The Index of Refraction of The Index of Refraction of Solid HydrogenSolid Hydrogen

Lieutenant Colonel Brian Tom*, USAFLieutenant Colonel Brian Tom*, USAFSiddhartha Bhasker*Siddhartha Bhasker*

Yuki MiyamotoYuki Miyamoto‡‡

Dr. Takamasa MomoseDr. Takamasa Momose‡‡ Dr. Benjamin McCall*Dr. Benjamin McCall*††

*Department of Chemistry, University of Illinois at Urbana-Champaign*Department of Chemistry, University of Illinois at Urbana-Champaign

††Department of Astronomy, University of Illinois at Urbana-ChampaignDepartment of Astronomy, University of Illinois at Urbana-Champaign

‡‡Department of Chemistry, The University of British ColumbiaDepartment of Chemistry, The University of British Columbia

OverviewOverview

• Solid hydrogen backgroundSolid hydrogen background

• Why measure the index of refraction?Why measure the index of refraction?

• ExperimentExperiment

• ResultsResults

• ConclusionsConclusions

Solid Hydrogen BackgroundSolid Hydrogen Background

• Study of solid hydrogen is >70 years oldStudy of solid hydrogen is >70 years old– Quantum effectsQuantum effects– Spin echo/relaxation NMR propertiesSpin echo/relaxation NMR properties– Raman scattering Raman scattering

• Areas open for studyAreas open for study– Mechanical propertiesMechanical properties– Index of refractionIndex of refraction

Van Kranendonk, Solid Hydrogen, Plenum Press, 1983. Souers, Hydrogen Properties for Fusion Energy, U of Cal. Press, 75,1986.

H2

Why measure the index?Why measure the index?

• Stokes Raman shift in HStokes Raman shift in H22

– Obtain wavelengths for Obtain wavelengths for spectroscopyspectroscopy

• Can use multipass cell Can use multipass cell with Hwith H22 gas gas

– Requires high Requires high reflectivity/high damage reflectivity/high damage threshold mirrorsthreshold mirrors ω= 683 nm 953 nm 1576 nm

ν=1

ν=0

ωPump=532nm

Brasseur et al., Optics Ltrs., 23, 367, 1998. Brasseur et al., JOSA Comm., 1999. McCall et al., App. Phys. Ltrs., 82, 2003. McCall, OSU Conference Talk, 2003.

Why measure the index?Why measure the index?

• Condensed phases are Condensed phases are more efficient for more efficient for

Raman shiftRaman shift– 7000 x gain7000 x gain– Higher number densityHigher number density– Smaller line widthSmaller line width

• Consistent with Consistent with observations of observations of Katsuragawa Katsuragawa et alet al. .

PhasePhase NumberNumber

DensityDensity

(cm(cm-3-3),n),n

LinewidthLinewidth GainGain

Gaseous Gaseous HH22

3.1E213.1E21 28.4GHz28.4GHz

LiquidLiquid

HH22

2.1E222.1E22 1.5 GHz1.5 GHz

SolidSolid

HH22

2.6E222.6E22 <7 MHz<7 MHz

Souers, Hydrogen Properties for Fusion Energy, U of Cal. Press, 1986. Uetake et al., Phys. Rev. A., 61, 1999. Katsuragawa et al., Optics Letters, 25 177, 2000. McCall et al., App. Phys. Ltrs., 82, 2003.

n

Why Measure the Index?Why Measure the Index?

• Continuous wave, Stokes down-converted Continuous wave, Stokes down-converted light using solid Hlight using solid H22

Experiment:Experiment:The art of making solid hydrogenThe art of making solid hydrogen

• >99.9% pure parahydrogen used in both >99.9% pure parahydrogen used in both Kyoto and Champaign-UrbanaKyoto and Champaign-Urbana

• Two methods of crystal growthTwo methods of crystal growth– Vapor DepositionVapor Deposition– Crystallization Crystallization

from liquidfrom liquid

Souers, P.,Hydrogen Properties for Fusion Energy, U of Cal., 1986.

Experiment: KyotoExperiment: Kyoto

• 434.8 to 1111.1 nm434.8 to 1111.1 nm• Measured differenceMeasured difference

between vacuumbetween vacuum

and solid Hand solid H22

– MeasurementMeasurement

taken attaken at

10 meters10 meters

Experiment: Champaign-UrbanaExperiment: Champaign-Urbana

Experiment: Champaign-UrbanaExperiment: Champaign-Urbana

Experiment: Champaign-UrbanaExperiment: Champaign-Urbana

= Vacuum in cell

= Hydrogen in cell

Experiment: Champaign-UrbanaExperiment: Champaign-Urbana

v UU U

A v

n nA Tan ArcSin Sin ArcSin Sin

n n

v UU U

s v

n nG Tan ArcSin Sin ArcSin Sin

n n

uU U

s UU U

vUU

s

nS Sin ArcSin Sin

n nV Tan ArcSin Sin

nnCos ArcSin Sin

n

D

Wavelength (nm)Wavelength (nm) Index* Index* ++0.0010.001

(Kyoto)(Kyoto)

IndexIndex† † ++0.0010.001

(C-U)(C-U)

2000-50002000-5000 DFGDFG

1111.11111.1 1.1321.132

1000.01000.0 1.1331.133 DiodeDiode

909.1909.1 1.1331.133 DiodeDiode

833.3833.3 1.1331.133

769.2769.2 1.1331.133

714.3714.3 1.1331.133

666.7666.7 1.1321.132

632.8632.8 1.1373-1.13951.1373-1.1395

625.0625.0 1.1321.132

588.2588.2 1.1331.133

555.6555.6 1.1341.134

526.3526.3 1.1351.135

500.0500.0 1.1351.135 Argon IonArgon Ion

476.2476.2 1.1361.136 Argon IonArgon Ion

454.5454.5 1.1361.136

434.8434.8 1.1361.136

PreliminaryResults

*6 K† 7.724-8.049 K

= C-U Target

Wavelengths

Preliminary ResultsPreliminary Results

8.045 K

7.724 K

=C-U data

ConclusionsConclusions

• Solid hydrogen is an efficient tool for Solid hydrogen is an efficient tool for generating light for spectroscopy generating light for spectroscopy

• More measurements to comeMore measurements to come

• CW, Stokes-shiftedCW, Stokes-shifted

light via solid Hlight via solid H22

is on the horizonis on the horizon

AcknowledgementsAcknowledgements

• United States Air ForceUnited States Air Force

• National Science FoundationNational Science Foundation

• The Packard FoundationThe Packard Foundation

• Prof. Takeshi Oka, University of ChicagoProf. Takeshi Oka, University of Chicago