Transcript Solid para-H 2 - McCall Research Group

Toward a Continuous-Wave
Solid para-Hydrogen Raman Laser
for Molecular Spectroscopy
Applications
William R. Evans
Department of Physics
University of Illinois at Urbana-Champaign
Benjamin J. McCall
Departments of Chemistry, Astronomy and Physics
University of Illinois at Urbana-Champaign
Takamasa Momose
Department of Chemistry
The University of British Columbia
Outline






Motivation for the Project
Stimulated Raman Scattering
Hydrogen as a Raman Medium
Measuring the Index of Refraction of Solid
para-Hydrogen
Current Progress Toward a cw Solid
para-Hydrogen Raman Laser in the Visible
Future Plans and Summary
Mid-Infrared Spectroscopy


Many Attractive Targets in 5 – 10 μm Range
Few Available Laser Sources


Astrochemistry need sub-MHz linewidth
Need for cw sources
Possible Solution:
Solid para-H2 Raman Laser


Transparent for most of 100 nm to 10 μm
Enormous frequency shift
-1
 4155.2 cm in gas
-1
 4149.7 cm in solid
M. Fushitani, S. Kuma, Y. Miyamoto, H. Katsuki, T. Wakabayashi, T. Momose, and A.F. Vilesov, Optics Letters, 28,
1, 37 (2003)
M. Mengel, B.P. Winnewisser, and M. Winnewisser, Canadian Journal of Physics, 78, 317 (2000)
Brief Review of Raman Scattering

Pump photon scatters inelastically with an atom
 Redshifted to a “Stokes” photon.
Stimulated Raman Scattering




Two-photon process
Incoming Stokes stimulates transition
Outgoing photons emitted coherently
Efficiency of SRS depends on intracavity
power and Raman gain coefficient
Previous Work with Hydrogen
Continuous
Pulsed
Gas
Solid
Previous Work with Hydrogen
1980, 1986:
pulsed dye laser
tunable from 1-10 μm
0.2 cm-1 linewidth
Continuous
Pulsed
Gas
A. DeMartino, R. Frey, and F. Pradere, IEEE J. QUANT. ELEC., VOL. QE-16, 11 (1980)
P. Rabinowitz, B. N. Perry, and N. Levinos, IEEE J. Quantum Electron. 22, 797 (1986)
Solid
Previous Work with Hydrogen
1980, 1986:
pulsed dye laser
tunable from 1-10 μm
0.2 cm-1 linewidth
Solid
2003 – 2004:
pulsed Nd:YAG, OPO
Raman in both solid and liquid
tunable from 4.4-8 μm
0.3 – 0.4 cm-1 linewidth
Continuous
Pulsed
Gas
M. Fushitani, S. Kuma, Y. Miyamoto, H. Katsuki, T. Wakabayashi, T. Momose, and A.F. Vilesov, Optics Letters, 28, 1, 37 (2003)
B.J. McCall, A.J. Huneycutt, R.J. Saykally, C.M. Lindsay, T. Oka, M. Fushitani, Y. Miyamoto, and T. Momose, Applied Physics Letters,
82, 9, 1350 (2003)
K.E. Kuyanov, T. Momose, and A.F. Vilesov, Applied Optics, 43, 32, 6023 (2004)
Previous Work with Hydrogen
Continuous
Pulsed
Gas
1980, 1986:
pulsed dye laser
tunable from 1-10 μm
0.2 cm-1 linewidth
Solid
2003 – 2004:
pulsed Nd:YAG, OPO
Raman in both solid and liquid
tunable from 4.4-8 μm
0.3 – 0.4 cm-1 linewidth
1998 – 2002:
1-2 mW pump threshold
4 kHz linewidth
doubly-resonant cavity
F ~ 50,000
J.K. Brasseur, K.S. Repasky, and J.L. Carlsten, Optics Letters, 23, 5, 367 (1998)
J.K. Brasseur, P.A. Roos, K.S. Repasky, and J.L. Carlsten, Journal of the Optical Society of America B, 16, 8, 1305 (1999)
L.S. Meng, K.S. Repasky, P.A. Roos, and J.L. Carlsten, Optics Letters, 25, 7, 472 (2000)
L.S. Meng, P.A. Roos, K.S. Repasky, and J.L. Carlsten, Optics Letters, 26, 7, 426 (2001)
(and others)
Previous Work with Hydrogen
Continuous
Pulsed
Gas
1980, 1986:
pulsed dye laser
tunable from 1-10 μm
0.2 cm-1 linewidth
1998 – 2002:
1-2 mW pump threshold
4 kHz linewidth
doubly-resonant cavity
F ~ 50,000
Solid
2003 – 2004:
pulsed Nd:YAG, OPO
Raman in both solid and liquid
tunable from 4.4-8 μm
0.3 – 0.4 cm-1 linewidth
Tradeoff

