Development of ultrafast Raman lasers
thesisposted on 28.03.2022, 18:35 by Aravindan Madhava Warrier
Ultrafast lasers have made a tremendous impact on our lives, impacting a spectrum of applications like communication, medicine, defence, material processing and security. It took many years after the inception of the laser to reach the ultrafast domain of picoseconds and femtoseconds. The fact that different applications require different wavelengths resulted in the development of lasers with many different wavelengths along with tunable lasers. Dye lasers were one of the first to generate tunable radiation, but soon the Ti:sapphire laser emerged as an unrivalled laser source. Semiconductor technology has now resulted in the demonstration of tunable VECSEL laser systems that perhaps challenge Ti:sapphire in versatility. Lasers in the visible region are most often built using nonlinear conversion techniques like second harmonic generation and sum frequency mixing with infrared lasers. With the increase of applications over time, there are many that are constrained by the spectral and temporal characteristics of available commercial lasers. For example, the biophotonics area, with applications in two-photon microscopy and molecular uncaging faces challenges due to the lack of inexpensive laser sources in the visible range. This highlights the importance of developing new laser sources which can access different wavelengths and extend the wavelength reach of existing laser sources. This thesis explores the possibility of wavelength extension and pulse compression by the use of Raman laser technology, by employing the synchronous pumping scheme using diamond and lithium niobate crystals. We report Raman lasers which extend the wavelength reach of a continuous-wave mode-locked picosecond laser. Diamond and lithium niobate have their own unique properties resulting in three different laser systems. The diamond makes an efficient first Stokes and second Stokes laser with a simple cavity design and pulse compression. The lithium niobate crystal resulted in a multiwavelength ultrafast laser generating four wavelengths which were switchable and controllable. We also report a lithium niobate ultrafast Raman laser that generated terahertz waves, using Raman shifting to produce a cavity-enhanced Stokes field to drive THz output using polarition scattering.