Wu Sizhu, Wu Dong, Xu Jian, Hanada Yasutaka, Suganuma Ryo, Wang Haiyu, Makimura Testuya, Sugioka Koji, Midorikawa Katsumi
Laser Technology Laboratory, RIKEN – Advanced Science Institute, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
Opt Express. 2012 Dec 17;20(27):28893-905. doi: 10.1364/OE.20.028893.
We investigated the physical mechanism of high-efficiency glass microwelding by double-pulse ultrafast laser irradiation by measuring the dependences of the size of the heat-affected zone and the bonding strength on the delay time between the two pulses for delay time up to 80 ns. The size of the heat-affected zone increases rapidly when the delay time is increased from 0 to 12.5 ps. It then decreases dramatically when the delay time is further increased to 30 ps. It has a small peak around 100 ps. For delay time up to 40 ns, the size of the heat-affected zone exceeds that for a delay time of 0 ps, whereas for delay time over 60 ps, it becomes smaller than that for a delay time of 0 ps. The bonding strength exhibits the same tendency. The underlying physical mechanism is discussed in terms of initial electron excitation by the first pulse and subsequent excitation by the second pulse: specifically, the first pulse induces multiphoton ionization or tunneling ionization, while the second pulse induces electron heating or avalanche ionization or the second pulse is absorbed by the localized state. Transient absorption of glass induced by the ultrafast laser pulse was analyzed by an ultrafast pump-probe technique. We found that the optimum pulse energy ratio is unity. These results provide new insights into high-efficiency ultrafast laser microwelding of glass and suggest new possibilities for further development of other ultrafast laser processing techniques.
我们通过测量热影响区尺寸和结合强度对两个脉冲之间延迟时间的依赖性，研究了双脉冲超快激光辐照下高效玻璃微焊接的物理机制，延迟时间最长可达80纳秒。当延迟时间从0增加到12.5皮秒时，热影响区尺寸迅速增大。当延迟时间进一步增加到30皮秒时，它又急剧减小。在100皮秒左右有一个小峰值。对于最长40纳秒的延迟时间，热影响区尺寸超过延迟时间为0皮秒时的尺寸，而对于超过60皮秒的延迟时间，它变得比延迟时间为0皮秒时更小。结合强度表现出相同的趋势。从第一个脉冲引起的初始电子激发和随后第二个脉冲引起的激发的角度讨论了潜在的物理机制：具体来说，第一个脉冲诱导多光子电离或隧穿电离，而第二个脉冲诱导电子加热或雪崩电离，或者第二个脉冲被局域态吸收。通过超快泵浦-探测技术分析了超快激光脉冲引起的玻璃的瞬态吸收。我们发现最佳脉冲能量比为1。这些结果为玻璃的高效超快激光微焊接提供了新的见解，并为其他超快激光加工技术的进一步发展提出了新的可能性。
