A cylindrical Öffner stretcher based on ternary reflector (COSTER) is proposed and analyzed. Compared with the traditional Öffner stretcher, the COSTER has no off-axis aberration in the multipass configuration, and the output laser of COSTER has lower spectral phase noise and higher temporal contrast in the far field. The COSTER is quite suitable to be used in multi-petawatt laser facilities, and it might be the preferred stretcher configuration for ultrafast and ultra-intense lasers.

High-performance 86 μJ, 11.2 fs pulses with a spectrum range of 800–1050 nm are generated based on 1030 nm, 190 fs Yb femtosecond pulses by using multi-plate-based spectral broadening and filtering. Taking advantage of single beam configuration, the obtained pulses have excellent power and spectral stabilities. Since the output spectrum is obtained by spectrally filtering the broadened components, the temporal contrast of the output pulses is enhanced by at least four orders of magnitude. Together with the robust and simple setup, the proposed method is expected to be a competitive option for the generation of seed pulses for 10s–100s petawatt lasers.

We demonstrate an ultra-broadband high temporal contrast infrared laser source based on cascaded optical parametric amplification, hollow-core fiber (HCF) and second harmonic generation processes. In this setup, the spectrum of an approximately 1.8 μm laser pulse has near 1 μm full bandwidth by employing an argon gas-filled HCF. Subsequently, after frequency doubling with cascaded crystals and dispersion compensation by a fused silica wedge pair, 9.6 fs (~3 cycles) and 150 μJ pulses centered at 910 nm with full bandwidth of over 300 nm can be generated. The energy stability of the output laser pulse is excellent with 0.8% (root mean square) over 20 min, and the temporal contrast is >10¹² at –10 ps before the main pulse. The excellent temporal and spatial characteristics and stability make this laser able to be used as a good seed source for ultra-intense and ultrafast laser systems.

Temporal contrast directly affects the interaction between ultraintense and ultrashort pulse lasers with matter. Seed laser sources with broad bandwidth and high temporal contrast are significant for overall temporal contrast enhancement. The technique of cascaded nonlinear processes with optical parametric amplification and second-harmonic generation is demonstrated for high temporal contrast seed source generation. Within 40 ps before the main pulse, the temporal contrast reaches over 10¹¹. The pulse energy and duration of the high-contrast pulse are 112 μJ and 70 fs, respectively. Considering its high beam quality and stability, this laser source can serve as a high-quality seed for Nd:glass-based ultraintense and ultrashort pulse laser facilities.

In this work, we propose and verify experimentally a model that describes the concomitant influence of the beam size and optical roughness on the temporal contrast of optical pulses passing through a pulse stretcher in chirped-pulse amplification laser systems. We develop an analytical model that is capable of predicting the rising edge caused by the reflection from an optical element in a pulse stretcher, based on the power spectral density of the surface and the spatial beam profile on the surface. In an experimental campaign, we characterize the temporal contrast of a laser pulse that passed through either a folded or an unfolded stretcher design and compare these results with the analytical model. By varying the beam size for both setups, we verify that optical elements in the near- and the far-field act opposed to each with respect to the temporal contrast and that the rising edge caused by a surface benefits from a larger spatial beam size on that surface.

为了提高再生放大器输出激光脉冲的对比度，需要同时提高激光脉冲纳秒尺度的对比度和皮秒尺度的对比度。利用普克尔盒对主脉冲和预脉冲时间滤波的方法，设计了普克尔盒的双通预脉冲清洁装置，通过该装置使再生放大器输出激光纳秒尺度的预脉冲对比度提高了5个数量级；利用频谱整形方法，通过在放大器腔内适当位置插入频谱整形滤波片使得主脉冲前400 ps处的放大自发辐射对比度提高了1个数量级。最终，在双通预脉冲清洁与腔内频谱滤波共同作用下，再生放大器输出激光纳秒尺度的预脉冲对比度从4.3×10^-4提高到了6.6×10^-10，放大自发辐射对比度（主脉冲前400 ps）从5.0×10^-8提高到了5.0×10^-9。

We demonstrate the simultaneous temporal contrast improvement and pulse compression of a Yb-doped femtosecond laser via nonlinear elliptical polarization rotation in a solid state multi-pass cell. The temporal contrast is improved to 10⁹, while the pulse is shortened from 181 to 36 fs, corresponding to a compression factor of 5. The output beam features excellent beam quality with M² values of 1.18 × 1.16. The total efficiency of the contrast enhancement system exceeds 50%. This technique will have wide applications in high temporal contrast ultra-intense femtosecond lasers.

The Orion laser facility at AWE provides multiple beams to target delivering synchronized pulses at both nanosecond and sub-picosecond duration. In the latter, the peak power approaches the petawatt level. This paper presents a conceptual design for potential development of these beamlines. This would deliver a significant enhancement of performance at the fundamental level. In addition, a new approach is described for the management of frequency conversion at high intensity, which may allow significantly enhanced performance at the second harmonic also.

Temporal contrast (TC) is one of the most important parameters of an ultrahigh intense laser pulse. The third-order autocorrelator or cross correlator has been widely used in the past decades to characterize the TC of an ultraintense laser pulse. A novel and simple single-shot fourth-order autocorrelator (FOAC) to characterize the TC with higher time resolution and better pulse contrast fidelity in comparison to third-order correlators is proposed. The single-shot fourth-order autocorrelation consists of a frequency-degenerate four-wave mixing process and a sum-frequency mixing process. The proof-of-principle experiments show that a dynamic range of ～10¹¹ compared with the noise level, a time resolution of ～160 fs, and a time window of 65 ps can successfully be obtained using the single-shot FOAC, which is to-date the highest dynamic range with simultaneously high time resolution for single-shot TC measurement. Furthermore, the TC of a laser pulse from a petawatt laser system is successfully measured in single shot with a dynamic range of about 2 × 10¹⁰ and simultaneously a time resolution of 160 fs.