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Lecture 10
Chapter VI Some Specific Laser Systems
Highlights
1. Solid State Lasers
3. Organic-Dye Lasers
2. Gas Lasers
Ruby Laser
Ti:Sapphire laser
He-Ne Laser
Carbon Dioxide (CO2) Laser
Ar+ Laser
4. Novel Lasers
Excimer Laser
Free Electron Laser
Chemical Laser
Nd3+: YAG Laser
Nd:Glass Laser
§6.0 Basic Structure of a Laser System
I. Basic Compose of a Laser System
Gain Media
Pumping Source
Total ReflectiveMirror
Partial ReflectiveMirror
LaserOutput
A) Gain Media: population inversion
B) Pumping Source:
Optical Pump
Electric DischargeChemical Reaction Pump
Nuclear Energy Pump: high energy particles
C) Optical Resonator: accumulate stimulate radiation
§6.0 Basic Structure of a Laser System
II. Types of Laser Systems
According to the gain media
Solid State Laser
Gas Laser
Dye Laser
Free Electron Laser
Semiconductor Laser
Optical Fiber Laser
According to the operation methods
Continuous Wave (CW) Laser
Pulse Laser
Q-Switch Laser
Mode-Lock Laser
According to the wavelength
Infrared Laser
Visible Laser
UV Laser
X ray Laser . . . . . .
§6.0 Basic Structure of a Laser System
III. The Properties of Laser
方向性: 由发散角来度量,几个 mrad, 接近衍射极限Dm
22.1
单色性: 由辐射激光脉宽决定, )(
相干性: 相干意味着波和波之间有确定的位相关系
时间相干性:同一空间点在不同时刻波场之间的相干性
c
ctL cc
由相干长度来度量,即在光传播方向上两个不同点处的光波场具有相干性的最大空间间隔。
空间相干性:不同空间点在同一时刻波场之间的相干性
)(
S由相干面积来度量。
高亮度:
S
PB
§6.1 Solid State Lasers
Generally speak, solid state lasers usually pumped by optical methods: such as flash lamp and diode laser
Flash lamp Pump
Laser Diode Pump (DPSSL – Diode Pumped Solid-State Laser)
1. Direct Head Face Pump
2. Fiber Coupling Head Face Pump
3. Side Face Pump
Laser diode array
Reflective plane
%31
%2510
VCSEL
I. Ruby Laser
§6.1 Solid State Lasers
--- the world first laser
32OAl doped with 32OCr
蓝宝石
淡红色
红宝石
2R (47%) 692.9nm
However, due to the very fast
relaxation process of and ,
after R1 oscillation R2 will be
ceased.
E A2
%)53(R1694.3nm
Three level system
Output Properties:
High pump rate threshold, usually operate in pulse type, multimode oscillation, coherence not good, need FP etalon for longitudinal mode and iris for transverse mode selection
Hz103~ 11 W10~ 9 10ps~
Blue light band
Green light band
A2
E
14 F
24 F
E2 -1cm29
24 A
1R2R
3Cr
§6.1 Solid State Lasers
II. Nd3+: YAG Laser
§6.1 Solid State Lasers
12533 OAlY:Nd 掺钕钇铝石榴石
(淡紫色)
Four level system
11/24
3/24 IF μm06.1
9/24
3/24 IF 50nm9
13/24
3/24 IF μm32.1
F4
μm32.1
3Nd
μm06.1nm950
3/24 F
9/24 I
11/24 I
13/24 I
strongest
Fluorescence Power
medium
weakest
Three level system, threshold very high
Depressed due to 1.06um oscillation
1000W~CW: MW hundred several~Pulse:
§6.1 Solid State Lasers
Material processing, rangefinding, laser target designation, surgery, research, pumping other lasers (combined with frequency doubling to produce a green 532 nm beam). One of the most common high power lasers. Usually pulsed (down to fractions of a nanosecond) .
III. Nd:Glass Laser
§6.1 Solid State Lasers
11/24
3/24 IF μm06.1
9/24
3/24 IF 0nm92
13/24
3/24 IF μm37.1
32ONdOptical glass doped with
3Nd
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.
