从“强场原子物理”到“强场原子核物理”  

From“strong-field atomic physics”to“strong-field nuclear physics”

作　　者：王旭 Wang Xu(Graduate School,China Academy of Engineering Physics,Beijing 100193,China;Southern Center for Nuclear-Science Theory,Institute of Modern Physics,Chinese Academy of Sciences,Huizhou 516000,China)

机构地区：[1]中国工程物理研究院研究生院,北京100193 [2]中国科学院近代物理研究所南方核科学理论中心,惠州516000

出　　处：《物理学报》2024年第24期28-36,共9页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:12474484,U2330401,12088101)资助的课题.

摘　　要：20世纪80年代中期,啁啾脉冲放大技术(2018年诺贝尔物理学奖)突破了激光强度提升的瓶颈,激光强度跨越了原子单位的门槛(1个原子单位激光强度对应功率密度3.5×1016 W/cm2).这样强的激光场可以在原子、分子中诱导出高阶非线性响应,导致一系列新的物理现象,其中尤其重要的是高次谐波辐射和阿秒光脉冲产生(2023年诺贝尔物理学奖).随着强激光技术的进步,当前激光强度已达到1023 W/cm2量级,并在进一步提升中.这样强的激光场能否在原子核中诱导出类似的高阶非线性响应、将“强场原子物理”推进至“强场原子核物理”?最近的研究发现,当前的强激光至少可以在一个特殊的原子核,即钍-229原子核诱导出高阶非线性响应.这得益于该原子核存在一个能量极低的激发态和超精细混合效应对于光核耦合的增强.高阶非线性响应的触发可以极大地提升原子核的激发概率和调控效率.类似原子,被强激光驱动的原子核也会向外辐射高次谐波.“强场原子核物理”开始成为光与物质相互作用以及核物理研究的新前沿,提供基于强激光的原子核激发和调控新方案,以及基于原子核跃迁的相干光辐射新途径.In the mid-1980s,chirped pulse amplification(Nobel Prize in Physics 2018)broke through previous limits to laser intensity,allowing intensities to exceed the atomic unit threshold(1 atomic unit of laser intensity corresponds to a power density of 3.5×10^(16)W/cm^(2)).These strong laser fields can cause high-order nonlinear responses in atoms and molecules,resulting in a series of novel phenomena,among which high-order harmonic generation and attosecond pulse generation(Nobel Prize in Physics 2023)are particularly important.With the development of high-power laser technology,laser intensity has now reached the order of 10^(23)W/cm^(2)and is constantly increasing.Now,a fundamental question has been raised:can such a powerful laser field induce similar high-order nonlinear responses in atomic nuclei,potentially transitioning“strong-field atomic physics”into“strong-field nuclear physics”?To explore this,we investigate a dimensionless parameter that estimates the strength of light-matter interaction:η=DE_(0)/ΔE,where D is the transition moment(between two representative levels of the system),E_(0)is the laser field amplitude,DE_(0)quantifies the laser-matter interaction energy,andΔE is the transition energy.Ifη<<1,the interaction is within the linear,perturbative regime.However,whenη~1,highly nonlinear responses are anticipated.For laser-atom interactions,D~1 a.u.andΔE=1 a.u.,so if E_(0)~1 a.u.,thenη~1 and highly nonlinear responses are initiated,leading to the above-mentioned strong-field phenomena.In the case of light-nucleus interaction,it is typical thatη<<1.When considering nuclei instead of atoms,D becomes several(~5 to 7)orders of magnitude smaller,whileΔE becomes several(~5)orders of magnitude larger.Consequently,the laser field amplitude E_(0)will need to be 10 orders of magnitude higher,or the laser intensity needs to be 20 orders of magnitude higher(~10^(36)W/cm^(2)),which is beyond existing technological limit and even exceeds the Schwinger limit,where vacuum breakdown occurs.However,there

关 键 词：强场原子物理 激光核物理 高阶非线性响应 高次谐波 

分 类 号：O57[理学—粒子物理与原子核物理]