Fan Dian-Yuan

Influence of Higher-Order Dispersions and Raman Delayed Response on Modulation Instability in Microstructured Fibres

Modulation instability (MI) in microstructured photonic crystal fibres is studied by using an extended nonlinear Schrodinger equation. The roles of arbitrary higher-order dispersions and Raman delayed response in MI are identified. It is shown that all the odd-order dispersions contribute nothing to MI, whereas all the even-order dispersions not only affect the conventional instability regions but also may lead to the appearance of new MI regions. Raman delayed response makes MI occur in both the normal and anomalous dispersive regimes and exerts different influences on the Stokes and anti-Stokes components to some extent.

A Compact Nanosecond-Pulse Shaping System Based on Pulse Stacking in Fibres

We demonstrate a compact pulse shaping system based on temporal stacking of pulses in fibres, by which synchronized pulses of ultrashort and nanosecond lasers can be obtained. The system may generate shape-controllable pulses with a fast rise time and high-resolution within a time window of ~2.2?ns by adjusting variable optical attenuators in the 32 fibre channels independently. With the help of optical amplifiers, the system delivers mJ-level pulses with a signal-to-noise ratio of ~35?dB.

Suppression of FM-to-AM Conversion in Broadband Third-Harmonic Generation of Nd:Glass Laser

Frequency modulation to amplitude modulation (FM-to-AM) conversion is important for controlling temporal shapes of high-power Nd:glass lasers in the application of fusion ignition. To suppress this FM-to-AM conversion effect in the process of broadband third-harmonic generation of Nd:glass laser, we report an efficient frequency-tripling scheme based on mixing narrowband and broadband pulses. Numerical results show that the FM-to-AM conversion in frequency conversion process can be suppressed effectively. For a required third-harmonic bandwidth of 1 THz, the defined relative modulation α in pulse intensity is as large as 180% in the conventional baseline design, while it will be reduced to only about 20% by using our proposed scheme.

A Phase-Controlled Optical Parametric Amplifier Pumped by Two Phase-Distorted Laser Beams

We theoretically study the phase characteristic of optical parametric amplification (OPA) or chirped pulse OPA (OPCPA) pumped by two phase-distorted laser beams. In the two-beam-pumped optical parametric amplification (TBOPA), due to spatial walk-off, both of the pump phase distortions will be partly transferred to signal in a single crystal so as to degrade the signal beam-quality, which will be more serious in high-energy OPCPA. An OPA configuration with a walkoff-compensated crystal pair is demonstrated for reducing the signal phase distortion experienced in the first stage and ensuring the signal phase independent of two pump phase distortions through the second crystal, hence maintaining the signal beam-quality. Such a TBOPA is similar to the conventional quantum laser amplifier by means of eliminating its sensitivity to the phase and number of the pump beams.

Femtosecond Optical Parametric Amplifier for Petawatt Nd:Glass Lasers

We study a femtosecond Ti:sapphire laser pumped optical parametric amplifier (OPA) at 1053 nm. The OPA generates stable signal pulses with duration smaller than 100 fs, wavelength drift smaller than 0.5 nm, and pulse-to-pulse fluctuation of about ±4%, by employing an external seeder. In a terawatt laser pumped large-aperture LiNbO3 OPA, pulse energy at signal has been scaled up to 4 mJ. This mJ-class femtosecond OPA at 1053 nm presents a feasible alternative to optical parametric chirped-pulse amplification, and is ready to be applied to petawatt lasers.

A Formula of Propagating Beams Driven by Few-Cycle Gaussian Pulse in Dispersive Media

A formula is developed to describe the propagation of beams driven by few-cycle Gaussian pulse in a media with group velocity dispersion (GVD). With the method, the spatiotemporal evolution of the pulsed beam can be straightforwardly quantified as long as the monochromatic beam solutions in free space, which have been widely investigated in previous works, are known. The method makes it possible to analytically deal with the few-cycle pulsed beams with transverse profiles other than the Gaussian one, which is, to our knowledge, the one mainly investigated previously, in GVD media.

Widely tunable dual-pump parametric amplifiers with photonic crystal fibres

This paper theoretically studies the double-pumped fibre-optical parametric amplifiers (FOPAs) in photonic crystal fibres. Two distinct working regimes of FOPAs are researched, which depend on the dispersion at the central wavelength of the two pumps. Extremely broad tuning range can be obtained when the central pump wavelength is in the normal dispersion regime and is insensitive to the wavelength separation between the two pumps, while the tuning range is narrow in the anomalous dispersion regime and can be significantly enhanced by increasing the wavelength separation. Impacts of higher-order dispersions and temporal walk-off on the gain spectra are also discussed.

Influence of spatiotemporal coupling on the capture-and-acceleration-scenario vacuum electron acceleration by ultrashort pulsed laser beam

This paper investigates the properties of the ultrashort pulsed beam aimed to the capture-and-acceleration-scenario (CAS) vacuum electron acceleration. The result shows that the spatiotemporal distribution of the phase velocity, the longitudinal component of the electric field and the acceleration quality factor are qualitatively similar to that of the continuous-wave Gaussian beam, and are slightly influenced by the spatiotemporal coupling of the ultrashort pulsed beam. When the pulse is compressed to an ultrashort one in which the pulse duration TFWHM<5T0, the variation of the maximum net energy gain due to the carrier-envelope phase is a crucial disadvantage in the CAS acceleration process.

Stimulated Raman Scattering of a Modulated Laser Beam in Air: a Perturbation Approach

Stimulated Raman scattering (SRS) of a third-harmonic beam of a high-power laser in air is analysed by using a perturbation approach. It is found that intensity modulations of the third-harmonic beam, resulting from the surface ripple of nonlinear crystal, can be significantly enhanced due to SRS, and the gain of instability increases with the spatial period of modulation. Numerical simulations based on the nonlinear coupled-wave equations verify the validity of the perturbation approach.

Generation of Ultrashort Light Bullets in Dispersive Kerr Media Using the Fourth-Order Dispersion-Dependent Spatiotemporal Instability

A new method for generation of a train of ultrashort pulses or a sequence of ultrashort light bullets is proposed. This method is based on the fourth-order dispersion-dependent spatiotemporal instability in dispersive Kerr media. The repetition-rate of the generated bullets can be made quite large by increasing the corresponding spatial modulation frequency locating in the new instability region resulted from fourth-order dispersion.