슬라이드 1

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1 레이저의원리와응용 이병호서울대전기공학부

2 Einstein Imagination is more important than knowledge. For knowledge is limited to all we now know and understand, while imagination embraces the entire world, and all there ever will be to know and understand. Albert Einstein ( )

3 흡수와자발방출 흡수 (Absorption) 자발방출 (Spontaneous Emission)

4 유도방출 (Stimulated Emission)

5 Einstein s A,B Coefficients ω = E2 E 1 A 21 N + N2 1 = (spontaneous B12 u ( f, T ) ( absorptopn rate) N emission rate) B21 u ( f, T ) ( stimulated emission rate)

6 Einstein s A,B Coefficients dn dt = dn dt = N A N B u( f, T ) + N B u( f, T ) ( ω) u( f, T) = WT = A N N B B ( ) ( E kbt) ( ) N g 1 1exp 1 g 1 hf = = exp N2 g2exp E2 kbt g2 kbt u( f, T) = A21 g g hf kt B B ( ) exp( ) 1 2 B 12 21

7 Einstein s A,B Coefficients g = 1B12 g2b21 ( ω π c ) B21 = A21

8 Laser 의특성 단색성 고휘도 지향성 가간섭성 (Coherency)

9 LASER Light Amplification by Stimulated Emission of Radiation 이득매질 거울 거울 양자역학적인광자와물질사이의상호작용을이용한광원

10 LASER 의개략도

11 Coherency An ideal monochromatic source of light has a group of photons with exactly one frequency. An ideal coherent source of light has a group of photons with the same relative phase. Real laser sources are neither perfectly monochromatic nor perfectly coherent. A real laser will have a finite linewidth and finite coherency.

12 Laser 의역사 1917 Einstein Stimulated Emission 1940s Fabrikant 박사학위논문 1950s Townes, Weber, Prokhorov, Basov -MASER 1954 Gordon, Townes, Zeiger 최초의 maser 1957 Gould LASER 특허출원 1958 Schawlow, Townes Intrared and Optical Masers 논문 Maiman 최초의레이저동작 (Ruby laser) Javan, Bennett, Herriott 최초의 cw 레이저동작 (He-Ne laser) laser flood

13 Laser 가늦게발명된이유 Charles H. Townes (1915-) 대부분의물리학자들은전자공학과증폭기에대해서몰랐었고, 전기공학자들은대개양자역학을배우지않았다. 하지만제 2 차세계대전으로인해레이다 (radar) 개발을위해공학자들과자연과학자들이함께일하게되었고, 물리학자들이전자공학에접근할수있게되었다.

14 최초의레이저 루비레이저 Theodore Harold Maiman ( ) 최초의레이저 : 1960 년, Maiman 이만든세계최초의레이저, 루비를레이저매질로사용

15 Laser Oscillation (I) A laser can only lase at those wavelengths (longitudinal modes) for which an integral multiple of half-wavelengths fit into the cavity.

16 Laser Oscillation (II)

17 발진회로와의비교 Gain = 이득매질 Feedback& 주파수선택 = 공진기 ( 거울 )

18 3- 준위및 4- 준위레이저 A three-state laser consists of a ground state(0), an upper laser state(2), and a pumping state or states(3). A four-state laser consists of a ground state 0, a pumping state(or band of states) 3, an upper laser state 2, and a lower laser state 1.

19 Linewidth Broadening Homogeneous broadening - Lifetime broadening - Collision broadening Inhomogeneous broadening - Doppler broadening

20 Lifetime Broadening E 2 Δν = 1 1 2π τ1 1 + τ 2 E 1 g ( ν ) = Δν 2π ( ν ν ) 2 + ( Δν ) Lorentzian lineshape function

21 레이저의종류 매질의종류에따라고체 : 루비레이저, Nd:YAG 레이저, Ti:Sapphire 레이저, 광섬유레이저, 기체 : 탄산가스레이저, 헬륨 - 네온레이저, 아르곤이온레이저, 엑시머레이저, 기타 : 색소레이저, 자유전자레이저 발진종류에따라연속파 (cw: continuous wave) 레이저펄스레이저 : ~ 아토초까지가능 파장에따라가시광선, 적외선, 자외선, ~X-ray

He-Ne Laser 1961 년 Javan, Bennett, Herriott 세사람은헬륨 (He) 과네온 (Ne) 의혼합기체를이용하여최초로 1152.3nm 의적외선의연속발진에성공 오늘날에는이레이저는수밀리와트의가시광선 (632.

