Independent and continuous third-order dispersion compensation using a pair of prisms Download: 736次
1. Introduction
The chirped pulse amplification (CPA) technique[1, 2] is commonly used to build high-power laser systems for various experiments and applications, such as laser-driven plasma accelerators and fast ignition in inertial confinement fusion. Peak laser powers of up to 1 PW are now achievable, and are expected to be boosted to the EW level in the near future[3].
In CPA ultrashort laser systems, the dispersion elements include stretcher, compressor and amplifier material[4–10]. The compressor can completely compensate for group delay dispersion (GDD) and partly compensate for third-order dispersion (TOD), which are generated by the stretcher and amplifier material[6, 7]. However, compensating for the residual high-order dispersion is extremely important in the entire system to obtain the shortest pulse duration and highest pulse contrast, particularly for ultrashort pulses ()[3, 5]. Thus, setting up an independent dispersion compensation element is necessary to compensate for the residual high-order dispersion of the system.
Fig. 1. Ray-tracing sketch for a pair of identical isosceles prisms in a parallel face configuration.
The prism pair is an important element in dispersion compensation. In 1984, Fork
In this study, we focus on independent and continuous TOD compensation using a pair of prisms. The dispersion of the pair of prisms is analyzed in detail using a ray-tracing method operating at other than tip-to-tip propagation of the prisms. The variations of GDD and TOD for the pair of prisms are calculated with respect to the incident position and the separation between the prisms. A pair of prisms can provide a wide range of independent and continuous TOD compensation. The effect of residual TOD (RTOD) on the pulse contrast ratio and pulse duration is calculated. The RTOD not only worsens the pulse contrast ratio, but also greatly increases the pulse duration to the hundreds of femtosecond range for a tens of femtosecond pulse, even when small RTOD is employed. These phenomena are helpful in compensating for residual high-order dispersion and in understanding its effect on the pulse contrast ratio in ultrashort laser systems.
2. Model
Figure
Based on Figure
Fig. 2. At the central wavelength, GDD and TOD change with . Material: ; simulation parameters: , , , , , and .
To ensure high transmission efficiency of the prism pairs, Brewster angle incidence is adopted. The values of these angles can be calculated using , , , , where is the central wavelength.
The total phase for the pair of prisms yields
According to Equation (
3. Numerical results
According to the model constructed in Section
During the simulation, we adopted a typical Sellmeier series equation to describe glass material dispersion[2]. The Sellmeier series equation is written as
Table 1. Sellmeier coefficients for Equation (7 ) obtained from the Thorlab catalog[17].
|
3.1. Influence of distances and on dispersion
At the central wavelength, GDD and TOD change with distance or (Figures
Figures
In the simulation shown in Figure
In the simulation shown in Figure
Fig. 3. At the central wavelength, GDD and TOD change with . Material: ; simulation parameters: , , , , , and .
Fig. 4. At the central wavelength, GDD and TOD change with . Material: ; simulation parameters: , , , , , and .
3.2. Influence of distance on dispersion
At the central wavelength, GDD and TOD change with (Figure
During the simulation, the following parameters are employed: , , , , , and ; material: .
Fig. 5. At the central wavelength, TOD changes with and when . Simulation parameters: , , , , and ; material: .
Fig. 6. At the central wavelength, TOD changes with and when . Simulation parameters: , , , , and ; material: SF10.
3.3. TOD independent and continuous compensation
Based on the analyses in Sections
In the simulation shown in Figure
Fig. 8. Effect of RTOD on pulse duration. The figure on the right is a magnified section of the figure on the left.
3.4. Effect of RTOD on pulse contrast ratio and pulse duration
To demonstrate the effect of RTOD on the pulse contrast in CPA lasers, we employed a 30 fs compressed pulse laser system as a example. The central wavelength is and the spectral width is 140 nm. The spectral functions of the pulse exiting the compressor are assumed to have a Gaussian shape. The final output pulse contrast is calculated using a model in Ref. [2].
Figure
4. Conclusion
In summary, a ray-tracing model is presented to calculate the dispersion of a pair of prisms operating at other than tip-to-tip propagation of the prisms. The pair of prisms can provide a wide range of independent and continuous TOD compensation by employing appropriate values of and or and simultaneously, which is helpful in compensating the residual high-order dispersion of the CPA laser system. RTOD not only worsens the pulse contrast ratio, but also increases the pulse duration to the hundreds of femtosecond range for a tens of femtosecond pulse, even at small RTOD. These phenomena are helpful in understanding the effect of residual high-order dispersion on the pulse contrast ratio in ultrashort pulse laser systems.
[1]
[2]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
[11]
[12]
[13]
[14]
[15]
[16]
Article Outline
Qingwei Yang, Xinglong Xie, Jun Kang, Haidong Zhu, Ailin Guo, Qi Gao. Independent and continuous third-order dispersion compensation using a pair of prisms[J]. High Power Laser Science and Engineering, 2014, 2(4): 04000e38.