IV. Ti:Sapphire Laser
§6.1 Solid State Lasers
323 OAl:Ti Four level system
3Ti
-1cm220
2g2 T
g2 E
-1cm1601180nm~660nm
nm7900
Mode-locked oscillators 10 femtoseconds and a few picoseconds, average output power of 0.5 to 1.5 watt
Chirped-pulse amplifiers
20 to 100 femtoseconds, At 5 mJ in 100 femtoseconds, the peak power of such a laser is 50 gigawatts
Tunable continuous wave lasers
Spectroscopy, LIDAR, research. This material is often used in highly-tunable mode-locked infrared lasers to produce ultrashort pulses and in amplifier lasers to produce ultrashort and ultra-intense pulses
§6.1 Solid State Lasers
§6.2 Gas Lasers
Types of gas lasers:
Advantage of gas lasers:
atom, molecular, ion
1. Wide spectral range, from sub milimeter to ultraviolet,
even X
ray or Gama ray;
2. Very good beam quality;
3. High power output;
4. High transfer efficiency (25%).
Pumping source: mostly electric discharge and aided with some assistant gases
But usually with big size
I. He-Ne Laser
§6.2 Gas Lasers
He-Ne lasers are normally small, with cavity lengths of around 15 cm up to 0.5 m, and optical output powers ranging from 1 mW to 100 mW. Apply to interferometer, holography, spectroscopy, barcode scanning, alignment, optical demonstrations.
S1
13S2
He
01S2
01 S1
P2
P3S2
S3
01SNe
共 振 转 移
电
子
碰
撞
激
励 自 发 辐
射
管 壁 效 应 弛 豫
632.8nm
μm15.1
μm39.3
Four level system
§6.2 Gas Lasers
II. CO2 Laser
Four level system
The CO2 laser can be constructed to have CW powers between mW and hundreds of kW. It is also very easy to actively Q-switch a CO2 laser by means of a rotating mirror or an electro-optic switch, giving rise to Q-switched peak powers up to GW of peak power. It can be applied to material processing (cutting, welding, etc.), surgery.
-118cm~E
0000
μm6.10μm6.9
0100 0200
0010
1000
碰 撞
碰 撞
碰 撞
0V
1V
2CO 2N
§6.2 Gas Lasers
III. Ar+ Laser
Four level system
4P3 Ar+ 基态
Ar+ 基态5P3
S5P3 4
S4P3 4
P4P3 4D4P3 4
D3P3 4
Argon lasers emit at several wavelengths through the visible to ultraviolet: 351 nm, 454.6 nm, 457.9 nm, 465.8 nm, 476.5 nm, 488.0 nm, 496.5 nm, 501.7 nm, 514.5 nm, 528.7 nm 。 It can be used to Retinal
phototherapy (for diabetes), lithography, confocal microscopy, spectroscopy pumping other lasers 。
§6.3 Organic-Dye Lasers
Organic-dye laser can overcome damage point and heating problem in the solid state laser system
Pumping source: usually pumped by flash lamp or other lasers
单态三重态
2S
1S
0S
2T
1T
Research, spectroscopy, birthmark removal, isotope separation. The tuning range of the laser depends on which dye is used
Wavelength range from 300nm to 1200nm, continuous tunable, suitable for mode-lock operation, very narrow pulse width.
§6.3 Organic-Dye Lasers
§6.4 Novel Lasers
I. Excimer Laser
The wavelength of an excimer laser depends on the molecules used, and is usually in the ultraviolet. It can be applied to Ultraviolet lithography for semiconductor manufacturing, laser surgery, LASIK.
Pumping source: fast electric discharge and electron beam
准分子是一种在激发态能够暂时结合成不稳定分子,而在基态又迅速离解成原子的缔合物。
§6.4 Novel Lasers
II. Free Electron Laser
The free-electron laser is pumped by a relativistic electron beam, has
the widest frequency range of any laser type, and can be widely
tunable, currently ranging in wavelength from microwaves, through
terahertz radiation and infrared , to the visible spectrum, to ultraviolet,
to X-rays. It has very high energy transfer efficiency (ideally 50%).
It can be used to atmospheric
research, material science,
medical applications, etc.
相对论电子通过周期变化的磁场或电场时会产生相干辐射,这种辐射为韧致辐射,其频率取决于电子的速度。
§6.4 Novel Lasers
III. Chemical Laser
A chemical laser is a laser that obtains its energy from a chemical reaction. Chemical lasers can achieve continuous wave output with power reaching to megawatt levels. They are used in industry for cutting and drilling, and in military as directed-energy weapons.
Pumping methods
1. Optical ignite
2. Electric ignite
3. Chemical ignite
4. Thermal ignite
EBCA
CAB*
反应过程
能量
1. 波长丰富2. 化学能直接 转化成激光3. 高功率输出