Transcript Gas Laser Advantages - Kansas State University

Constructing Gas Lasers Inside of
Photonic Band Gap Fiber Optic Cells
es
Joshua Perkins
Texas A&M University
Kansas State University REU
Mentor- Dr. Kristan Corwin
PBG
PBG Fiber
Optical
Power
Meter
SMF
icer
(b)
R. Thapa et al, Opt. Express, 2006
Gas Lasers
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Well understood
Relatively cheap gain medium
Difficult to damage the gain medium
Large volumes of active material
Very Efficient
Bulky
Complex
Fragile
Diode Laser
http://en.wikipedia.org/wiki/Image:
Laser_diode_chip.jpg
http://technology.niagarac.on.ca/lasers/Chapter6.html
Outline
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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
Detailed Model
...
J12
N3
J11
v1+v3
J10
+
J9
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P13
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J12
N2
v4
J11
J10
...
J9
J13
N1
J12
J11
J 10
...
No Vibration
Rate equations
Abs.
Abs.
Stim.
Spon.
Spon.
dn3
 B13n1 I P  B23n2 I u  B32 n3 I u  A31n3  A32 n3
dt
Abs.
Stim.
Stim.
Spon.
Spon.
dn2
 B12 n1 I L  B32 n3 I u  B21n2 I L  A32 n3  A21n2
dt
Abs.
Abs.
Stim.
dn1
  B13 n1 I P  B12 n1 I L  B21n2 I
dt
Gain
 g ( )
  ( N 2  N1 )
2
8 n tspont
2
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.
Mirror
Mirror
C2H2
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
section of the
Fiber Optic Cell Cross
smallest human hairs
Splice
SM Fiber
Splice
PBG Fiber
SM Fiber
•Much less fragile
•Flexible even during lasing
•Extremely high intensities compared to
normal gas cells
•Splices between SMF and PBGF are
hard to make and are lossy
•Input and output are fiber allowing for
the use of other fiber optic devices.
•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
Variable Pressure Cavity
To pump
Pump
Gas Inlet
Mirror
Hollow
optical fiber
OC Mirror
Laser
C2H2 molecules
Polarizing 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
Output Coupler Vacuum Chamber
14cm
Screw
5cm
4cm
Bellows
5cm
Screw
XYZ Translation
4cm
Vacuum
6.75cm
Curved Mirror
Final Setup
0.59 dB
PBS
Fiber Mirror
~7.11 dB Round-trip Loss
0.83 dB
0.32 dB
R = 99%
f = 40 mm
1.87 dB
2.9 dB
(estimated)
f = 25 mm
PD
PBGF
Final Setup
Light from
Decepticon (1532
nm) Amplified by
an EDFA
0.59 dB
PBC
Fiber Mirror
~7.11 dB Round-trip Loss
0.83 dB
0.32 dB
R = 99%
f = 40 mm
1.87 dB
2.9 dB
(estimated)
f = 25 mm
PD
PBGF
What I have learned this summer
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Splicing Fibers
Fiber Optic Components
Free space optics
Optically pumped gas laser theory
Vacuum Systems
What I have done this summer
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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
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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