Spectroscopy of and with Laser Pointers Joel Tellinghuisen Department of Chemistry Vanderbilt...
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![Page 1: Spectroscopy of and with Laser Pointers Joel Tellinghuisen Department of Chemistry Vanderbilt University Nashville, TN 37235.](https://reader030.fdocuments.us/reader030/viewer/2022032703/56649d0c5503460f949e0bf5/html5/thumbnails/1.jpg)
Spectroscopy of and with Spectroscopy of and with Laser PointersLaser Pointers
Joel Tellinghuisen
Department of ChemistryVanderbilt UniversityNashville, TN 37235
![Page 2: Spectroscopy of and with Laser Pointers Joel Tellinghuisen Department of Chemistry Vanderbilt University Nashville, TN 37235.](https://reader030.fdocuments.us/reader030/viewer/2022032703/56649d0c5503460f949e0bf5/html5/thumbnails/2.jpg)
Start with the punch line …
[Gerstenkorn & Luc atlas (1978)]
Ordinate scale quantitative; source?
A key-chain red laser pointer (< 5$ bulk)
0.00
0.01
0.02
0.03
196.0 196.4 196.8 197.2 197.6 198.0 198.4
Ab
so
rba
nc
e
- 15000 cm-1
![Page 3: Spectroscopy of and with Laser Pointers Joel Tellinghuisen Department of Chemistry Vanderbilt University Nashville, TN 37235.](https://reader030.fdocuments.us/reader030/viewer/2022032703/56649d0c5503460f949e0bf5/html5/thumbnails/3.jpg)
Back to the beginning. What is said …Garland, Nibler, and Shoemaker (Experiments in Physical Chemistry, 7th edit.)
Expt. 39 – (Absorption and Emission Spectra of I2) — “The use of a doubled Nd:YAG laser is particularly appealing, since this is becoming increasingly available as for example a relatively inexpensive green ‘laser pointer.’ … An unseeded Nd:YAG multimode source will produce light with a width of 0.5 to 1 cm–1 so that several I2 states will be excited. This will lead to a more complex mixture of emission doublets, but this multimode source is still suitable for this experiment.”
And what you see when three different green laser pointers (GLPs) are directed through an I2 cell …
![Page 4: Spectroscopy of and with Laser Pointers Joel Tellinghuisen Department of Chemistry Vanderbilt University Nashville, TN 37235.](https://reader030.fdocuments.us/reader030/viewer/2022032703/56649d0c5503460f949e0bf5/html5/thumbnails/4.jpg)
Examine the fluorescence spectra:
Hg calibration
Fluorescence excited from
= 0 = 2 = 3
![Page 5: Spectroscopy of and with Laser Pointers Joel Tellinghuisen Department of Chemistry Vanderbilt University Nashville, TN 37235.](https://reader030.fdocuments.us/reader030/viewer/2022032703/56649d0c5503460f949e0bf5/html5/thumbnails/5.jpg)
And as excited by an Ar-ion laser:
The dispersed beams from a multiline Ar-ion laser traverse the cell.
Fluorescence excited by
Ar+ 514.5 nm GLP 532 nm
![Page 6: Spectroscopy of and with Laser Pointers Joel Tellinghuisen Department of Chemistry Vanderbilt University Nashville, TN 37235.](https://reader030.fdocuments.us/reader030/viewer/2022032703/56649d0c5503460f949e0bf5/html5/thumbnails/6.jpg)
A visual appreciation of the effects of optical depth (beam attenuation on right) and quenching (500 Torr Ar in cell on left).
![Page 7: Spectroscopy of and with Laser Pointers Joel Tellinghuisen Department of Chemistry Vanderbilt University Nashville, TN 37235.](https://reader030.fdocuments.us/reader030/viewer/2022032703/56649d0c5503460f949e0bf5/html5/thumbnails/7.jpg)
-4 -2 0 2 4
cm-1
Representative high-resolution spectra for one model of GLP, as recorded on a CCD array.
![Page 8: Spectroscopy of and with Laser Pointers Joel Tellinghuisen Department of Chemistry Vanderbilt University Nashville, TN 37235.](https://reader030.fdocuments.us/reader030/viewer/2022032703/56649d0c5503460f949e0bf5/html5/thumbnails/8.jpg)
-8 -4 0 4 8 12 16
cm-1
A
BCDE
And for two other models (A,B and C-E)
![Page 9: Spectroscopy of and with Laser Pointers Joel Tellinghuisen Department of Chemistry Vanderbilt University Nashville, TN 37235.](https://reader030.fdocuments.us/reader030/viewer/2022032703/56649d0c5503460f949e0bf5/html5/thumbnails/9.jpg)
The last of these seems to be operating single-mode much of the time, but …
Modes are spaced greater than anticipated, with pattern dependent upon GLP operating power and time.
Spectra recorded on a commercial UV-Vis (Shimadzu) at 0.1-nm resolution.
![Page 10: Spectroscopy of and with Laser Pointers Joel Tellinghuisen Department of Chemistry Vanderbilt University Nashville, TN 37235.](https://reader030.fdocuments.us/reader030/viewer/2022032703/56649d0c5503460f949e0bf5/html5/thumbnails/10.jpg)
from http://repairfaq.ece.drexel.edu/sam/laserssl.htm#sslafgl
[Sam's Laser FAQ, Copyright © 1994-2006, Samuel M. Goldwasser, All Rights Reserved.]
So why such range and complexity of mode structure?
