University of Seoul
광섬유 레이저와 산업 응용
이주한
Lasers & Optical Semiconductors Lab.
서울 시립대학교 전자전기컴퓨터 공학부
(e-mail : [email protected])
11
Outline
1. 동작 원리에 따른 레이저 구분 2. 레이저 종류
3. 레이저의 산업, 군사 응용
- Solid State Laser
- Semiconductor Laser
- Fiber Laser
동작 원리에 따른 Pulsed Lasers 의 종류
2
• Mode-locking
• Pulse width : Picoseconds ~ Femtoseconds
• Maximum Operating Frequency : 수십 MHz
• Passive or Active Schemes
• Applications : Fine Cutting, Sintering, Engraving, Welding
• Q-switching
• Pulse width : Microseconds ~ Nanoseconds
• Maximum Operating Frequency : 수백 kHz
• Passive or Active Schemes
• Applications : Materials Processing, Micromachining, Solar/ Photovoltaics, Scribing, Marking, Texturing, Ablation
• Quasi-CW
• Pulse width : Milliseconds
• Maximum Operating Frequency : 수십 Hz
• Active Schemes
• Spot Welding, Seam Welding, Microwelding, Drilling, Cutting, Medical Devices
Principle of Ultra-fast Mode-locked Pulse Lasers
3 Ultrafast laser Configuration
Ultrafast laser Configuration
Pump
HR
Gain
OC
Mode-locking
Mechanism
Dispersion
Compensation Cavity modes
Cavity modes
n= 2 L/n
Mode Locking
4
Out of phase
RANDOM phase for all the laser modes
Irradiance vs. Time
Time Time
The relative phases of the simultaneous lasing modes
must be locked at proper values
Mode Locking
5
Out of phase In phase Out of phase
LOCKED phases for all the laser modes
66
Mirror 1 Mirror 2
Q-switch Excited state
Excited state
Mirror 2 Mirror 1
Q-switch
Switch-off
Switch-on
Output Pulse
Operating Principle of Q-switching I
Ground state
Ground state Pump
Pump
Solid State Lasers
7 Laser Type Wavelength Pump Source Applications
Neodymium glass (Nd:Glass) laser
~1.062 μm (Silicate glasses), ~1.054 μm (Phosphate glasses)
Flashlamp, laser diode
Used in extremely high power (terawatt scale), high energy (megajoules) multiple beam systems for inertial confinement fusion. Nd:Glass lasers are usually frequency tripled to the third harmonic at 351 nm in laser fusion devices.
Titanium sapphire (Ti:sapphire) laser
650-1100 nm Other laser
Spectroscopy, LIDAR, research. This material is often used in highly-tunable mode-locked infraredlasers to produce
ultrashort pulses and in amplifier lasers to produce ultrashort and ultra-intense pulses.
Nd:YAG Laser
Semiconductor Lasers
8 Laser Type Wavelength Pump
Source
Applications
Semiconductor laser diode(general
information)
0.4-20 μm,
depending on active
region material. Electrical current
Telecommunications, holography, printing, weapons, machining, welding, pump
sources for other lasers.
GaN 0.4 μm Optical discs.
Fiber Lasers
9 Laser Type Wavelength Pump
Source
Applications
Yb-doped Fiber
Laser 1.03 ~ 1.06 μm, 975 nm, 915 nm LDs
weapons, machining, welding, Material Processing
Erbium-doped Fiber
Laser 1.53 ~ 1.6 μm 980 nm, 1480 nm
LDs
Telecommunications, Material Processing Thulium-doped Fiber
Laser 1.8 ~ 1.95 μm
790 nm Multimode LDs, 1560 nm Singlemode LDs
Plastic Processing, Medical Applications Holmium-doped Fiber
Laser 1.9 ~ 2.8 μm 1950 nm Fiber Laser,
1148 nm LDs Medical Applications
Fiber Lasers
• Advantages of Fiber lasers
• Lasers generating outputs at special wavelengths (visible ~ infrared spectral region)
• High power lasers with good beam quality
• High thermal dissipation due to distributed gain medium
• Compact Implementation
• High Environmental Stability due to no free space beam alignment required
• Technical Difficulties
• Polarization control
• Specialty fiber based device fabrication
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고출력 광섬유 레이저 기본 구조
•
단일 공진기 구조:•
공진기 자체에서 고출력 빔을 발생시키는 구조•
주공진기-파워증폭기 구조, Master Oscillator and Power Amplifier (MOPA):•
낮은 파워의 공진기 출력 빔을 고출력 증폭기로 증폭하는 구조11
고출력 이터븀 첨가 광섬유 단일공진기 구조 개략도
12 -
공진기 자체에서1kW 정도의 출력빔 발생
- Free-space alignment 필요
-
테스트용 레이저 구현 시 사용되는 구조주공진기 파워 증폭기 MOPA 구조 개략도
13
Master
Oscillator Isolator Optical
Fiber Laser Gain Medium
MOPA Output at 1.06 um Fiber-Coupled
Laser Diode Pump at 915 or 975nm
Fiber-Coupled Laser Diode Pump
at 915 or 975nm
Splicing point
Pump/Signal Combiner
-
상용 고출력 레이저에서 채택하는 구조로서 저출력의CW공진기 출력
을 증폭기로 증폭하는 구조
(Master Oscillator and Power Amplifier (MOPA)
-
전체 구조를 광섬유로 융착해서 구현할 수 있는 장점이 있음상용 광섬유 레이저
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DLR:1W-1kW YLM:<50W YLR-SM:<1kW YLR-LP:<500W
YLR-HP:<20kW
ELR:150W RLM:<30W TLR:<150W
YLP-HE:<10mJ YLP:<2mJ YLP-PS:<200nJ
ELP-775:<25W
Material Processing Using Pulse Lasers
https://www.youtube.com/watch?v=7k20Zp5aPjY
https://www.youtube.com/watch?v=Xe_jyx_crK
Y
• Airbone Laser Aircraft – Chemical Laser
• HEL-MD system – Fiber Laser
• US Navy Laser Killer Gun – Fiber Laser
Laser Weapons
https://www.youtube.com/watch?v=jIxugT-QiEI
의료용 레이저
17 Photon
Tissue Therapy
의술치료
Imaging
영상정보
• Two categories
•Therapy: High power laser beam to destroy/reshape tissue
•Imaging: Low power laser beam to collect back-scattered signal from tissue
https://www.youtube.com/watch?v=022pKzWiZX8