# Numerical Investigation of the Temporal Contrast in ps-OPCPA with Compact Double BBO Arrangement
## 4 Conclusions  
Motivated by the promising applications of intense few-cycle laser pulses with high temporal contrast, we are devoted to studying the ps-OPCPA schemes. Among the current systems, short-pulse OPCPA has particular advantages especially for the ultrabroad bandwidth and the high temporal contrast. However, it does pose great challenges for designing and constructing pump lasers with the duration of approximately 1 ps. The compact double BBO arrangement attracts us most because of its relative simplicity and potential high-performance output ability. In this paper, we present the five-wave-coupled equations to simulate the broadband amplification of signal and PSF. This numerical method is very convenient for investigating the amplification of PSF with different phase-matching conditions. It is found that the amplified energy of PSF with perfect phase-matching is little higher than the case of PSF having the same phase mismatch with the signal. In addition, much attention is paid to the calculation of the temporal contrast in the double BBO arrangement. According to our simulation, it can be concluded that the temporal contrast as high as \(2\times 10^{-11}\) and the ultrabroad spectrum ranging from 700 nm to 1200 nm can be simultaneously realized in the compact double BBO arrangement pumped by 100 ps  
Figure 6: (**a**) Temporal contrast in Config 1.1 (blue), Config 1.2 (orange), Config 2.1 (purple) and Config 2.2 (red). (**b**) Temporal contrast in traditional one BBO arrangement (pink) and Config 1.1 (blue).  
Figure 7: (**a**) A more realistic input spectrum (orange) and the amplified spectrum in the traditional single BBO configuration (pink) and in Config 1.1 (blue); (**b**) Temporal contrast in the traditional single BBO arrangement (pink) and Config 1.1 (blue) with a more realistic input spectrum.  
pulses. Numerical investigation in this work provides the theoretical guide for designing ps-OPCPA with the double BBO arrangement.  
Conceptualization, H.C. and Y.X.; Data curation, X.C., X.Y. ([PERSON]), F.W., X.Y. ([PERSON]), J.G., J.Q. and Y.X.; Funding acquisition, Y.X. and Y.L. ([PERSON]); Investigation, H.C. and Y.X.; Methodology, H.C., J.H., X.W., P.B., Z.Z. and Y.L. ([PERSON]); Project administration, Y.X. and Y.L. ([PERSON]); Software, H.C. and J.H.; Supervision, Y.L. ([PERSON]); Validation, Y.X. and Y.L. ([PERSON]); Visualization, H.C.; Writing--original draft, H.C.; Writing--review and editing, Y.X. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Key Research and Development Program of China (2017 YFE0123700); The Strategic Priority Research Program of the Chinese Academy of Sciences (XDB1603); National Natural Science Foundation of China (61925507); Program of Shanghai Academic Research Leader (18 XD1404200); Shanghai Municipal Science and Technology Major Project (2017 SHZDZX02); Shanghai Sailing Program (19 YF1453100); Natural Science Foundation of Shanghai (20 ZR1464600);Youth Innovation Promotion Association of the Chinese Academy of Sciences; International Partnership Program of Chinese Academy of Sciences (181231 KYSB20200040).  
**Infrared Consent Statement**: Not applicable.  
**Data Availability Statement**: All of the data reported in the paper are presented in the main text. Any other data will be provided on request.  
**Conflicts of Interest**: The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.