Novel comb sources and mode locking physics

In a mode locked laser, the relative phase between many longitudinal modes is locked in the lasing cavity, leading to the emission of short, coherent pulsess. Nowadays, Ti:Sapphire mode locked lasers produce pulses in the femtosecond scale, exploiting the nonlinear Kerr lens inside the active gain medium to enforce mode locking. The emitted coherent pulse train is represented in the frequency domainby an equi-spaced,phase related frequency comb spreading over a broad spectrum.

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Four-wave mixing and CARS

We investigate the unique two-photon correlation properties of broadband four wave mixing and their applications for coherent Raman spectroscopy and microscopy. In the nonlinear process of four wave mixing a pair of optical frequencies , (pump) are converted to another pair of frequencies , (signal and idler) such that . Quantum mechanically, this process converts a pair of pump photons to a pair of signal-idler photons, which are correlated in energy-time, similar (with very important differences) to entangled photon pairs generated by parametric down conversion.

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Ultra broadband entangled photon pairs

The process of broadband spontaneous parametric down conversion produces photon pairs that are highly entangled in time-energy. The strong correlations of down converted light introduce a whole range of unusual phenomena observed in our research. We observe a classically inexplicable linear dependence of nonlinear sum frequency generation on input flux, when performed with down-converted light. We also demonstrate quantum interference between photon pairs generated at different crystals, allowing interferometric measurement of the two-photon wave function.

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Semiconductor based, mode locked lasers

Developing mode locked lasers based on semiconductor gain media is a long-standing objective in laser research. A major hurdle for the realization of ultra-short pulses in such lasers is the short excited state lifetime in semiconductors (a few nanoseconds), which prevents gain accumulation in the medium for long periods. Thus, most mode locked semiconductor lasers to date operate with very high repetition rates (few - tens of GHz), and low pulse energies.

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A coherent Raman oscillator pumped by a frequency comb

Research focuses on producing coherent Raman oscillation in di-atomic Alkali dimers (Li2, K2, Rb2) gas, by placing the gas in a matched optical cavity, and pumped by a matched frequency comb." As opposed to parametric oscillations and standard lasers, the crossing lasing threshold is possible due to coherent dynamics of the excited vibrational wave packet induced by the pump. Whereas in lasers, the pump is essentially incoherent, and in parametric oscillators, the coherence originates in the pump itself, and this signature is imprinted in the emitted signal/idler fields.

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