Title: Design and Development of Pulsed Cascaded Raman Fiber Lasers and Supercontinuum Sources and Applications in Photoacoustic Imaging and Semiconductor Metrology
Name: Abhigyan Goswami
Advisors: Prof. VR Supradeepa (CeNSE) and Prof. Baladitya Suri (IAP)
Date: 20th February 2026
Time: 4:00 PM
Venue: CeNSE Seminar Hall
Abstract: Can a single multi-color laser platform replace multiple fixed-color laser sources?
In this thesis colloquium, we will discuss the design and development of advanced high-power fiber laser systems and their applications in biomedical imaging and semiconductor metrology. The conventional rare-earth-doped fiber lasers are often lagged in deployment for such applications due to limited wavelength tunability. To address this, we will demonstrate two wavelength agile fiber laser platforms, cascaded Raman fiber lasers (CRFL) and supercontinuum sources, operating in two of the most important wavelength bands, the entire second near-infrared window (NIR-II, 1-1.6 um) and in the visible window (530-600 nm). Their successful integration into application-specific systems will be demonstrated.
1. Cascaded Raman fiber laser for biomedical imaging
On the biomedical side, we will highlight photoacoustic imaging (PAI)—a non-invasive, in-vivo imaging modality that combines optical absorption contrast with ultrasonic penetration depth. Conventional PAI systems rely on multiple discrete laser sources to target different tissues. We will show how a single wavelength-tunable fiber laser source (40-200 ns pulse width, ~10 µJ pulse energy) can replace this complexity but also can enable chemical differentiation through fine wavelength tuning. We demonstrate photoacoustic spectroscopy of a lipid, cholesterol, in the 1200 nm band, a capability previously limited to bulky and inaccessible OPO-based systems.
Tunable visible lasers
The wavelength reach was further extended into the visible window through nonlinear frequency conversion, enabling access to additional chromophores. With a green-to-red visible source, delivering ~uJ pulse energy, we successfully differentiated two visible inks, blue and red, with contrasting absorption spectra, demonstrating hyperspectral photoacoustic imaging across the two most important wavelength bands, visible and NIR-II.
2. Supercontinuum source for semiconductor metrology
We further developed a semiconductor metrology solution for non-contact temperature measurement of silicon wafers, using the temperature dependence of silicon’s IR absorption. Achieving ~1 °C accuracy from room temperature to 600 °C at high acquisition speeds is challenging, often necessitating multiple laser sources, increasing system complexity, and reducing measurement speed. We propose the use of a compact, cost-effective telecom fiber-based supercontinuum, a white light source, whose spectrum can be tailored, that can replace multiple lasers. We demonstrate that a spectral shape with exponential roll-off towards longer wavelengths significantly enhances measurement accuracy. We achieve ∼1 °C accuracy, with a large measurement range (30-550 °C), with a fast acquisition speed of ~66 ms (detector speed limited). This can facilitate next-generation fabrication equipment development, enabling a ±1 °C temperature uniformity across 300 mm wafers, improving upon current industry standards of ±3 °C.
Bio:
Abhigyan is a PhD student at the Indian Institute of Science (IISc), working under the supervision of Prof. VR Supradeepa (CeNSE) and Prof. Baladitya Suri (IAP). His research focuses on the design and development of advanced fiber laser systems, with particular emphasis on wavelength-agile and high-power lasers and their applications in biomedical imaging and semiconductor metrology