22 He-Ne Laser 1961 년 Javan, Bennett, Herriott 세사람은헬륨 (He) 과네온 (Ne) 의혼합기체를이용하여최초로 nm 의적외선의연속발진에성공 오늘날에는이레이저는수밀리와트의가시광선 (632.8nm) 을발진하게하여실험실에서간섭을이용한측정, 홀로그래피의제작등에널리쓰고있다. 0.8 torr 의 He 과 0.1 torr 의 Ne 의혼합기체를가늘고긴관속에넣어두고방전시킨다. 헬륨은네온을들뜨게하는매개물질로서작용하여실제의발진은네온에서이루어진다.

23 Argon Ion Laser 의특징 Ar-Ion 레이저는가스레이저로서 He-Ne 레이저와유사 Ar-Ion 레이저는전리 (ionization) 와여기 (excitation) 을위하여대단히높은전류가인가되어야한다. Blue-green 범위에서 100W 이상을공급할수있다. 이온레이저는고전류방전으로여기되는데높은전류밀도는기체를이온화시키고이온들을고준위로여기시킨다. 상위레이저준위가 36 ev 로매우높다. 강력한여기가필요하다.

24 Nd:YAG Laser 의특징 YAG(yttrium aluminum garnet) 결정안의 Nd 가레이저물질 Nd:YAG 레이저는 100W 이하의연속파혹은수 MW 의짧은펄스를만들어내므로응용범위가상당히넓다. 외부광원에의해여기 레이저용접, 의료용, 핵융합

25 CO 2 Laser Carbon dioxide laser cutting system. Normal modes of the carbon dioxide molecule.

26 Excimer Laser 의내외부

27 Dye Laser 색소레이저는유기색소분자를알코올등에용해시켜레이저매질로사용 액체레이저 색소의종류나농도를변화시켜, 0.3 μm 1.2 μm범위의근자외선, 가시광, 근적외선의넓은범위에걸쳐연속파장가변이되는레이저가가능하다. 광여기방법 극초단펄스, 의료용

28 반도체레이저 (DFB LD) 구조도

29 광섬유레이저의예

30 Schematic of the fiber laser Dichroic mirror 915 nm ~1um Lens Lens Beam block Water Cooling system Current Driver Mirror Diode Lens Dichroic mirror 915 nm ~1um Dichroic mirror 915 nm Yb-doped double-clad ~1um optical fiber Beam block Remaining pumping bema Signal End-pumping scheme Two dichroics protect the pump source by blocking signal. Gain medium: Yb-doped double-clad fiber (DCF) Laser cavity is composed of the flat-cleaved facet and the bulk feedback (signal) mirror.

31 Fiber laser characteristics Yb-doped double-clad fiber Core diameter: 9 μm NA: 0.11 Inner-cladding diameter: 150 μm Low index coating: outer cladding Cladding pump absorption: 0.8 db/m Fiber length: 10 m

32 Yoonchan Jeong 내가말하는것이항상옳은것은아닐지라도, 내가옳다고여기는것이라야세상에떳떳이말할수있다고하신단재선생님의말씀을마음속에새겨언제나부끄럽지않은연구를하고싶다. ( 과학동아 2004 년 8 월 )

33 간섭계를이용한진동해석 fixed mirror Michelson 간섭계 sample laser λ/4 λ I( f ) max + + min λ/2

34 ESPI Laser Reference beam Electronic Speckle Pattern Interferometry Illumination direction Measuring direction Measuring object Camera, CCD Observation direction

35 진동모드측정의예

36 Interferometry

37 Double-Exposure Holographic Interferometry (a) (b)

38 Holography Dennis Gabor (1948, 1949, 1951) Nobel Prize in Physics (1971) holography whole recording - On-axis hologram E. N. Leith and J. Upatnieks (1962, 1963) - Off-axis hologram Y. N. Denisyuk (1962, 1963, 1965)

39 Founders of Holography Yuri Denisyuk ( ) Dennis Gabor ( ) Emmett Leith ( ) Stephen A. Benton ( )

40 Gabor Hologram ( x, y) = A a( x, y) 2 I + 2 ( x, y) + A a( x, y) + Aa ( x y) 2 = A + a,

41 Leith-Upatnieks Hologram ( x, y) = Aexp( j2παy) + a( x y) U, α = I sin 2θ λ 2 2 ( x, y) = A + a( x, y) + A a( x, y) exp( j2παy) + Aa ( x, y) exp( j2παy)

42 Requirement of of Reference Beam Angle (a) (b) ( 3 ) 1 2θ = sin Bλ min

43 Hologram Examples Bird and Train, by Emmett N. Leith and Juris Upatnieks, 1960, one of the earliest laser transmission images. The Seed, an abstract white light transmission hologram by Dan Schweitzer, 1980.

