Investigation on the influences of linear chirp with different input pulse intensities on BaF2 cross-polarized wave generation

Li, Gang; Liu, Hongjie; Liu, Feng; Xian-Lun, Wen; Ying-Ling, He; Zhang, Faqiang; Dai, Zenghai

doi:10.7498/aps.64.020602

Acta Phys. Sin.

2015

DOI: 10.7498/aps.64.020602

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Investigation on the influences of linear chirp with different input pulse intensities on BaF2 cross-polarized wave generation

Gang Li¹,

Hongjie Liu²,

Feng Liu³

et al.

Abstract: Cross-polarized wave (XPW) generation based on BaF2 crystal is one of the most important tools in improving the contrast of ultra-intense femtosecond laser pulses at present. In this paper, the influences of linear chirp with different input pulse intensities on BaF2 XPW generation, including conversion efficiency, spectrum broadening, and pulse duration reduction are in detail simulated and discussed. Especially, the influence of linear chirp on spectrum broadening is comparatively investigated under unsatura… Show more

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Cited by 4 publications

References 25 publications

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Simulation of a chirped femtosecond relativistic laser pulse interaction with underdense plasma by using a hydrodynamic approach

Zhu

et al. 2019

Contributions to Plasma Physics

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A chirped laser pulse indicates that the laser frequency changes over the duration of the pulse: a positively (negatively) chirped pulse implies that the laser frequency increases (decreases) with time. In this paper, we use a simplified, fully relativistic hydrodynamic approach to simulate the influence of chirp on the propagation of a femtosecond relativistic laser pulse in underdense plasma. Based on this simplified cold-fluid model, the influence of chirp on the main dynamics of the laser pulse, such as self-steepening, red-shift in the leading edge, variation of the frequency chirp, and the generated wakefields can be studied self-consistently. The simulation results show that a pulse with a positive chirp results in a larger increment in the intensity parameter a 0 when propagating a certain distance into an underdense plasma compared with an un-chirped and a negatively chirped pulse, which is largely because of a much greater forward shift of the peak amplitude and more severe pulse self-steepening effect due to the frequency red-shift at the leading edge when exciting a plasma wave. The ponderomotive force, which relates to the first-order differential of the laser pulse intensity envelope, is expected to be stronger for a positively chirped pulse because of its steeper leading edge and larger intensity parameter a 0 .As a result, the wakefield driven by the positively chirped laser pulse is more intense than that driven by an un-chirped and a negatively chirped laser pulse, which is confirmed by our self-consistent hydrodynamic simulation. K E Y W O R D Schirp, femtosecond relativistic laser, plasma, wakefield INTRODUCTIONUsing the chirped pulse amplification (CPA) technique, ultrashort-pulse laser sources with durations on the femtosecond time scale can produce multi-terawatt and even petawatt power. [1][2][3] These laser pulses can be focused to intensities well above 10 18 W/cm 2 , [4] from which an electron will acquire a quiver velocity approaching the speed of light; that is, the electron motion in the laser fields becomes highly relativistic and non-linear. Thus, these laser pulses are called relativistic femtosecond laser pulses and have great applications in high energy density science, such as energetic electron acceleration, [5] ion acceleration, [6] attosecond pulses generation, [7,8] positron beams for laboratory astrophysics, [9] and so on. These applications require long laser

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Simulation of a chirped femtosecond relativistic laser pulse interaction with underdense plasma by using a hydrodynamic approach

Zhu

et al. 2019

Contributions to Plasma Physics

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Influences of quadratic spectral phase on characteristics of two crystal cross-polarized generation with femtosecond pulses

Yi-Xing¹,

Rong-Feng²,

Yan-Ying³

et al. 2017

Acta Phys. Sin.

