8/3/2019 Jyhpyng Wang et al- Application of Laser-Fabricated Plasma Structures in X-Ray Lasers and Plasma Nonlinear Optics

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Application of Laser-Fabricated Plasma Structures in X-Ray

Lasers and Plasma Nonlinear Optics

Jyhpyng Wang1,2,3

, Szu-yuan Chen1,3

, Jiunn-Yuan Lin4, and Hsu-Hsin Chu

3

1Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan2Department of Physics, National Taiwan University, Taipei, Taiwan

3Department of Physics, National Central University, Jhongli, Taiwan

4Department of Physics, National Chung-Cheng University, Min-Hsiung, Taiwan

corresponding author: jwang@ltl.iams.sinica.edu.tw

For the development of soft x-ray lasers and plasma nonlinear optics using femtosecond high-intensity

lasers, we fabricated real-time programmable transient plasma structures to gain fine control on

laser-plasma interaction. Single-shot fabrication of arbitrary gas/plasma structures was demonstrated,

which makes possible on-line adaptive feedback optimization of high-field plasma devices [1]. The

transient plasma structures are created by heating the plasma locally with machining pulses using the

ignitor-heater scheme. The locally heated plasma expands to produce a transient density profile

controlled by the intensity profiles of the machining beams. Plasma gratings with variable period andduty cycle were fabricated by modulating the intensity profile of a transverse machining beam with a

liquid-crystal spatial light modulator, and plasma waveguides were fabricated by reducing the on-axis

plasma density and increasing the off-axis plasma density in a long line-focus produced by an axicon

lens.

In soft x-ray lasers we fabricated a 1-cm long transient plasma waveguide in a gas jet to enhance soft

x-ray lasing of Ni-like Kr at 32.8 nm. By suppressing the diffraction of the x-ray laser pump pulse, the

plasma waveguide increases the output energy by 400 folds to 480 nJ and decreases the divergence

angle by 3 folds to 5.6 mrad. Both the dependences on atom density and on pump energy indicate that

the laser has reached saturation [2]. Since the x-ray lasing is pumped by optical field ionization, the

pump pulse will increase the on-axis plasma density significantly. Thus a major concern was how to

prevent the pump pulse from erasing the waveguide. We found that although the pump pulse increases

the on-axis plasma density, it also produces about the same increase of off-axis plasma density because

the atom density is much higher in the off-axis region. As a result the plasma waveguide is not

compromised by the pump pulse. This is how a dramatic enhancement of x-ray lasing efficiency is

achieved.

In plasma nonlinear optics we fabricated periodic plasma structures to achieve quasi-phase matching

for relativistic harmonic generation. Relativistic third harmonic generation was enhanced by 50 folds.

Resonant dependence of harmonic intensity on plasma density and density modulation parameters

shows the distinct characteristic of quasi-phase matching [3]. We have also fabricated plasma

waveguides to serve as a platform for Raman backward amplification of femtosecond pulses. Through

the interaction with plasma waves, Raman backward amplification can transfer energy from a longpulse to a short pulse, thereby holds the promise of circumventing the fundamental limitation imposed

by material breakdown in femtosecond solid-state laser amplifiers. By using the plasma waveguide to

greatly increase the interaction length, we have achieved a gain of 910 in such plasma amplifiers.

The series of experiments we carried out shows that by controlling the plasma structure with optical

fabrication methods, laser-plasma interaction can be engineered to greatly enrich the frontier of

high-field physics.

References

[1] M.-W. Lin et al., Phys. Plasmas 13, 110701 (2006).

[2] M.-C. Chou et al., Phys. Rev. Lett. 99, 063904 (2007).

[3] C.-C. Kuo et al., Phys. Rev. Lett. 98, 033901 (2007).