Post on 31-Mar-2015
Constructing Gas Lasers Inside of Photonic Band Gap Fiber Optic Cells
Joshua Perkins
Texas A&M University
Kansas State University REU
Mentor- Dr. Kristan Corwin
R. Thapa et al, Opt. Express, 2006
Gas Lasers
• Well understood• Relatively cheap gain medium• Difficult to damage the gain medium• Large volumes of active material• Very Efficient• Bulky• Complex • Fragile
http://technology.niagarac.on.ca/lasers/Chapter6.html
Diode Laser
http://en.wikipedia.org/wiki/Image:Laser_diode_chip.jpg
Outline
• How molecular gas lasers work
• Why we picked Acetylene gas
• How laser cavities work
• Our solution for better gas cells
• Our laser cavity setup and estimated losses
• My accomplishments this summer
Optically Pumped Gas Lasers
• Pump• Relaxation• Stimulated
Emission of Radiation
http://www.answers.com/topic/population-inversion-3level-png-1
P13
v1+v3
v4
No Vibration
...
J12
J11
J10
J 9
...
+
Detailed Model
...
J13
J12
J11
J 10
...
...
J12
J11
J10
J 9
N2
N3
N1
Rate equations
212 1 32 3 21 2 32 3 21 2L u L
dnB n I B n I B n I A n A n
dt
313 1 23 2 32 3 31 3 32 3P u u
dnB n I B n I B n I A n A n
dt
113 1 12 1 21 2P L
dnB n I B n I B n I
dt
Abs.
Abs.
Abs.
Abs.
Abs.
Stim.
Stim.
Stim.
Stim.
Spon. Spon.
Spon. Spon.
Gain
2
2 1 2
( )( )
8 spont
gN N
n t
2 l Alkali-vapor lasers can have gains of 2000x
CO2 is about 4% per cm and up to 200% per centimeter for pulsed CO2
Acetylene Gas
• Well understood• Quickly available• Frequency reference
measurements• Possible to produce
light in a region that works well with fiber optic equipment
Laser Cavities
• A laser cavity is simply gain medium between mirrors with some way to get energy in and photons out.
C2H2
MirrorMirror
Glass Tube
Issues:
•For more gain a longer (or wider) cavity is required, but scaling is an issue
•Pump Beam Size
•Intensity in gain medium
Fiber Optic Cell
SM Fiber SM FiberPBG Fiber
Splice Splice
•Much less fragile
•Flexible even during lasing
•Extremely high intensities compared to normal gas cells
•Input and output are fiber allowing for the use of other fiber optic devices.
•Splices between SMF and PBGF are hard to make and are lossy
•Loss is due to mode mismatching because PBG are multi mode and Single Mode are not. Also Refractive index Change
•Delicate due to fine structure being melted to the solid face of SM fiber
Cross section of the smallest human hairs
Variable Pressure Cavity
Hollowoptical fiber
Gas InletTo pump
Laser
C2H2 moleculesPolarizing Beam Splitter
•Has worked in the past
•Polarization is necessary because dichroic mirrors don’t exist for these wavelengths
•More vacuums to maintain and more free space optics to align
Mirror
Pum
p
OC Mirror
4cm5cm
14cm
Output Coupler Vacuum Chamber
4cm
Bellows
6.75
cm
Vacuum
Screw
Screw
XYZ Translation
5cm
Curved Mirror
Final Setup
PBS
Fiber Mirror
PBGF
f = 40 mm f = 25 mm
R = 99% 1.87 dB
0.32 dB
0.83 dB
0.59 dB
PD2.9 dB
(estimated)
~7.11 dB Round-trip Loss
Final Setup
PBC
Light from Decepticon (1532 nm) Amplified by an EDFA
Fiber Mirror
PBGF
f = 40 mm f = 25 mm
R = 99% 1.87 dB
0.32 dB
0.83 dB
0.59 dB
PD2.9 dB
(estimated)
~7.11 dB Round-trip Loss
What I have learned this summer
• Splicing Fibers
• Fiber Optic Components
• Free space optics
• Optically pumped gas laser theory
• Vacuum Systems
What I have done this summer
• Design of optical and vacuum systems
• Part ordering
• Building of optical and vacuum systems
• Took a project that had just cleared the proposal stage and built a functional testing apparatus.
C2H2
Buffer Gas
Summary
• How molecular gas lasers work
• How laser cavities work
• Improvement of gas cells using PGB Fibers
• Vacuum chamber and fiber lasing scheme setup
• What I learned in the REU
Future Directions
• Fluorescence Testing.
• Rate constant control with buffers
• Working all fiber gas laser
• Comparable to diode lasers for cost and size, but keeps the advantages of gas lasers
Acknowledgements
• K-State REU Program 2008 funded by NSF
• Dr. Kristan Corwin –Mentor• Dr. Larry Weaver • Andrew Jones• Kevin Knabe• Dr. Karl Tillman• Mike Wells