44 Optical Storage Roadmap

45 History of Optical Memory Technology * 2005 Topical Meeting on Nano-Optical Probe

46 DVD (digital versatile disc) 구조 외형은 CD 와동일 직경 120mm, 두께 1.2mm 의얇은알루미늄 원판에플라스틱막이보호막으로덮여있음. 내부구조 옆면을자세히보면 2 장의디스크가겹쳐있음. 용량늘리기 를위해 0.6mm 원판 2 장사용 DVD Construction DVD Disc Layout and Dimension * 출처 : Deluxe Global Media Services Ltd.

47 Blu-ray (blue-violet laser to to read and write data) What is blu-ray? Blu-ray, or Blu-ray Disc (BD) is the name of a next-generation optical disc format jointly developed by the Blu-ray Disc Association (BDA). The format was developed to enable recording, rewriting and playback of high-definition video (HD), as well as storing large amounts of data. A single-layer Blu-ray Disc can hold 25GB, which can be used to record over 2 hours of HDTV or more than 13 hours of standard-definition TV. There are also dual-layer versions of the discs that can hold 50GB. Blu-ray is expected to replace VCRs and DVD recorders over the coming years, with the transition to HDTV.

48 Blu-ray 제조업체 Blu-ray recorders Hitachi JVC LG Mitsubishi Panasonic Philips Pioneer Samsung Sharp Sony Zenith SAMSUNG Blu-ray media Fujifilm JVC Maxell Mitsubishi Panasonic Samsung Sony TDK SAMSUNG Sony Fujifilm Sony

49 광섬유 (Optical Fiber) 센서와신호전달의역할을동시수행 분배형센서의실현이용이 원격측정가능 (~0.2 db/km loss) 기존센서기술로불가능한부분을커버

50 통신의역사 1830 년대 --- Morse : 전신기술의발명 ( 전송속도 : < 10b/s ) 대서양횡단전신케이블 Bell : 전화의발명 1940 년경 --- 3MHz 동축케이블전송기술 1950 년대 --- Microwave 무선전송기술 ( 전송속도 : < 100Mb/s )

51 광통신의역사 I 1950 년대 --- Townes, Schawlow, Basov, Prokhorov : Laser 의원리 최초의 laser 개발 광섬유통신의가능성발표 저손실광섬유의가능성 ( 20dB/km ) 상온에서의 cw 반도체레이저 세대광전송시스템 : 0.8µm GaAs 레이저, 다중모드광섬유 ( BL ~ 500Mb/s km )

52 광통신의역사 II II 1976~ 최초의현장적용시험및상업화시도 세대광전송시대의개막 : 1.3µm InGaAsP 레이저 dB/km 광섬유개발 µm InGaAsP 레이저개발 최초의대서양횡단광케이블 1.55µm 양자우물레이저개발 3 세대광전송의연구 ( 1.55µm,~10Gb/s ) 현재 세대 : 파장분할다중화 (WDM) 방식, 광증폭기, Soliton 연구 (5 세대 )

53 광통신의장점 전송용량의증대 고신뢰성 무중계거리의확대 보안성의증대 크기및무게의감소 무한한성장가능성 저가의시스템

54 통신의발전추세

55 광섬유의종류 다중모드광섬유 (MMF) 코어직경은 50μm 모드간분산에의해전송거리제한 단일모드광섬유 (SMF) 코어직경은 8μm 색분산에의해전송거리제한

56 단일모드광섬유의종류

57 WDM 전송에요구되는기술들 Source types Laser λ control Laser aging Standard λ Channel spacing... Gain flattening Dynamic gain control Gain bandwidth... Dispersion compensation Nonlinearities... Demultiplexer Demux λ control Bandwidth Crosstalk... Operation, Administration, Maintenance Issues...

58 개략적인계위별망구조 광섬유망 광섬유망 광섬유선로구간 평행 / 동축선로구간 교환국 ONU FTTO 교환국 RN 교환국 교환국 교환국 교환국 RN RN ONU ONU ONU ONU FTTC FTTH ONU ONU 기간망 메트로망 가입자망

59 우리나라의기간망

60 해저광케이블 I

61 해저광케이블 II

62 Nonlinear Optics Nicolaas Bloembergen (1920-) The future always belongs to the younger generation. Since the field continues to attract bright students, it may be expected that unexpected new developments will occur. Generally, history is highly nonlinear, and the course of revolutions and the rise and fall of empires is difficult to predict. The future course of nonlinear optics is also unpredictable.

레이저의 종류

레이저의 종류 레이저의종류 이병호서울대전기공학부 byoungho@snu.ac.kr 레이저의종류 매질의종류에따라고체 : 루비레이저, Nd:YAG 레이저, Ti:Sapphire 레이저, 광섬유레이저, 기체 : 탄산가스레이저, 헬륨 - 네온레이저, 아르곤이온레이저, 엑시머레이저, 기타 : 색소레이저, 자유전자레이저 발진종류에따라연속파 (cw: continuous wave) 레이저펄스레이저