https://dspace.iiti.ac.in/handle/123456789/9535 Fri, 23 Oct 2026 10:31:44 GMT 2026-10-23T10:31:44Z https://dspace.iiti.ac.in/handle/123456789/19505 Title: Rare- earth doped glass ceramic-based scintillators [RESTRICTED THESIS-06 Months] Authors: Gouri Suresh Abstract: [Abstract is restricted for 06 Months, due to IPR related issue] Fri, 22 May 2026 00:00:00 GMT https://dspace.iiti.ac.in/handle/123456789/19505 2026-05-22T00:00:00Z https://dspace.iiti.ac.in/handle/123456789/19504 Title: Development of a closed-loop control system for laser-directed energy deposition (L-DED) of stellite alloy Authors: Sharma, Rakshit Abstract: Laser-Directed Energy Deposition (L-DED) of superalloys like Stellite-21 is widely used in aerospace, defence and energy industries for precision repair, cladding, and restoration of high-value components. Stellite-21, a cobalt-chromium-molybdenum alloy, offers excellent high-temperature wear resistance and chemical stability, making it ideal for turbine blade repair and engine component refurbishment. However, achieving consistent geometric accuracy, dimensional stability and defect free deposition remains a fundamental challenge. The principal causes are highly nonlinear thermal effects, standoff-drift, laser-material interaction & dynamic melt pool emissivity. This thesis presents the design, development and experimental validation of a real time, three pillar closed loop control system for L-DED of Stellite-21 deployed on the TVASHTR five axis L-DED facility at the RRCAT, Indore. Tue, 12 May 2026 00:00:00 GMT https://dspace.iiti.ac.in/handle/123456789/19504 2026-05-12T00:00:00Z https://dspace.iiti.ac.in/handle/123456789/19478 Title: Preliminary studies related to balanced homodyne detection of squeezed light Authors: Pawar, Nishant Abstract: The objective of this project is to investigate experimental requirements for quantum noise limited balanced homodyne detection at 1064 nm, with the long term goal of supporting future squeezed light measurements for precision interferometry and gravitational wave detection. The work focuses on developing a low noise balanced detection platform capable of resolving quantum noise above the electronic background. The main experimental work consisted of photon shot noise and vacuum noise measurements using balanced photodetectors. Initial measurements with a fiber-coupled balanced photodetector showed the expected increase of noise with optical power, but the results exhibited relatively large fluctuations and incomplete suppression of classical noise. Improved performance was obtained using a free-space balanced photodetector. In the balanced configuration, the measured voltage noise spectral density showed close agreement with the theoretical shot noise prediction and significantly reduced measurement scatter, indicating effective rejection of common mode classical noise. Vacuum noise measurements in a balanced homodyne configuration further showed that the clearance above the electronic dark noise floor improved from about 1.43 dB at 50 μWlocal oscillator power to about 5.4 dB at 440 μW. These results demonstrate that the present detection system provides a practical foundation for future squeezed light measurements at the few-dB level. Keywords: photon shot noise, vacuum fluctuations, balanced homodyne detection, squeezed light, balanced photodetector. Mon, 11 May 2026 00:00:00 GMT https://dspace.iiti.ac.in/handle/123456789/19478 2026-05-11T00:00:00Z https://dspace.iiti.ac.in/handle/123456789/19477 Title: Energy scaling and pulse compression of ultrashort pulses in ytterbium doped fiber amplifier Authors: Singh, Ankit Kumar Abstract: This thesis presents the design, construction, and experimental characterisation of a compact Ytterbium-doped fiber-based regenerative amplifier (RGA) setup for energy scaling of ultrashort pulses at 1064 nm. The system employs a hybrid architecture, integrating in-fiber optical components for amplification and a free-space section for polarisation-based pulse picking using a Pockels cell. The work was carried out in two principal phases. In the first phase, a gain-switched diode laser (GSDL) delivering 50 ps pulses served as the seed source, enabling systematic characterisation of the regenerative cavity, including regenerative amplifier performance, free-space collimator coupling efficiency, Pockels cell-based pulse picking, and cavity roundtrip dynamics. Successful regenerative amplification was achieved (~ 100 times energy amplification) at repetition rates of 270 kHz. In the second phase, the GSDL seed was replaced with an in-house developed all-fiber mode-locked oscillator (repetition rate 32 MHz, pulse duration ~10 ps) to enable energy scaling of mode-locked pulses. With this configuration, energy amplification of ~ 900 times was achieved. The pulse width broadened during multi-pass amplification due to dispersion in fibers. Thus, the amplified pulses were directed to a grating-pair based pulse compressor for dispersion compensation, which compressed the amplified pulses from ~54 ps to ~14 ps. This work demonstrates a fully functional fiber-based RGA setup capable of producing high-energy ultrashort pulses suitable for a range of applications ranging from industrial applications to laboratory research, including micromachining, nonlinear microscopy, ultrafast spectroscopy, molecular dynamics etc. Mon, 11 May 2026 00:00:00 GMT https://dspace.iiti.ac.in/handle/123456789/19477 2026-05-11T00:00:00Z