Lots of optical surfaces in the cavity?
![Page 11: Spectroscopy of and with Laser Pointers Joel Tellinghuisen Department of Chemistry Vanderbilt University Nashville, TN 37235.](https://reader030.fdocuments.us/reader030/viewer/2022032703/56649d0c5503460f949e0bf5/html5/thumbnails/11.jpg)
651 652 653 654nm
x 100
673 674 675 676nm
By contrast, mode structure in red laser pointers (RLPs) is simple.
The two spectra in each plot below were taken for the same RLP at different times, with strong and weak batteries in one case.
![Page 12: Spectroscopy of and with Laser Pointers Joel Tellinghuisen Department of Chemistry Vanderbilt University Nashville, TN 37235.](https://reader030.fdocuments.us/reader030/viewer/2022032703/56649d0c5503460f949e0bf5/html5/thumbnails/12.jpg)
But the key-chain model showed surprisingly little side-mode emission — estimated at only ~2% in the illustrated case.
-20 -10 0 10 20 30
- 15290 cm-1
x 60
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657.0 658.0 659.0 660.0
nm
3.50 V
657.0 658.0 659.0 660.0
nm
3.79 V
657.0 658.0 659.0 660.0
nm
3.86 V(cold start)
657.0 658.0 659.0 660.0
nm
3.86 V(+ 1 min)
657.0 658.0 659.0 660.0
nm
3.86 V(+ 3 min)
657.0 658.0 659.0 660.0
nm
3.86 V(long t)
657.0 658.0 659.0 660.0
nm
4.08 V
657.0 658.0 659.0 660.0
nm
4.20 V
657.0 658.0 659.0 660.0
nm
4.34 V
657.0 658.0 659.0 660.0
nm
4.34 V
657.0 658.0 659.0 660.0
nm
4.34 V
657.0 658.0 659.0 660.0
nm
4.50 V
657.0 658.0 659.0 660.0
nm
4.50 V
657.0 658.0 659.0 660.0
nm
4.50 V
657.0 658.0 659.0 660.0
nm
4.65 V
657.0 658.0 659.0 660.0
nm
4.65 V
As for the GLPs, spectral output depends on power and time (evidently temperature). Thus each RLP is tunable and scanable.
![Page 14: Spectroscopy of and with Laser Pointers Joel Tellinghuisen Department of Chemistry Vanderbilt University Nashville, TN 37235.](https://reader030.fdocuments.us/reader030/viewer/2022032703/56649d0c5503460f949e0bf5/html5/thumbnails/14.jpg)
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 20 40 60 80 100
Ab
sorb
an
ce
t (s)
PI2 = 42 mTorr
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 20 40 60 80 100
Ab
sorb
an
ce
t (s)
PI2 =103 mTorr
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 20 40 60 80 100
Ab
sorb
an
ce
t (s)
PI2 =228 mTorr
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 20 40 60 80 100
Ab
sorb
an
ce
t (s)
PI2 =380 mTorr
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 20 40 60 80 100
Ab
sorb
an
ce
t (s)
PI2 =720 mTorr
Spectroscopy with laser pointers?
Record A(t) after turning GLP off, for various PI2.
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-0.02
-0.01
0.00
0.01
0.02
0.03
0 20 40 60 80 100
Ab
so
rba
nc
e
t (s)
Minimal values of A between lines provide estimates of strength of continuum absorption (mainly C X)
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Results: Unprecedented precision in (continuum) at 532 nm.
-0.015
-0.010
-0.005
0.000
0.005
0.010
0.015
0 1 2 3 4
Abs
orba
nce
[I2] (10-5 mol/L)
= 84.4(1.5) L mol -1 cm-1
![Page 17: Spectroscopy of and with Laser Pointers Joel Tellinghuisen Department of Chemistry Vanderbilt University Nashville, TN 37235.](https://reader030.fdocuments.us/reader030/viewer/2022032703/56649d0c5503460f949e0bf5/html5/thumbnails/17.jpg)
Similar experiments with RLP: Now we can also estimate B X transition strength from integrated lines. Pick strong doublet near 15 308.4 cm–1 [P94 in 6-5 band and R85 in 4-4]
0.00
0.01
0.02
0.03
0.04
0.05
0.06
0.07
8.3 8.4 8.5 8.6 8.7 8.8 8.9 9.0 9.1
Abs
orba
nce
- 15 300 cm-1
0.000
0.005
0.010
0.015
0.000
0.001
0.002
0 1 2 3 4 5
Abs
orb
anc
e Are
a (cm-1)
[I2] (10-5 mol/l)
= 36.84(21)
|e|2 = 1.220(13) D 2
![Page 18: Spectroscopy of and with Laser Pointers Joel Tellinghuisen Department of Chemistry Vanderbilt University Nashville, TN 37235.](https://reader030.fdocuments.us/reader030/viewer/2022032703/56649d0c5503460f949e0bf5/html5/thumbnails/18.jpg)
10000
12000
14000
16000
18000
20000
22000
24000
2.00 2.50 3.00 3.50 4.00 4.50 5.00
X(0g+)A'(2u)
A(1u)
B(0u+)
C1(1u)
R (Å)
E (cm-1) 0.4
0.6
0.8
1.0
1.2
1.4
450 500 550 600 650
|e|2 (D
2)
nm
0
50
100
150
200
500 550 600 650 700
(L
mo
l-1
cm-1
)
nm
C - X
A - X
Spectroscopy results summary …
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