19 January 2012 Congratulations to New ICFO PhD Graduate

Dr. S. Chaitanya Kumar


Thesis Committee

Dr. Chaitanya Kumar graduated with a thesis on Optical Parametric Oscillators. Dr. S. Chaitanya Kumar obtained an MSc in Physics from the Indian Institute of Technology at Guwahati, India. In 2007 he joined ICFO at the Optical Parametric Oscillators group led by ICREA Prof. Majid Ebrahim-Zadeh to work on a project related to optical frequency conversion systems.

Dr. Chaitanya Kumar presented a thesis titled ‘High Power, Fiber-Laser-Pumped Optical Parametric Oscillators from Visible to Mid-Infrared’ supervised by Prof. Ebrahim-Zadeh.

Congratulations!

ABSTRACT

High-power, continuous-wave (cw), mid-infrared (mid-IR) laser sources are of interest for variety of applications such as trace gas detection and remote sensing, which require broad spectral coverage to address the most prominent absorption features of a wide range of molecular species particularly in the mid-IR fingerprint region. On the other hand, surgical applications require high energy sources with unique pulse structure at specific wavelength in the mid-IR ranging from 6-6.5 µm.

Optical parametric oscillators (OPOs) offer potential sources for all the above applications. The output wavelengths of a singly-resonant oscillator (SRO) can be coarsely tuned over wide ranges through the adjustment of the nonlinear crystal temperature, phase-matching angle or, in the case of quasi-phase-matched (QPM) materials, the QPM grating period. The combination of SRO with a tunable pump laser allows the development of uniquely flexible and rapidly tunable class of mid-IR sources.

In this thesis we have demonstrated several mid-IR OPOs in the cw as well as ultrafast picosecond regime pumped by fiber-lasers making them compact and robust.

In the cw regime, we developed a high-power, Yb-fiber-laser pumped mid-IR OPO based on MgO:PPLN spanning 1506-1945 nm in the near-IR and 2304-3615 nm wavelength range in the mid-IR, efficiently addressing the thermal effects by implementing the optimum signal output coupling. Novel materials such a MgO:sPPLT, with better optical and thermal properties for cw mid-IR generation are explored. High-power broadband, cw mid-IR generation is also demonstrated by using the extended phase-matching properties of MgO:PPLN.

Further, we also demonstrated a simple, inexpensive and novel interferometric technique for absolute optimization of output power from a ring optical oscillator. We deployed a picosecond Yb-fiber-laser pumped mid-IR OPO based on MgO:PPLN in ring cavity configuration to demonstrate this proof-of-principle experiment for the first time. The high-energy CSP OPO marked the first demonstration of a compact, high-repetition-rate OPO synchronously pumped by a master oscillator power amplifier system at 1064 nm, generating an millijoule pulses in the 6-6.5 µm spectral range, which is technologically important for surgical applications.

Additionally, we also demonstrated a fiber-based-green source at 532 nm, based on single-pass second harmonic generation (SHG) in MgO:sPPLT, as an alternative pump source for Ti:sapphire laser, pointing towards the future, compact fiber-laser pumped Ti:sapphire lasers. Further efforts to improve the SHG efficiency led to the development of a novel multi-crystal scheme, enabling single-pass SHG efficiency as high as 56%. This generic technique is simple and can be implemented at any wavelength.


THESIS COMMITTEE:

President: Prof. Frans J.M. Harren , Department of Molecular and Laser Physics - Radboud University Nijmegen, the Netherlands.

Secretary: Dr. David Artigas, Associate Professor, UPC - ICFO, Spain.

Member: Prof. Ajoy Kumar Kar, School of Engineering and Physical Sciences, Heriot-Watt University, UK.

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