“LASERS”
Light Amplification by the Stimulated Emission of Radiation
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--CO2 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 50th 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
Light Amplification by the Stimulated Emission of Radiation
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” ….. Laser Speckle
(random interference pattern)
Dr. Mike Nofziger 2010
“LASERS” ….. Fundamental Parts
"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)"
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
- Needs 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” ….. Example: Red laser pointer
Dr. Mike Nofziger 2010
“LASERS” ….. Example: Red laser pointer
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
Dr. Mike Nofziger 2010
“LASERS” ….. Example: Green laser pointer
λ = 532 nm
5mW beam
Dr. Mike Nofziger 2010
“LASERS” ….. Example: Green laser pointer
Diode-Pumped Solid State “DPSS laser”
- 808nm (near-infrared) pump diode laser 808nm energy converted to 1064nm
by the Nd:YVO4 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
Dr. Mike Nofziger 2010
“LASERS” – Red vs. Green
Reference:
“Sam’s Laser FAQ”
Dr. Mike Nofziger 2010
“LASERS” – Red, Green and now Blue!
λ = 405 nm
“blue”
P = 150 mW
λ = 532 nm
“green”
P=50mW
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”
Laser Cutting
http://en.wikipedia.org/wiki/File:Lasercutting-video.ogg
Laser Welding
CO2, Nd:YAG
E ≈ 1MW/cm2
beam < .5mm
carbon steel,
stainless steel,
aluminum, http://en.wikipedia.org/wiki/File:Remote_Fibre_Laser_Welding_WMG_Warwick.ogg
titanium
top: CAD model
bottom: laser-cut part
- 0.5mm thick stainless steel
Dr. Mike Nofziger 2010