Generation Of Few-cycle Laser Pulses Research Articles

Spectral tuning of a broadband optical pulse via stimulated Raman scattering of a prealigned molecule

The nonlinear spectral broadening of a near-infrared laser pulse propagating through pre-aligned molecules is investigated experimentally in a pump-probe scheme. The spectral shift of over 100 nm as well as spectral shaping is achieved via tuning the experimental conditions such as pump-probe delay, gas pressure, and pulse energy. Numerical simulation based on the nonlinear Schr\"odinger equation shows that the experimentally observed spectral tuning is due to the competition between different nonlinear effects, i.e., stimulated Raman scattering, the Kerr effect, and molecular alignment. Adjusting the pump-probe delay properly can decouple different nonlinear processes and allows for spectral tuning in a controlled way. This scheme is demonstrated to be attractive for the generation of few-cycle laser pulses with a frequency-tunable spectrum, broadband pulse shaping, and many strong field applications in the visible range.

Generation of few-cycle laser pulses at 2 μm with passively stabilized carrier-envelope phase characterized by f-3f interferometry

We report on generation and characterization of few-cycle laser pulses with the central wavelength of 2 μm at repetition rate of 50 kHz. The source is based on noncollinear parametric amplification and difference frequency generation leading to passively stabilized carrier-envelope phase (CEP). CEP is characterized using f-3f technique based on spectral interference between the fundamental spectrum broadened via self-phase modulation and the third harmonics, which are both generated by tight focusing of the pulses to gallium gadolinium garnet (GGG) crystal. We demonstrate the capability of this technique for CEP measurement and long-term stabilization. Further we show that the pulses can be compressed to a duration of 1.7 optical cycles after spectral broadening in the GGG crystal.

Few-cycle localized plasmon oscillations

The generation of few-cycle laser pulses proved to be a key enabling technology in strong-field physics and ultrafast science. The question naturally arises whether one can induce few-cycle localized plasmon oscillations in optical near-fields. Here, we perform a comparative study of different plasmonic nanoresonators illuminated by few-cycle pulses. We analyze the number of cycles (NOC) of the plasmonic field, the near-field enhancement (NFE) as well as the figure of merit NFE/NOC. The pulse length dependence of these quantities is also investigated. Throughout the inspected pulse-length interval silica-gold and silica-silver core–shell monomers have the potential to preserve the NOC of the incoming pulse, silver bow-ties result in the highest NFE, whereas gold core–shell dimers have the highest NFE/NOC. Based on the analysis, silver bow-ties, gold core–shell and silver nanorod dimers proved to be the most suitable for few-cycle near-field amplification.

Generation of few-cycle laser pulses with high temporal contrast via nonlinear elliptical polarisation rotation in a hollow fibre compressor

We report on the simultaneous temporal filtering and compression of 30 fs laser pulses down to 5 fs duration via nonlinear elliptical polarization rotation (NER) in a stretched flexible hollow fibre compressor. Both the achieved 2-cycle pulse duration and the internal conversion efficiency of ∼47% are solely limited by the applied fibre geometry. Our investigations show that precise control of the NER process could help significantly improve the temporal fidelity of high-energy hollow fibre compression schemes.

Generation of few-cycle laser pulses by coherent synthesis based on a femtosecond Yb-doped fiber laser amplification system

We demonstrate a coherent synthesis system based on femtosecond Yb-doped fiber laser technology. The output pulse of the amplification system is divided into two replicas and seeded into photonic crystal fibers of two parallel branches for nonlinear pulse compression. Because of the different nonlinear dynamics in the photonic crystal fibers, the compressed pulses show different spectra, which can be spliced to form a broad coherent spectrum. The integrated timing jitter between the pulses of two branches is less than one tenth of an optical cycle. By coherently synthesizing pulses from these two branches, 8 fs few-cycle pulses are produced.

Generation of few-cycle laser pulses: Comparison between atomic and molecular gases in a hollow-core fiber**Project supported by the National Natural Science Foundation of China (Grant Nos. 11204328, 61221064, 61078037, 11127901, 11134010, and 61205208), the National Basic Research Program of China (Grant No. 2011CB808101), and the Natural Science Foundation of Shanghai, China (Grant No. 13ZR1414800).

We numerically study the pulse compression approaches based on atomic or molecular gases in a hollow-core fiber. From the perspective of self-phase modulation (SPM), we give the extensive study of the SPM influence on a probe pulse with molecular phase modulation (MPM) effect. By comparing the two compression methods, we summarize their advantages and drawbacks to obtain the few-cycle pulses with micro- or millijoule energies. It is also shown that the double pump-probe approach can be used as a tunable dual-color source by adjusting the time delay between pump and probe pulses to proper values.