Abstract
We propose an efficient approach to improve few-cycle soliton compression with cascaded quadratic nonlinearities by using an engineered multi-section structure of the nonlinear crystal. By exploiting engineering of the cascaded quadratic nonlinearities, in each section soliton compression with a low effective order is realized, and high-quality few-cycle pulses with large compression factors are feasible. Each subsequent section is designed so that the compressed pulse exiting the previous section experiences an overall effective self-defocusing cubic nonlinearity corresponding to a modest soliton order, which is kept larger than unity to ensure further compression. This is done by increasing the cascaded quadratic nonlinearity in the new section with an engineered reduced residual phase mismatch. The low soliton orders in each section ensure excellent pulse quality and high efficiency. Numerical results show that compressed pulses with less than three-cycle duration can be achieved even when the compression factor is very large, and in contrast to standard soliton compression, these compressed pulses have minimal pedestal and high quality factor.
Highlights
High-energy pulsed lasers by employing chirped-pulse-amplification (CPA) technique are developed rapidly both in bulk solid-state and fiber amplifiers
We propose an efficient approach to improve few-cycle soliton compression with cascaded quadratic nonlinearities by using an engineered multi-section structure of the nonlinear crystal
We proposed a new scheme for compressing longer >> 100 fs pulses through a soliton effect to few-cycle duration with high quality
Summary
High-energy pulsed lasers by employing chirped-pulse-amplification (CPA) technique are developed rapidly both in bulk solid-state and fiber amplifiers. The basic idea is that each section is designed to make the effective soliton order Neff > 1 by adjusting the residual (or QPM) phase mismatch, and so that at the exit of each section soliton compression is achieved Such a compressed soliton will at this stage be in balance, so no further compression occurs unless we change the conditions, which is exactly what we propose. Equation (3) shows that with cascaded SHG, solitons can be excited in much the same way as in a Kerr medium [13]: In order for few-cycle pulse compression to occur based on phasemismatched SHG, an effective self-defocusing nonlinearity Neff > 1 with normal dispersion is required. It is a GVM-induced contribution, which acts in a similar way as self-steepening [15]
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