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Two-dimensional electronic spectroscopy is a kind of nonlinear optical spectroscopy with both high time resolution and high frequency resolution. It can be used to observe the complex dynamics of a condensed molecular system. Meanwhile it is a very powerful tool to study the coherence between the electronic states or electronic and vibration states. In 2007, Flemming's group reported the long-lived quantum coherence observed in the energy transfer process in the light-harvesting antenna protein complex Fenna-Matthews-Olson at 77 K by means of two-dimensional electronic spectroscopy. Though it has been proved not to arise from the pure electronic coherence later, this discovery has greatly stimulated the exploration of the coherent energy transfer pathways possibly existing in the natural and artificial photosynthetic systems, and this is still a very active area nowadays. Here in this paper we briefly review the principle and set-up of the two-dimensional electronic spectroscopy, and also some of its applications in investigating coherent energy transfer in the photosynthetic and artificial systems, aiming to bring this novel spectroscopic tool into a wider application.

We design and experimentally demonstrate some negative dispersion mirrors with optimized Gires-Tournois interferometers. The mirror structure is composed of 38 alternating Ta2O5 and SiO2 layers and could be regarded as two sections: high-reflectivity section consisting of a series of quarter-wavelength optical thickness stacks and negative-dispersion section consisting of only 13 layers. The designed mirrors exhibit the expected performance. These mirrors were fabricated by using ion beam sputtering. By adopting such mirrors, dispersion of a mode-locked femtosecond Ti:sapphire laser has been compensated for mostly. With two series of the mirrors, 32 fs and 15 fs pulses have been obtained respectively.

The negative nonlinear index of a semiconductor saturable absorber mirror (SESAM) was investigated by using the reflection Z-scan technique. This is an experimental demonstration, for the first time to our knowledge, that the SESAM possesses comparable negative nonlinear index n2 = ?2.35?10?10?esu, which may have important implications in design and alignment of Kerr-lens mode-locking based on the self-focusing effect.

Birefringent microstructure fibers are shown to allow efficient gereration of anti-Stokes line emission as a result of four-wave-mixing in higher mode by using unamplified femtosecond Ti:sapphire laser pulses.Intense blue-shifted lines with different central wavelength were generated in the high-delta (i.e.high-air filling in the cladding) microstructure fiber with axis sizes 50 and 46 μm by femtosecond laser pulses with 35-fs in duration,820nm in central wavelength and 4nJ in energy per pulse.The experimental result shows that phase-matched four-wa ve mixing in higher-order modes of microstructure fibers allows unprecedentedly high efficiencies of anti-Stokes frequency conversion to be achieved for subnano joule femtosecond laser pulses.The dependence factor of the four waves mixing in birefringent microstructure fiber is compared and analyzed.Good agreement betwe en the theory and experiment is achieved.

In this letter, we systematically investigated the temporal and spectral characteristic of ultra-broad band Ti:sapphire oscillator in femtosecond regime. Pulse formation in temporal regime was observed while the spectral shape evolved fro m hyperbolic secant shape into multi-peak one and the bandwidth increased from 40 to 180nm. Experimental results showed that pulse shortening mainly occurred n ot at its bottom part but at its central section while the spectrum was broadene d, and at the same time the relative energy at the bottom part increased.

The five-mirror laser cavity containing a semiconductor saturable absorber mirror (SESAM) with negative Kerr effect is theoretically analyzed for the first time. It shows that, compared with the cavity without a SESAM, the upper stable range of the resonator expands obviously after the introduction of SESAM. This indicates that the work point for self-starting can be more close to the edge of the stable range of the CW state, and then get higher nonlinear effect. This shows that the negative Kerr effect of the SESAM can contribute to the self-starting of the modelocked laser besides the saturable absorption mechanism.

A Ti: sapphire oscillator emitting an octavespanning spectrum that ra nges from 460nm to 1000nm is demonstrated. To our knowledge, it is the first tim e that a supercontinuum extending beyond 500nm in the blue end is generated from a femtosecond oscillator. The selfQswitched and selfmodelocked Ti: sapphi re oscillator uses chirped mirrors and a prism pair for dispersion compensation. Th ese results will make the measurement of carrierenvelope offset frequency simp ler and improve the stability of optical frequency metrology at the same time.

An experimental study of supercontinuum generation in a photonic crystal fiber with zero dispersion wavelength 780?nm by femtosecond laser and its dependence factor is presented. Supercontinuum light with a spectrum more than one octave broad (500-1100?nm) was generated in a photonic crystalfiber by femtosecond pulses from a selfstarting, selfmode locked Ti:sapphire oscillator running at center wavelength of 810-840?nm. Different supercontinuums were generated by the 35?fs pulses with different power, central wavelength, prechirp, and the continuous noise in the femtosecond pulses. Some reasonable analysis result is obtained from the comparisons of the experimental results, and the mechanism of the supercontinuum generation is analyzed.

A random distributed microstructure fiber in which strong asymmetry was introduced around a puresilica core was reported. Femtosecond laser pulses with duration of 35?fs from a Ti:sapphire laser oscillator were coupled into this fiber, and then periodic color rings were observed from the side of the fiber when the supercontinuum light propagated along the fiber. We attributed this phenomenon to the polarization beating of the supercontinuum light in this highly birefringent microstructure fiber. Measurement showed that the fiber had a beat length of approximately 1?mm at a central wavelength of 600?nm, which is in good agreement with the result of calculation. A new method is proposed to measure the beat length directly in a highly birefringent microstructure fiber.