1. Lecture 19 Inelastic Light Scattering (Raman) cont. Photon Statistics
Read: FQ5

2. Quantum Photonics Seminar This week
THURSDAY, March 31, 2016
10:30 A.M.
ROOM EE 317
Dr. Luca Sapienza
University of Southampton (United Kingdom)
Quantum photonics on a chip: controlling light at the single photon level

3. Light scattering
(elastic)
(inelastic)
(values for optical fibre)

4. Brillouin Scattering
(raman)
(Brillouin)

5. Lattice Absorption (Light-Phonon interaction)

6. Raman Spectroscopy Molecular vibration (vibron)
C.V.Raman
1928
Molecular vibration (vibron)
Solid lattice vibration
(phonon)
citatio
Molecule “fingerprint”..
Also for nanomaterial
& solids

7. i o Cg Vg Our Instrument:
Confocal Raman Microscope+Scanning Stage+Optical Microcryostat with Electrical Feedthrough
(a)
(1)
(2)
(b)
(3) i o
 =io
Motivation?
Horiba Xplora (Raman/fluorescence)
Sample stage/micro-optical-cryostat
[T=4K--~800K; variable pressure/gas;
electrical feedthroughs for gating/transport]
(3) Scanning stage (Raman mapping/imaging) Cg Vg
I, V
Versatile, non-invasive technique, can be applied to many other nano/2D materials

8. Raman Spectrum of GrapheneD G 2D
(phonon)
=532nm
Ferrari et al’06
15:30

9. Raman spectrum sensitive to many parameters…
Thickness (layer number) & stacking
 identify graphene
Disorder (lattice defects)
Temperature (thermometer)
Strain & Crystal orientation
Doping and other electronic properties
(e-phonon coupling)
2D (G’) peak
Raman
mapping
D peak
I. Calizo, et al., " Nano Letters, 7: 2645 (2007)
Ferrari et al’06
Reviews: L.M. Malard et al., Physics Reports, 473, (2009);
Isaac Childres et al., Raman Spectroscopy of Graphene and Related Materials,
in New Developments in Photon and Materials Research, ed. Nova   (2013)
Yong P. Chen, in Horiba Readout ‘2015

10. Spectroscopic Raman (ID) imaging of graphene single crystals & grain boundaries
Q. Yu & L. Jauregui et al. Nature Mater. 2011

11. Graphene-plasma interaction: a case study of how oxygen plasma modifies graphene
(can apply to other 2D materials and plasmas/irradiations  functionalize/modify materials)
radiation/material interaction: may benefit radiation-hard electronics and radiation sensor
O plasma effects on graphene:
Etching and defect generation
Induce Raman D peak
Suppress Raman 2D (G’) peak
Raman spectrum
AFM
Graphene subject to O plasma
I. Childres et al. New J. Phys. (2011) [selected as NJP highlights in 2011]

12. Thermal Conductivity: Electro-Raman Measurement
suspended graphene
electric heating (only graphene):
well controlled/defined
Raman thermometry: reads graphene T
[Balandin’07]
SiO2
Silicon p++
532 nm Laser
Graphene
Cr/Au
Current
10μm
Variable T (4-800K)
k~2000W/mK
κ = RI2L/ (8ΔTWh)
Joule
heating
T rise
(read by Raman)
L.A. Jauregui et al. (2010); ECS Trans. (2010)
cf also Cai et al Nano Lett.10

13. Raman spectrum depends on carrier density/fermi energy in graphene
Related to/probe electron-phonon coupling & “Kohn anomaly”;
Also a manifestation of breakdown of adiabatic Born-Oppenheimer
G peak
(VG>VD
n-doping)
Dirac point
(charge neutral)
The position of this G peak is very sensitive to carrier density as shown in this PRL paper by Jun Yan. The blue points show the G band position as a function of charge density. Similarly, the 2D/G ratio is also sensitive to carrier density. Lower carrier density will give…
(VG<VD
p-doping)
Das et al.,
Nature Nanotechnology
3, 210 (2008)
Yan et al.,
Physical Review Letters
98, (2007)

14. Raman spectra of twisted bilayer graphene (tBLG)
Resonant enhancement Raman when photon energy matches
van Hove singularity (vHS) --- sensitive to twisting angle (band astructure)
CVD tBLG
G: Also Zettl et al, Park et al’12
R.He & T-F. Chung et al. Nano Lett.’13
First observation of layer-breathing mode (ZO’) – molecular like

15. Quantum Optics of Photons
FQ’Chap5
FQ’Chap6
Chap 7-8: coherent, squeezed, & number states

16. Photon Statistics FQ’Chap5 Single photon detector:
PMT (photomultiplier tube)
APD (avalanche photodiode)

17. How many photons (detected)?

18. Coherent Light: Poisson Photon Statistics

20. Classification of Light by Photon Statistics
(Nonclassical light)

21. Superpoissonian Light
1) Thermal Light (blackbody)
Classical (Rayleigh-Jeans)
Planck (quantum):

22. (focus on one mode)
Particle (Photon)
“wave noise”

23. (Superpoissonian) 2. “Chaotic” (partially coherent light)
Measurement time T (smaller) vs. c

24. Subpoissonian Light But: any (random) loss will randomize the photons
(det. Subpoissonian challenging)