Lasers

surprisesameSemiconductor

Nov 1, 2013 (3 years and 1 month ago)

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Dr. Mike Nofziger 2010

“LASERS


L
ight
A
mplification by the
S
timulated
E
mission of
R
adiation

Dr. Mike Nofziger 2010

“LASERS
” …..
small

Tunable Diode Laser


-

about 2mm x 2mm chip


-

used to measure water vapor concentration in the near
-
IR


-

used to detect

low
-
levels of gas concentration (
ppm
, ppb)

Dr. Mike Nofziger 2010

“LASERS
” …..

Large!!!

NOVA Laser at LLNL

Dr. Mike Nofziger 2010

“LASERS
” …..
History

1917
--
Albert Einstein describes the photon and points out that stimulated emission


of light could occur.


1958
--
Arthur Schawlow and Charles Townes publish their theoretical paper


"Infrared and Optical Masers" in Physical Review, 1958.


1960
--
Theodore
Maiman

invents the first laser, the optical version of the maser,


using a man
-
made ruby crystal. First operated on May 16, 1960.


1961
--
HeNe

gas laser is invented by Ali
Javan
, et al., Bell Labs.



-
first laser to emit a continuous (CW) beam of light



-
first output was at 3.39 microns, in the
infrared





-
visible output at 0.633 microns (633 nm) in 1962



-
"workhorse of the laser industry“


1963
--
CO
2

gas laser is invented by Patel, Bell Labs.

1964
--
Argon ion laser is invented by Bridges, Hughes Research Labs.

1966
--
Organic Dye (liquid) laser is invented.

1970's
--
Semiconductor lasers are run at room temperature, paving the way for their


practical use today.

Dr. Mike Nofziger 2010

“LASERS


…..
2010, the 50
th

Anniversary!

“A

solution looking for a problem.”

http://spie.org/media/laserplayer/laserplayer.html


http://www.laserfest.org/


Dr. Mike Nofziger 2010

“LASERS


…..

Basic Principle

L
ight
A
mplification by the
S
timulated
E
mission of
R
adiation

Atoms absorb energy…


A population inversion is created…


The atoms

return to their non
-
energetic states by emitting radiation

(“light”
--
UV, visible, or IR) through stimulated emission…


Feedback in an optical cavity amplifies this light…


Some of this light is emitted in the form of laser light!

Dr. Mike Nofziger 2010

“LASERS


…..

Stimulated Emission

Dr. Mike Nofziger 2010

“LASERS


…..

Characteristics of Laser Light

Dr. Mike Nofziger 2010

“LASERS


“LASERS


…..

Laser Speckle


(random interference pattern)

Dr. Mike Nofziger 2010

"How to Make a Laser"




"Gain medium (to provide for population inversion)"

+

"Input source of energy (electricity, light, etc.)"

+

"Resonant cavity (provides optical feedback and
sustains stimulated emission)"



“LASERS


…..

Fundamental Parts

Dr. Mike Nofziger 2010

“LASERS


…..

Example: The Ruby Laser


The
RubyLaser






-

Sapphire

crystal doped with chromium ions (
≈ 0.05%)



-

The sapphire rod has flat, polished ends coated with gold



-

The chromium

ions absorb the input white
-
light and emit the


laser light




-

Wavelength
of
694
nm
(ruby
-
red color)




-

Output beam

is pulsed




-

N
eeds high voltage to run the flash lamp

Dr. Mike Nofziger 2010

“LASERS


…..

Example: The Ruby Laser

Dr. Mike Nofziger 2010

“LASERS


…..

Example: The Ruby Laser

Dr. Mike Nofziger 2010

“LASERS


…..

Example:
He
-
Ne Laser

Dr. Mike Nofziger 2010

“LASERS


…..

Example: He
-
Ne Laser

Dr. Mike Nofziger 2010

“LASERS


…..

Example: He
-
Ne Laser

Dr. Mike Nofziger 2010

“LASERS


“LASERS


…..

Example:
Red laser pointer

Dr. Mike Nofziger 2010

“LASERS


Red Laser Pointer

-

direct

output of red light from the Laser Diode (“LD”)


λ

= 633nm, 650nm, 670nm, etc.

-

output is monitored by the built
-
in


photodiode detector (“PD”)

-
beam expands and is collimated by the aspheric lens

“LASERS


…..

Example:
Red laser pointer

Dr. Mike Nofziger 2010

5mW beam

λ

= 532 nm

“LASERS


…..

Example:
Green laser pointer

Dr. Mike Nofziger 2010

“LASERS


Diode
-
Pumped Solid State

“DPSS

laser”

-

808nm (near
-
infrared) pump diode laser 808nm energy converted to 1064nm


by the Nd:YVO
4

crystal

-

1064nm energy converted

to 532nm green light by the KTP crystal

-

this is a non
-
linear process called “frequency
-
doubling”

-

the input frequency is doubled, and the output wavelength is cut in half

-

beam is expanded

-

beam is collimated

-

beam is filtered to block the (powerful) original IR energy at 808nm

“LASERS


…..

Example:
Green laser pointer

Dr. Mike Nofziger 2010

“LASERS



Red
vs.

Green

Reference:


Sam’s Laser FAQ


Dr. Mike Nofziger 2010

λ

= 405 nm



blue


P = 150
mW

λ

= 532 nm



green


P=50mW

“LASERS



Red,
Green
and now
Blue
!

Dr. Mike Nofziger 2010

“LASERS


…..

Example:
High
-
Power Diodes

-

Stacks

of linear arrays of diode lasers

-

100’s to kilowatts of power

-

near infrared wavelengths

-

used for materials processing

Dr. Mike Nofziger 2010

“LASERS


…..

Example: CD Diode Lasers

output in the near
-
infrared



5


50mW output

actual laser chip from a CD player

Dr. Mike Nofziger 2010

“LASERS


Laser Guide Stars


-

VLT

8.2m telescopes

-

creates an artificial star at an altitude of 90 km

-
yellow sodium line

-

part of the VLT’s Adaptive Optics system

Dr. Mike Nofziger 2010

“LASERS


http://en.wikipedia.org/wiki/File:Lasercutting
-
video.ogg


top: CAD

model

bottom: laser
-
cut part

-

0.5mm thick stainless steel

Laser Cutting

http://en.wikipedia.org/wiki/File:Remote_Fibre_Laser_Welding_WMG_Warwick.ogg


Laser Welding

CO
2
,
Nd:YAG

E ≈ 1MW/cm
2


beam

< .5mm

carbon steel,
stainless steel,

aluminum,

titanium