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