spectroscopy applications. Ultra-short pulsed lasers are widely used in spectroscopy for their ability to concentrate energy within extremely short time windows, enabling high power excitation and precise temporal resolution. These characteristics make them suitable for techniques such as Stimulated Raman Scattering Microscopy and Time-Resolved Pump-Probe Spectroscopy. The first part of my PhD focused on designing an innovative 76-channel acquisition system for coherent Raman imaging, combining a low-noise differential front-end based on the lock-in technique with parallel acquisition and real-time data processing. This work was conducted as part of the CRIMSON project, funded by the European Union Horizon 2020 research and innovation program under grant agreement No. 101016923. The project, led by Prof. Dario Polli from the Physics Department of Politecnico di Milano, aims to develop an innovative Raman microscope for real-time, non-invasive imaging of cells and tissues. This technology has the potential to revolutionize biology and medicine, particularly in tumor identification and analysis. To achieve this goal, an ASIC implementing an 8-channel readout circuit was designed. The integrated circuit was tested and incorporated into the acquisition system, enabling parallel processing of signals from photodiode arrays through an automatically balanced differential lock-in architecture, significantly reducing optical noise. The system is capable of acquiring a 76-wavelength Raman spectrum spatially distributed across a photodiode array, where each wavelength is detected by a dedicated element. The architecture is modular, consisting of ten 8-channel modules connected to a motherboard. An Artix-7 FPGA generates control signals, implements a digital signal processing chain for offset cancellation and adjustable lock-in bandwidth, and manages USB communication with a PC. Finally, the complete Raman microscope system, from optics to electronics, was successfully validated. In the later phase of the PhD, the research focused on developing a new spectrometer for pump-probe spectroscopy. Current instruments are limited in acquisition speed due to the use of CCDs and low repetition-rate lasers (in the kHz range). The objective was to design electronics for a system capable of acquiring up to 40 wavelengths in parallel with a resolution of 1 ppm. The spectrometer includes two ASICs for signal amplification and processing, along with a PCB for data conversion and transmission to a PC. A key feature of the integrated circuits is preliminary signal processing, which relaxes the requirements for analog-to-digital conversion. This work builds on a flexible 20-channel ASIC (ECLIPSE) developed by a previous PhD student. I designed the supporting electronics, including the PCB and firmware, to control two ECLIPSE ASICs operating in parallel. An Artix-7 FPGA was used to manage communication between the PC and the acquisition system. After implementing firmware for 40 wavelengths, I developed a graphical user interface in C# to enable data acquisition, visualization, and storage. Finally, in collaboration with the Physics Department, the system was optically validated through the acquisition of real spectra.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/256137