超快雷射激發螺旋導線產生準相對論輻射

QUASI-RELATIVISTIC RADIATION FROM ULTRAFAST LASER EXCITED HELICAL WIRE

吳明雄(Ming-Hsiung Wu)

指導教授 ： 黃衍介

國立清華大學/電機資訊學院/光電工程研究所/碩士(2013年)

摘要

近幾年來許多的科學研究都與高功率超快雷射有關，因為相比於過去使用的雷射，它電磁場強度更強，更能去影響電子產生過去比較不容易看到的現象。本論文主要可以分成兩個部份，其一是建造一個高功率超快雷射放大器去驅動光陰極電子槍，進而產生電子束。其二是使用高功率的超快雷射去激發螺旋導線產生準相對論輻射。在第一部份，我們將利用啁啾脈衝放大器的架設方式來完成飛秒雷射的放大器。目前，我已使用脈衝延展器將種子光雷射展開到300飛秒，並且其能量約為1奈焦耳。下一步是將被展寬的脈衝送入再生放大器，使其得到106的增益。但由於脈衝挑選器的開關速度不夠快，所以先暫停，直到我們從國外訂購的高壓開關送到便會繼續架設。在第二部份，我們發現在自由電子雷射中聚頻磁鐵的輻射條件與雷射激發螺旋導線天線輻射很相似。我們做了些實驗包括量測電磁脈衝的速度與雷射激發螺旋導線纏繞於PVC塑膠管與沒纏繞PVC塑膠管的輻射。實驗結果顯示纏繞於PVC管的螺旋導線的速度比沒纏附PVC管的直導線還慢，且輻射頻率上有纏繞於PVC管的比沒纏繞於PVC管的低。我們很高興量測到的輻射頻率與相對論自由電子輻射的理論預測是非常接近的。在未來的工作部份，我們列舉了一些實驗方向，期許能透過那些實驗來對這些現象有更深的了解並加以運用。本論文主要的貢獻在於設計鈦藍寶石放大器以及發現超快雷射激發螺旋天線產生準相對論輻射。

關鍵字

雷射放大器 ； 相對論輻射輻射

並列摘要

High-power, ultrafast laser has been used in research because the strong electromagnetic field associated with an ultrafast laser can strongly interact with materials to generate a new phenomenon that differs from that under a weak electromagnetic field. This thesis is divided into two parts; the first part is related to the study of a Ti:sapphire laser amplifier and the second part is related to the use of a Ti:sapphire laser amplifier to excite an electric pulse in a helical wire to generate quasi-relativistic radiation.
For the first part, we attempted to build a femtosecond laser amplifier based on the chirped pulse amplification technique. The laser pulse width of the seed laser was first stretched to 300 ps from a Ti:sapphire oscillator. The energy of the stretched pulse was about 1 nJ. We used a Pockels Cell to select precisely the laser pulse from the oscillator for amplification. We expected that the amplification gain of the stretched pulse laser is on the order of 106 times in a regenerative amplifier. We completed the design of the regenerative amplifier and waited for a high-voltage switch to test the amplifier.
For the second part, we discovered that the radiation mechanism for a laser excited helical wire antenna is similar to that from a helical undulator. We carried out the measurements of radiation from ultrafast laser-excited helical wires in air and wrapped on a PVC tube. The measured radiation frequencies from both sets of data fit well to the theoretical model of undulator radiation. In the future, we will continue to investigate the physics of such radiation, including radiation power and stimulated emission.
The major contribution of this thesis includes the complete design of a Ti:sapphire amplifier and the demonstration of quasi-relativistic radiation from an ultrafast laser-excited helical wire.

並列關鍵字

laser amplifier ； quasi-relativistic radiation

參考文獻

[1] T. H. Maiman, “Stimulated Optical Radiation in Ruby”, Nature, 187, 493-494 (1960).

[2] Donna Strickland and Gerard Mourou, “COMPRESSION OF AMPLIFIED CHIRPED OPTICAL PULSES”, Opt. Comm., 56, 219–221 (1985).

[4] Mike Dunne, “A high-power laser fusion facility for Europe”, Nature Phys., 2, 2-5 (2006).

[5] J. Seres, V. S. Yakovlev, E. Seres, Ch. Streli, P. Wobrauschek, Ch. Spielmann and F. Krausz, “Coherent superposition of laser-driven soft-X-ray harmonics from successive sources”, Nature Phys., 3, 878 - 883 (2007).

[7] S. Fritzler, K. Ta Phuoc, V. Malka1, A. Rousse, and E. Lefebvre, “Ultrashort electron bunches generated with high-intensity lasers: Applications to injectors and x-ray sources”, Appl. Phys. Lett., 83, 3888-3890 (2003).