# Single-Shot Temporal Contrast Enhancement Measurement of a Plasma Mirror by a Chirped Pulse
## 1 Introduction  
In the past three decades, high-power ultrashort pulse lasers have been significantly improved with the rapid development of femtosecond technology and chirped pulse amplification (CPA) [1]. Several petawatt ultrashort pulses are currently available at petawatt-class laser facilities [2], such as APOLLON [3] and the extreme light infrastructure (ELI) facilities [4], etc. The duration of the ultrashort pulse reaches tens of femtoseconds,and the focused light intensity is up to 10\({}^{21}\) W/cm\({}^{2}\)[3], providing extreme physical conditions for various high-energy physics, including fast ignition of the compressed inertial fusion targets, laser-driven particle acceleration, and diagnostics for high-energy-density physics [5; 6; 7; 8]. In addition to the power density, the physical results of the laser-plasma interaction are strongly dependent on the temporal profile of the high-power laser pulse. Nevertheless, the undesired temporal noises are always in existence accompanied by the amplified spontaneous emission, parametric fluorescence, and temporal phase modulation during the process of CPA or optical parametric chirped pulse amplification (OPCPA) [9]. These temporal noises appear as the pulse pedestals, coherent wings, and leading edge of the main pulse [10], and even strong pre-pulses, interacting with the target prior to the main pulse and eventually resulting in unsatisfactory experimental results. To suppress the temporal noises of the pulses, various of pulse-cleaning techniques have been reported, including saturable absorber (SA) [11], cross-polarized wave generation (XPW) [12], Fourier-filtering [13], picosecond optical parametric amplification (ps-OPA) [14] applied before compression, frequency doubling by second harmonic generation (SHG) [15], and plasma mirrors (PMs) [16; 17; 18] applied after compression. Among these methods, PMs exhibit an excellent pulse-cleaning performance for high-power ultrashort pulses. It can effectively and directly suppress all pulse noise after compressing under ultra-high laser intensity. The temporal contrast enhancement is the ratio between the reflectivity of the PM and cold reflectivity, and usually 2-3 orders of magnitude. To evaluate the performance of PMs, the measurement of the reflectivity, beam quality, and temporal contrast enhancement are typically necessary. The reflectivity and beam quality can be easily obtained by calorimeters and cameras. However, the temporal contrast enhancement measurement is complicated and challenging, especially in an online, high-energy physics experiment, owing to the characteristics of single-shot usage. In most PM experiments, the methods of the temporal contrast measurement are based on the delay-scan third-order cross-correlator [19; 20; 21; 22; 23], such as Sequoia, which is used for precise temporal contrast measurement with a dynamic range of \(\sim\)10\({}^{10}\) and a resolution of \(\sim\)one-hundred-femtoseconds. However, delay-scan methods require a lot of shots with the given repetition rate and cannot be used in a single-shot experiment. Meanwhile, the multiple shots undoubtedly increase the complexity and instability of the measurement. For most single-shot measurement methods, the low dynamic range (\(<\)10\({}^{6}\)) is far from meeting the application requirements (\(>\)10\({}^{9}\)) for high-power ultrashort pulses. One typical research reported by [PERSON] et al. was that they successfully measured a temporal contrast of \(>\)10\({}^{10}\) for a single-shot pulse in 2014 [24], which achieves an improvement by several orders of magnitude. However, the method is also complicated with a relatively high cost. The enhancement measurement requirement of 10\({}^{2}\)-10\({}^{3}\) of a PM is not worthwhile making big cost to achieve the single-shot temporal contrast measurement of 10\({}^{12}\) or even better. Thus, it is important to develop a convenient single-shot temporal contrast enhancement measurement of PMs.