Jianqin Deng

Multiple hot images from an obscuration in an intense laser beam through cascaded Kerr medium disks

We present a theoretical investigation on the formation of hot images in an intense laser beam through cascaded Kerr medium disks, to disclose the distribution and intensity of hot images in high-power disk amplifiers. It is shown that multiple hot images from an obscuration may be formed, instead of one hot image as reported previously in the literature. This gives a clear explanation for the curious damage pattern of hot images, namely, damage sites appearing on alternating optics in periodic trains. Further analysis demonstrates that the distribution and intensity of hot images depend closely on the number of Kerr medium disks, the distance from the obscuration to the front of the first disk downstream, the space between two neighboring disks, and the thickness and B integral of each disk. Moreover, we take two cascaded Kerr medium disks for example to detail multiple hot images from an obscuration and confirm the theoretical results by numerical simulations.

Engineering deceleration and acceleration of soliton emitted from Airy pulse with quadratic phase modulation in optical fibers without high-order effects.

Soliton propagation direction can be engineered in optical fibers in the presence of high-order effects (HOEs). It is well known that Raman effects can decelerate the soliton. Here we investigate the manipulation of the deceleration or acceleration of soliton emitted from Airy pulse whose spectrum is imposed an initial quadratic phase modulation (QPM) in optical fibers in the absence of HOEs. We show that, under the action of the anomalous second-order dispersion (SOD) and Kerr nonlinearity, Airy pulse with QPM is able to emit soliton with acceleration or deceleration depending on whether the QPM is negative or positive, and at a rate that is determined by the magnitude of QPM. The reason is that the acceleration behaviors of incident Airy pulse is altered depending on whether SOD and QPM have the same or opposite signs. Our study shows the possibility of controlling and manipulating the soliton propagation and interaction in optical fibers without HOEs, by purposely choosing appropriate QPM parameter of an Airy pulse.

Role of chirp in spatiotemporal modulation instability of broadband pulsed laser

We report on the theoretical derivation and experimental demonstration of the influence of chirp on the spatiotemporal modulation instability in a nonlinear Kerr medium. Based on a derived (3 + 1)-dimensional nonlinear Schrodinger equation for chirped laser pulse propagation, we obtain the expression for the instability gain spectrum of a chirped laser pulse by using a standard linear stability analysis. It is shown that the pulse chirp does not affect the instability region and the fastest growth frequency. In the experiment, we observe the nonlinear growth of spatial stripes with different modulation frequency due to the small-scale self-focusing. We also obtain the gain spectra of the laser pulses with different values of pulse chirp. It is found that, for the condition that the contributions of nonlinearity (Nnl) are equal, the experimental results are in agreement with the theoretical predictions.

Discriminating the role of Raman effects in the propagation of decelerating and accelerating Airy pulses by time–frequency analysis

We present a numerical study of the propagation dynamics of accelerating and decelerating truncated Airy pulses (TAPs) in the anomalous dispersion region of optical fibres, with inclusion of the Raman scattering effects, by analysing their cross-correlation frequency resolved optical gating traces. We identify the differences between the evolution dynamics of a decelerating and accelerating TAP. It is shown that the main lobe of the pulse is capable of shedding solitons, which are delayed due to the Raman effects. For the decelerating pulse, however, the soliton is dragged from the original pulse and never meets the input oscillatory Airy tail due to the deceleration of both the pulse and the soliton. The rest of the decelerating pulse rebuilds a new Airy waveform with a stronger degree of truncation compared with that of the incident pulse. For the accelerating TAP, the soliton collides continuously with the tail of the pulse and thus gains further energy by means of their nonlinear interaction. As a consequence, the remaining pulse cannot develop a new Airy waveform. In addition, under the same conditions, the Raman-induced frequency shift of the accelerating TAP is much larger compared with that of the decelerating one.

Experimental measured for the effects of broadband pulse on the B-integral of small-scale self-focusing

It is well known that small-scale self-focusing is one of the major factors to restrict the capability and efficiency of high-power solid-state laser driver. B-integral is used to measure the severity extent of small-scale self-focusing and the typical value of B-integral is less than 1.8 in narrow band high power laser by NIF. We experimentally obtained the relationship of B-integral with spatial contrast for broadband pulse in case of active modulation and random noise modulation, and found that the growth of contrast is still very slow after B-integral up to 1.8 for 12 nm ultrashort pulse laser. So we can consider that the broadband laser is able to unloosen B-Integral criterion and then improve the system loading.

Control of high power laser in nonlinear media by lens-focusing and beam self-focusing

In this paper, we firstly preliminary analyzed how to control the collapse position of beam when intensity and beam waist have been varied by the laser self-focusing in nonlinear media and lens-focusing. We obtain the relations of the focusing position with input power and focal length of lens. The length of focusing is inversely proportional to the input power and directly proportional to focal length of lens. Secondly, Based on the nonlinear propagation equation and split-step Fourier method, we investigate how to control the focal distance and beam quality of high-power laser at focusing spot in nonlinear media. We can control the focusing spot at any position by changed power and lens. The numerical simulations is good consistent with theoretical analysis.