Want:



Drawbacks:




Narrow linewidth  Need cw laser
Not high complexity  Lower finesse cavity
CW pump lasers have lower maximum power
Lower finesse cavity means less power buildup in
the cavity
Both of these factors make lasing more difficult
Tradeoff:

Need high Raman gain coefficient  Solid para-H2
Solid para-H2 Raman Gain Coefficient

Solid para-H2 Raman gain coefficient
measured by Katsuragawa and Hakuta

~ 7,000x that of gaseous hydrogen
H2 Gas
n 2.50×1020 cm-3
Γ

p-H2 Crystal
2.64×1022 cm-3
300 MHz
8.4 MHz
Narrow linewidth because solid para-H2 is a
quantum crystal
M. Katsuragawa and K. Hakuta, Optics Letters, 25, 3, 177 (2000)
Index of Refraction of Solid para-H2


To design a solid para-H2 Raman laser, we
needed to know the index of refraction of
solid para-H2.
Surprisingly, this quantity had never been
reported before.
M. Perera, et al, Optics Letters, 36, 6, 840 (March 15, 2011)
Index of Refraction of Solid para-H2
Measurement Setup


Incoming laser is refracted at slanted window.
By measuring the exit angle of the laser, we
can determine the index of the solid para-H2
using Snell’s law.
OFHC copper connected to cold head
Stainless steel cell
Laser
Sapphire
windows
M. Perera, et al, Optics Letters, 36, 6, 840 (March 15, 2011)
Index of Refraction of Solid para-H2
Results
M. Perera, et al, Optics Letters, 36, 6, 840 (March 15, 2011)
Solid para-H2 Raman Laser
Experimental Setup


With the index of refraction of solid para-H2 in
hand, we can design the setup for our laser.
1st Stage of Project:




Raman shifting in the visible: 514 nm  654 nm
Multi-mode pump laser
Singly-resonant cavity
(only building up Stokes radiation)
No active cavity locking
Solid para-H2 Raman Laser
Experimental Setup
Solid para-H2 Raman Laser
Experimental Setup
Solid para-H2 Raman Laser
Experimental Setup
Solid para-H2 Raman Laser
Cell Design

Interfaces designed to be at Brewster’s
angle.


Minimize reflective scattering losses inside cavity.
Because np-H2 is greater than 1, the windows
on the cell need to be wedged.
Solid para-H2 Raman Laser
Experimental Setup
Solid para-H2 Raman Laser
Experimental Setup
Solid para-H2 Raman Laser
Cavity Design

Specialty coated cavity
mirrors





1 m Radius of Curvature
High transmitting at pump wavelength
(T ~ 98% at 514 nm)
High reflecting at Stokes wavelength
(R = 99.5% at 654 nm)
Cavity length 50 cm
Diffraction grating used to separate pump
beam from Stokes beam after the cavity
Solid para-H2 Raman Laser
Current Progress



Solid para-H2 crystal grown
in new cell
Pump laser through the
crystal  windows properly
aligned
Raman output within the
next few weeks
Solid para-H2 Raman Laser
Future Plans




Active cavity locking
Single-mode pump laser
Doubly-resonant cavity
Raman lasing in the infrared
Summary




Solid para-H2 is an attractive material for use as a
Raman gain medium.
A fully-optimized solid para-H2 Raman laser could
potentially provide the first widely tunable laser
source for ultra high resolution spectroscopy in the
5-10 μm range.
We have made the first ever measurements of the
index of refraction of solid para-H2.
We have successfully designed and built a system
that should be able to achieve Stokes output using
solid para-H2 within the next few weeks.
Acknowledgments







Benjamin McCall
Takamasa Momose
Manori Perera
Michael Porambo
Heather Hanson
Preston Buscay The McCall Research Group
Kristin Evans