Laser Pulse Compression in Plasma Density Gradient: Exploring New Progress in EW (Eva) to ZW (Zewa) Lasers
Min Sup Hur and his team adopted an innovative laser pulse compression method in their recent research, using laser pulses to pass through plasma with gradient density to achieve compressed laser pulses. This research demonstrates how laser pulse compression can be achieved with smaller size and higher efficiency [1][2]. They used the self-developed particle simulation code cplPIC for simulation, which adopted standard algorithms including Boris mover and Buneman–Villasenor charge conservation scheme [7].
Experimental results show that the team successfully compressed a pulse of 25 picoseconds and 4 terawatts (more than 100 joules) to 25 femtoseconds and 2 petawatts (about 50 joules), with an efficiency of 35% [5]. This achievement indicates that using millimeter-scale plasma gratings can achieve hundreds of times of pulse compression with almost no energy loss, and is much smaller than the traditional chirped pulse amplification (CPA) system [1][2].
Figure 1. One-dimensional PIC simulation of pulse compression in gradient plasma.
a, Stroboscopic view of incident pulse (red) and reflected pulse (green to blue). On the plasma density curve (gray shading), nl and nh are the critical densities of ωn (the highest frequency at the front of the pulse) and ω (the lowest frequency at the tail of the pulse), respectively.
b, b. Electric field as a function of time by positioning atx = 0.1 mm through the virtual probe. Data are divided into incident (red), compression (blue) and Raman backscattered (RBS, orange, magnification x10).
c, c, compressed pulse width.
d, d. Power spectra of incident (red), RBS (orange, x10 magnification) and compression (blue) pulses.
Traditional CPA technology compensates for the initial chirp by first stretching the pulse to reduce the peak power, then by amplifying it, and finally by compressing the pulse through a dispersive element (such as a grating or prism). Although CPA technology can effectively increase pulse intensity, its complex optical paths and large optical components make the system larger. In addition, the CPA process may introduce some pulse distortion [1][2].
In addition, nonlinear spectrum broadening technology is also a commonly used pulse width compression method. This method increases the spectral width of a laser pulse by propagating it in a nonlinear medium, and then time-compresses the broadened pulse through a dispersive element, such as a prism or grating. This method can achieve extremely short pulses, but may be accompanied by certain pulse distortion and energy loss.
Figure 2. Schematic structural diagram of CPA [6]
The laser pulse compression method in plasma density gradient does not achieve pulse width compression by directly compensating dispersion. The working principle of this method is different from traditional dispersion compensation techniques such as chirped pulse amplification (CPA) or nonlinear spectral broadening techniques. In the plasma density gradient compression method, laser pulses are compressed as they pass through a plasma with gradient density. This method uses the characteristics of the plasma to change the temporal structure of the laser pulse, thereby achieving pulse compression. As a laser pulse propagates through a plasma, its different frequency portions experience different optical path lengths due to changes in the density of the plasma. This effect causes the pulse to be compressed in time, resulting in a shorter pulse.
Figure
3. Concept of plasma pulse compression. Laser pulse compressor based on density gradient plasma, in which long-duration, high-energy, negative-frequency chirped laser pulses are reflected from an over-dense plasma plate of increasing density. The high-frequency components at the front of the pulse and the low-frequency components at the back of the pulse are reflected at different locations, resulting in laser pulse compression. [7]
The plasma density gradient compression method provides a pulse compression mechanism that is different from dispersion compensation. Its main advantage is that it can achieve high-efficiency pulse compression without the need for complex optical systems. This technology significantly reduces the physical size of the system. It also maintains the spectral characteristics of the original pulse during the compression process, helping to achieve higher powers [1][2][3][4][5]. Especially suitable for high power laser applications.
Overall, the plasma density gradient compression method has obvious advantages in terms of volume, efficiency and pulse quality maintenance, and is especially suitable for applications requiring compact high-power laser systems. Traditional CPA technology and nonlinear spectrum broadening technology still have irreplaceable value in specific application scenarios. By understanding the different pulse compression techniques, we can better select the appropriate pulse compression method based on specific scientific and industrial needs. As these technologies continue to develop and improve, they will further push the boundaries of laser technology and lay the foundation for future innovative applications!
References
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2. Chang, J.-C., Chang, S., Wu, Y.-C., & Chang, C.-Y. (2021). [Fast and direct optical dispersion estimation for ultrafast laser pulse compression]The Review of scientific instruments*.
3. Balakin, A., Skobelev, S., Andrianov, A., Kalinin, N., & Litvak, A. (2019). [Laser pulse compression up to few-cycle durations in multicore fiber] *Optics Letters*.
4. Alessi, D., Nguyen, H. T., Britten, J., Rosso, P., & Haefner, C. (2018). [Low-dispersion low-loss dielectric gratings for efficient ultrafast laser pulse compression at high average powers]. *Optics & Laser Technology*.
5. Shi, Y., Qin, H., & Fisch, N. (2016). [Laser-pulse compression using magnetized plasmas]*Physical review. E*.
6. Backus S，Durfee C G，Murnane M M et al. Rev. of Sci. Instru., 1998，69：1207
7. Min Sup Hur, Bernhard Ersfeld, Hyojeong Lee, Hyunsuk Kim, Kyungmin Roh, Yunkyu Lee, Hyung Seon Song, Manoj Kumar, Samuel Yoffe, Dino A. Jaroszynski & Hyyong Suk
[Laser pulse compression by a density gradient plasma for exawatt to zettawatt lasers]Nature Photonics (2023)