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