realignment of a q-switched nd:yag laser - … alignment of a q-switched nd:yag laser 1. principles...
TRANSCRIPT
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From-Scratch Alignment of a Q-Switched Nd:YAG Laser
1. Principles of a Q-Switched Laser2. Cavity construction and choices3. Alignment procedure4. Results
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Q-Switch Basicso Fast Q-switchingo Slow excitation
mechanism
o Inherently pulsedo “Giant Pulse” – very high
intensity
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Gain Mediumo Nd:YAG is the textbook 4-
level laser exampleo Solid state: broad energy
band N3o Slow N2 decay + Fast N1
decay: large inversion with long lifetime
o Flashlamps used for excitation
Insert picture from Milloni and Eberly
here.(p.304 or p.415?)
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Q-Switcho Pockels Cell & Polarizero Cell: Voltage controlled
waveplateo λ/4: End mirror? λ / 4
λ / 4 pol.
pol.
o λ/2: Transparent to the cavity
o Optic axis must be aligned properly!
λ / 2
λ / 2
pol.
pol.
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Resonator ChoicesoUnstable Resonator design
Low gain: build intensity from many passesHigh gain: few passes, fill medium with mode
oTotal reflector: convexoDiffraction spot output coupler, flat
mirror (?)
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Alignment Methodso Clean up output modeo Lather, Rinse, Repeat.
o Pre-align the mirrorso Pre-adjust the pitch
and yaw of the Pockels cell
o First round of threshold and holdoffadjustments
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Pre-adjustmento HeNe: rough position for
the mirrors.
o Berry’s “black sandwich”o Crossed polarizers across
a birefringent crystal (the Pockels cell)
o Yields orientation of optic axis of crystal
Image taken from http://www.olympusmicro.com/primer/techniques/polarized/polarizedintro.html
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First Threshold/Holdoffo Holdoff: maximum
lamp energy before Pockels cell “leaks”
o Threshold: minimum lamp energy to see lasing
o The cavity must be aligned to the cell…o …and the cell must be aligned to the cavity.o Iterative alignment procedure: adjust the cell for
both threshold and holdoff, then the cavity, then the repeat.
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Output modeo Post-It Notes™ have
many uses… infrared will slightly burn the glue…
o Normal incidence on output coupler →Poisson spot
o Mode is important!o Improve the mode slightly, but be careful!o Holdoff extremely sensitive to mirror alignment;
avoid large power output in breakthrough mode
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Final Threshold/Holdoff
Sadly, I wasn’t able to construct a least squares fit to the data as recorded. I did guess & check a Gaussian pulse till it looked like it fit;Each blue pulse has a FWHM of 3.22 ns.
ns
arbi
trary
inte
nsity
uni
ts
Verified as reflectionsfrom walls
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Final Threshold/Holdoff
Sadly, I wasn’t able to construct a least squares fit to the data as recorded. I did guess & check a Gaussian pulse till it looked like it fit;Each blue pulse has a FWHM of 3.22 ns.
ns
arbi
trary
inte
nsity
uni
ts
Verified as reflectionsfrom walls
![Page 12: Realignment of a Q-Switched Nd:YAG Laser - … Alignment of a Q-Switched Nd:YAG Laser 1. Principles of a Q-Switched Laser 2. Cavity construction and choices 3. Alignment procedure](https://reader031.vdocuments.net/reader031/viewer/2022021818/5aa92eb47f8b9a9a188c823f/html5/thumbnails/12.jpg)
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Final Threshold/Holdoff
Sadly, I wasn’t able to construct a least squares fit to the data as recorded. I did guess & check a Gaussian pulse till it looked like it fit;Each blue pulse has a FWHM of 3.22 ns.
ns
arbi
trary
inte
nsity
uni
ts
Verified as reflectionsfrom walls
![Page 13: Realignment of a Q-Switched Nd:YAG Laser - … Alignment of a Q-Switched Nd:YAG Laser 1. Principles of a Q-Switched Laser 2. Cavity construction and choices 3. Alignment procedure](https://reader031.vdocuments.net/reader031/viewer/2022021818/5aa92eb47f8b9a9a188c823f/html5/thumbnails/13.jpg)
13
Final Threshold/Holdoff
Sadly, I wasn’t able to construct a least squares fit to the data as recorded. I did guess & check a Gaussian pulse till it looked like it fit;Each blue pulse has a FWHM of 3.22 ns.
ns
arbi
trary
inte
nsity
uni
ts
Verified as reflectionsfrom walls
![Page 14: Realignment of a Q-Switched Nd:YAG Laser - … Alignment of a Q-Switched Nd:YAG Laser 1. Principles of a Q-Switched Laser 2. Cavity construction and choices 3. Alignment procedure](https://reader031.vdocuments.net/reader031/viewer/2022021818/5aa92eb47f8b9a9a188c823f/html5/thumbnails/14.jpg)
14
Final Threshold/Holdoff
Sadly, I wasn’t able to construct a least squares fit to the data as recorded. I did guess & check a Gaussian pulse till it looked like it fit;Each blue pulse has a FWHM of 3.22 ns.
ns
arbi
trary
inte
nsity
uni
ts
Verified as reflectionsfrom walls
![Page 15: Realignment of a Q-Switched Nd:YAG Laser - … Alignment of a Q-Switched Nd:YAG Laser 1. Principles of a Q-Switched Laser 2. Cavity construction and choices 3. Alignment procedure](https://reader031.vdocuments.net/reader031/viewer/2022021818/5aa92eb47f8b9a9a188c823f/html5/thumbnails/15.jpg)
15
Final Threshold/Holdoff
Sadly, I wasn’t able to construct a least squares fit to the data as recorded. I did guess & check a Gaussian pulse till it looked like it fit;Each blue pulse has a FWHM of 3.22 ns.
ns
arbi
trary
inte
nsity
uni
ts
Verified as reflectionsfrom walls
![Page 16: Realignment of a Q-Switched Nd:YAG Laser - … Alignment of a Q-Switched Nd:YAG Laser 1. Principles of a Q-Switched Laser 2. Cavity construction and choices 3. Alignment procedure](https://reader031.vdocuments.net/reader031/viewer/2022021818/5aa92eb47f8b9a9a188c823f/html5/thumbnails/16.jpg)
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ReferencesLasers, Peter Milonni and Joseph Eberly, (Wiley, 1988).Introduction to Modern Optics, Grant R. Fowles, (Dover, 1989)http://www.olympusmicro.com/primer/techniques/polarized/polarizedintro.htmlhttp://www.dctech.com/eureka/short-stories/poisson.php