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The rapid developments of ultra-intense and ultra-short laser offer the possibility to study laser driven ion acceleration with using solid density target. However, the prepulse and amplified spontaneous emission generated in the amplification can create preplasma at the target front by heating, melting and evaporating a portion of a solid density. The main pulse then interacts with the preplasma, which would be harmful to laser ion acceleration. Therefore, many methods have been developed to enhance the temporal contrast of high power laser system, such as saturable absorber, cross polarized wave generation (XPW) and plasma mirror. With many advantages, such as high conversion efficiency, introducing neither spatial nor spectral distortions, and easy setup compared with other mechanisms, XPW has been used to clean the femtosecond laser system. Besides that, the spectrum of the XPW pulse could be broadened by 3 times under the best condition compared with the initial spectrum. It can solve the spectrum narrowing problem during the laser amplification to obtain ultra-short femtosecond laser pulse. Here, we experimentally investigate the output power, spectrum bandwidth and center wavelength shift of the generated cross-polarized wave according to the input pulse quadratic spectral phase. The femtosecond laser pulse in compact laser plasma accelerator system at Peking University is used to investigate the role of quadratic spectral phase in characterizing the two crystal cross-polarized generation. The Ti:Sapphire-based laser system has a central wavelength of 798 nm and bandwidth of 35.5 nm which allows the pulse to be compressed down to 40 fs duration (FWHM). Typical the input pulse energy of XPW is 150 upJ and the laser system operates well at 1 kHz repetition rate. The quadratic spectral phase can be increased by changing the position of compressor grating. The conversion efficiency, spectrum bandwidth and the central wavelength shift by changing the quadratic spectral phase are measured. The conversion efficiency is 17% when quadratic spectral phase 2=0, and decreases as quadratic spectral phase increases. The rapid decrease is caused by negative quadratic spectral phase. The spectrum bandwidth is 62 nm under the optimum condition, and the broadening effect exists when quadratic spectral phase is in a range of -280 fs2 2 1400 fs2. It is slowly blue-shifted when 20 and stays at 772 nm when 21000 fs2. It starts to be red-shifted when 20 and stays at 806 nm finally. In conclusion, with the increase of quadratic spectral phase, we observe the effects of conversion efficiency and spectrum bandwidth and the shift of central wavelength. Moreover, the influences of positive and negative quadratic spectral phase on characteristics of XPW are different. Our result shows that the negative quadratic spectral phaseis more effective at reducing the conversion efficiency and spectrum bandwidth than the positive one.

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Influence of linear chirp on the output characteristics of cross polarized wave with saturated power density

Shuang¹,

Wang²,

Wang³

et al. 2017

Acta Phys. Sin.

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Ultra-short and ultra-intense laser is one of the hottest research spot of laser technology and strong field physics, due to its challenging and the frontier application research. As the key specification of ultrafast ultrahigh intensity laser pulse, the contrast ratio is very influential on the effect of laser-matter interaction. To perform the laser-matter interaction experiments at a high power level, the contrast is required to be as high as 1010 to prevent preplasma dynamics. To solve these problems, one has proposed many methods to improve the contrast of ultrafast laser, such as using the saturable absorbers, double chirped pulse amplification, plasma mirrors and the cross-polarized wave (XPW) generation. The XPW technology can not only enhance the contrast of the pulse by 3-4 orders of magnitude without introducing any space dispersion, but also extend the output spectrum to support shorter pulse duration. The XPW is a nonlinear filter technique in third-order nonlinear crystal with anisotropic susceptibility. Because of its simple and all-solid-state structure, the XPW technique has become one of the most effective methods to enhance the temporal pulse contrast and deliver shorter pulse duration in the field of high peak-power ultrafast lasers. This method has been used in many large laser facilities under construction or upgrades, such as the Apollon and ELI, the contrast ratio as high as 1010 has been achieved. It is known that the conversion efficiency and spectral characteristics of XPW have a strong dependence on the spatial and temporal magnitudes of the input driving pulse. In our experiment, it is found that the various changes of the driven pulse properties have different influences on the characteristics of XPW pulses. The relationship between the linear dispersion of driven pulse and temporal property of XPW is investigated theoretically. In addition, an experiment on verifying the theory is conducted by taking advantage of a programmable acousto-optic dispersion filter. The experimental results fit well to the theoretical results while some new phenomena emerge when the intensity in the BaF2 crystal reaches a saturation threshold. The spectral broadening capability of XPW becomes stronger and exceeds a theoretical upper limit. The pulse width can also be compressed to shorter than the theoretical limit. It is found that there are significant differences in spectral shape and conversion efficiency between the XPW signals by applying the opposite linear chirps to the driving pulse. A further analysis and theoretical explanation of these new phenomena are also presented.

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Investigation on the influences of linear chirp with different input pulse intensities on BaF2 cross-polarized wave generation

Cited by 4 publications

References 25 publications

Simulation of a chirped femtosecond relativistic laser pulse interaction with underdense plasma by using a hydrodynamic approach

Simulation of a chirped femtosecond relativistic laser pulse interaction with underdense plasma by using a hydrodynamic approach

Influences of quadratic spectral phase on characteristics of two crystal cross-polarized generation with femtosecond pulses

Influence of linear chirp on the output characteristics of cross polarized wave with saturated power density

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