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第五章 Laser 材料

第五章 Laser 材料. 授課大綱. 雷射的定義、形成 雷射原理 雷射組成 雷射種類. Laser 定義. LASER 是 『 L ight A mplification by S timulated E mission of R adiation』 Taiwan  雷射 ( 取其音 ) China  激光 ( 取其意 ). 3. 雷射的發展. 19 世紀中葉：電磁理論 20 世紀初期：量子論 1916 年：「受激輻射」概念 1954 年：受激輻射微波放大器 1960 年：紅寶石雷射. 雷射的發現.

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第五章 Laser 材料

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  1. 第五章 Laser 材料

  2. 授課大綱 • 雷射的定義、形成 • 雷射原理 • 雷射組成 • 雷射種類

  3. Laser 定義 • LASER 是『Light Amplification • by Stimulated Emission of • Radiation』 • Taiwan  雷射(取其音) • China  激光(取其意) 3

  4. 雷射的發展 • 19世紀中葉：電磁理論 • 20世紀初期：量子論 • 1916年：「受激輻射」概念 • 1954年：受激輻射微波放大器 • 1960年：紅寶石雷射

  5. 雷射的發現 1960年，梅曼(Maiman) 以人造紅寶石發出了有序的雷射光。較之傳統光源所發出來的光，雷射光至少有以下四大特性： 1.方向性(directionality) 2.純色性(monochromaticity) 3.同調性(coherence) 光同調性的外在表現有二，分別是： (1)純色性 (2)干涉性 4.高強度 5

  6. 原子能階 E3 E2 基態 E1

  7. 雷射原理

  8. 雷射原理 • 一、原子能階： • 波爾原子傳說： • 電子只在特定能階存在（非連續） • 在熱平衡狀態下大部分處於基態） • 粒子以波茲曼函數分佈：

  9. 雷射原理 E2 p12 Optical absorption E1 (1)吸收作用： 由低能階→高能階 需要供給熱、電、光、化學作用、… 吸收機率：Pa N2=Pa•N1

  10. 雷射原理 E2 Spontaneous emission E1 (2)自發放射： 由高能階→低能階 放出光、熱、…………轉移（雜亂無章） 自發機率：Psp N1=Psp•N2

  11. 雷射原理 (3)受激放射： 由高能階→低能階（伴隨放出） 同方向、同頻率、同相位、 …………（共鳴） 受激機率：Pst N1=Pst•N2 由愛因斯坦理論知 Pst=Pa

  12. 雷射原理 二、居量反轉（Population Inversion） 熱平衡狀態：E2>E1時，N2<N1 則pst•N2<Pa•N1 →產生吸收作用 倒轉分佈時：E2>E1時，N2>N1 則pst•N2>Pa•N1 →產生放大作用

  13. 雷射原理 三階雷射 四階雷射

  14. 雷射原理

  15. 雷射組成

  16. 雷射結構

  17. 激勵系統

  18. 活性介質

  19. 雷射種類

  20. 雷射分類

  21. 各種雷射的波長

  22. 氣體雷射系統

  23. He-Ne 雷射 􀂄 The first CW laser, as well as the first gas laser, was onein which a transition between the 2S and the 2P levels in atomic Ne resulted in the emission of 1.15 μm radiation. 􀂄 Transitions in Ne were used subsequently to obtain laser oscillation at λ0 = 632.8 nm and at λ0 = 3.39 μm. 􀂄 The operation of this laser can be explained as follows: a dc (or rf) discharge is established in the gas mixture containing, typically, 1.0 mm Hg of He and 0.1 mm Hg of Ne. The energetic electrons in the discharge excite helium atoms into a variety of excited states. In the normal cascade of these excited atoms down to the ground state, many collect in metastable levels 23S and 21S. Since the metastable levels nearly coincide in energy with the 2S and 3S levels of Ne, they can excite Ne atoms into these two excited states

  24. 固體雷射：紅寶石

  25. 固體雷射：Ti:Sapphire 􀂄 Since laser action was first reported by P. F. Moulton in 1982, the Ti:sapphire (Ti:Al2O3) laser, which has a broad tuning range of about 400 nm, has been the most widely used tunable solid-state laser. 􀂄 Crystal of Ti:sapphire exhibits a broad absorption band, located in the bluegreen region of the visible spectrum with a peak around 490 nm. The Ti:sapphire laser is, with a peak of the gain curve around 800 nm. 􀂄 Commercial Ti:sapphire lasers are usually pumped by argon lasers to obtaincw (continuous wave) output, and by frequency-doubled Nd:YAG, Nd:YLF, or Nd:YVO4 lasers for pulsed operation. 􀂄 Tuning ranges from about 700 nm to 1050 nm require several (usually three) sets of cavity mirrors. For pulsed solid-state lasers as pump source, output energies range from a few mJ at repetition rates of around 1 kHz, to 100 mJ per pulse at 20 pps. 􀂄 A very important application of Ti:sapphire lasers is the generation and amplification of femtosecond (10-15 sec) mode-locked pulses. A pulse width of a few tens of femtoseconds may be obtained easily from the Ti:sapphire lasers.

  26. 半導體雷射 􀂄 The material is “semiconductor” - At very low temperature, their conductivity is low - At high temperature, they act like conductors (temperature ↑ ⇒ conductivity ↑) (For metals: temperature ↑ ⇒ conductivity ↓) 􀂄 They are (the most widely used) “lasers” - Active medium ⇒ p-n junction (active layer) - Pumping scheme ⇒ Current injection (usually) - Laser mirrors ⇒ Cleaved end surfaces (usually)

  27. 光電半導體材料

  28. 半導體雷射:GaAs • p型GaAs與n型GaAs相接觸，而造成一介面成活化(active) 或空乏(depleted) 區，此為半導體工程中所習知者：在此區中既無電子亦無電洞(hole)，這是因為電子與電洞合併而消失，而稱之為「空乏區」。 圖4.9　正負砷化鎵接面空乏區示意圖，在施以正向偏壓時將電子及電洞驅入空乏區，電子及電洞復合而造成電流。

  29. 半導體雷射:異質結構 AlGaAs/GaAs

  30. 半導體雷射:異質結構 AlGaAs/GaAs

  31. 半導體雷射:異質結構 AlGaAs/GaAs(埋入式)

  32. 豎直空腔面發射雷射 (VCSELs)

  33. 豎直空腔面發射雷射 (VCSELs)

  34. 豎直空腔面發射雷射 (VCSELs)

  35. 準分子雷射 所謂準分子，是指ArF*,KrF*,XeCl*等分子。如「 ArF*」上標「*」符號，表示分子是在受激態。 準分子及其雷射波長分列於下：

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