Laser-induced supersaturation and snow formation in a sub-saturated cloud chamber Jingjing Ju • Tomas Leisner • Haiyi Sun • Aravindan Sridharan • Tie-Jun Wang • Jingwei Wang • Cheng Wang • Jiansheng Liu • Ruxin Li • Zhizhan Xu • See Leang Chin Received: 27 April 2014 / Accepted: 26 August 2014 / Published online: 7 September 2014 Ó Springer-Verlag Berlin Heidelberg 2014 Abstract Calculation of the saturation ratio inside vortices formed below the ﬁlament in a sub-saturation zone in a cloud chamber was given. By mixing the air with a large temper- ature gradient, supersaturation was sustained inside the vor- tices. This led to precipitation and snow formation when strong ﬁlaments were created using short focal length lenses (f = 20 and 30 cm). However, when longer ﬁlaments were formed with the same laser pulse energy but longer focal length lenses (f = 50 and 80 cm), only condensation (mist) was observed. The lack of precipitation was attributed to the weaker air ﬂow, which was not strong enough to form strong vortices below the ﬁlament to sustain precipitation. 1 Introduction With the continuous improvement of laser technology, nonlinear effects in the process of laser–matter interactions become more and more signiﬁcant. Laser ﬁlamentation is one of many interesting outcomes of these nonlinear dynamics. It has been well studied and interpreted as a dynamic balancing process between the nonlinear Kerr self-focusing effect and the plasma-induced defocusing effect and so on [1–9]. In air, this balancing process clamps the intensity inside each ﬁlament to be about 5 9 10 13 W/ cm 2 , and plasma density of about 1 9 10 16 /cm 3 [1–9]. About 5 % of the laser energy is consumed during the laser ﬁlamentation [2, 10, 11] through multi-photon/tunneling ionization. This consumed energy is released into the sur- rounding environment as thermal energy, through plasma recombination and relaxation processes. Recently, it is found that the typical decay time of this thermal energy was of the order of a few milliseconds [12]. This indicates that by employing high repetition laser pulses (repetition rate C1 kHz), a steady thermal waveguide could form around the plasma column. The latter becomes a quasi- continuous heating source causing thermodynamic move- ment of air molecules in the medium. In air around saturation or supersaturation, laser ﬁlament has been proven to induce condensation through seeding the vapor with ions and hygroscopic molecules such as HNO 3 as cloud condensation nuclei (CCN) [13–20]. However, the inﬂuence of thermal heating by the laser ﬁlaments had not attracted any scientiﬁc attention in the laser-based rainmaking ﬁeld until 2012. By employing a 1 kHz 9 mJ/50 fs 800 nm Ti: sapphire laser system, we observed both laser-induced water condensation and snow formation inside a typical diffusion cloud chamber (around the ﬁlaments, the relative humidity was RH * 126 % and the temperature T * -28 °C) [21, 22]. This observation of localized precipitation (occupying an area of 2.0 9 1.5 cm 2 right below the ﬁlament center) was in fact out of everyone’s expectation, so called an ‘‘accident.’’ J. Ju (&)  A. Sridharan  T.-J. Wang  S. L. Chin Department of Physics, Engineering Physics and Optics and Center for Optics, Photonics and Laser (COPL), Laval University, Quebec City, QC G1V 0A6, Canada e-mail: jenny06@siom.ac.cn J. Ju  H. Sun  T.-J. Wang  J. Wang  C. Wang  J. Liu (&)  R. Li  Z. Xu State Key Lab of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Science, No. 390, Qinghe Road, Jiading District, Shanghai 201800, China e-mail: michaeljs_liu@mail.siom.ac.cn T. Leisner Institute for Meteorology and Climate Research, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany T. Leisner Institut fu ¨r Umweltphysik, Universita ¨t Heidelberg, 69120 Heidelberg, Germany 123 Appl. Phys. B (2014) 117:1001–1007 DOI 10.1007/s00340-014-5920-0