overview of recent work on laser excitation of positronium...

OVERVIEW OF RECENT WORK ON LASER

EXCITATION OF POSITRONIUM FOR THE

FORMATION OF ANTIHYDROGEN

Pauline Yzombard(1), on behalf of the AEgIS(2) collaboration

(1) Laboratoire Aimé Cotton, Bâtiment 505, Orsay, France(2) AD-6: AEgIS, C.E.R.N. Route de Meyrin 385, 1217 Meyrin, Switzerland

g ?

Anti-Apple

Earth

g ?

OUTLINE

I. AEgIS experiment

II. Positron and laser systems

III. Recent works

Ps(n=3) laser excitation

Ps Rydberg

IV. Future works: toward a colder 𝐻 beam

MARCH 9 - LEAP 2016 - PAULINE YZOMBARD

2

CERN

Czech Technical

University

ETH Zurich

University of

Genova

University of

Milano

University of

Padova

University of

Pavia

University College

London

Politecnico di

Milano

Max-Planck Institute

Heidelbert

Institute of Nuclear

Research of the

Russian Academy

of Science

University of

Bergen

University of

Bern

University of

Brescia

Heidelberg

University

University of

Trento

University of

Paris Sud

University of

Oslo

University of Lyon 1

INFN sections of:

Genova, Milano,

Padova, Pavia,

Trento

Stefan Meyer Institute

I. AE IS COLLABORATIONg

I. AEGIS

ANTIMATTER EXPERIMENT: GRAVITY, INTERFEROMETRY, SPECTROSCOPY

Main goal: Measurement of g with 1% precision on antihydrogen.

Challenges:

- Production of a bunched cold beam of antihydrogen

- Measurement of vertical beam deflection (10 μm drop over 1 m)

via moiré deflectometer.


4

g ?

Anti-

Apple

Earth

moiré

deflectometer

e+

Ps convertor

p trap

Cf. Talk of Daniel Krasnicky

Overview of latest results from AEgIS

Aghion, S. and al. Nat. Commun vol 5 4538 (2014)

I. AEGIS - PRINCIPLE

Anti-hydrogen formation via Charge exchange process with Ps*

Principle demonstrated by ATRAP collaboration

Ps* produced via Cs* collisions on positrons trapped plasma

C. H. Storry et al., Phys. Rev. Lett. 93 (2004) 263401] 93 (2004) 263401

Interests:

Pulsed H production (time of flight – Stark acceleration)

Narrow and well-defined H n-state distribution

Colder production than via mixing process expected


5

Rydberg Ps*

Long lifetime + large cross section

σ≈ 𝑎0𝑛4

→ H formation enhanced

II. POSITRON AND LASER SYSTEMS - POSITRON SYSTEM


6

AEgIS zone

Positron system

Efficient transfer of positrons into the main traps - cfTalk of Daniel Krasnicky Overview of latest results from AEgIS

Studying positrons and Positronium physics in a dedicated test chamber

II. POSITRON AND LASER SYSTEMS - POSITRONIUM FORMATION

7Mariazzi S et al., Phys. Rev. B 2010, 81, 235481

PbWO4

Sketch of the e+ system - parameters given for 2015

22Na 11mCi

3 104 e+ / 0.15s

7 108 e+ / 3min 3.3keV e+

bunch implanted

SEM image: Silica-based nano- porous target

II. POSITRON AND LASER SYSTEMS - POSITRONIUM FORMATION

8

SSPALS (single shot positron

annihilation lifetime spectroscopy)(*)

measurements –

Average of 10 single shots.

S. Aghion et al. Nucl. Instru. Meth. in

Phy. Res Sect. B 362:86 92, 2015.

(*)Cassidy D B et al., NIMB 2007, 580, 1338

Production of Ps in the test chamber

3.3keV

Ps formation sketch

τ = 142ns

II. POSITRON AND LASER SYSTEMS - LASER SYSTEM


9

~1700 nm

Ps

Internal

energy

n=1

n=2

n=3

n Rydberg

≈ 15 − 20

continuum

205 nm

A dedicated laser system:conceived to be broadband σ ~110GHz

- to cover Doppler broadening and

magnetic mixing (Zeeman effect, at 1 T)

inside the main trap

In front of the test chamber:

Energy 60µJ, pulse 2ns, waists 6mmx8mm

In front of the test chamber:

Energy 1.3mJ, pulse 4ns, waist 10mm

III. RECENT WORKS- POSITRONIUM = 3 LASER EXCITATION

MARCH 9 - LEAP 2016 - PAULINE YZOMBARD10

n

S(%)=(Area laser OFF−Area laser ON)

Area laser OFF

1064 n

m

Ps

Internal

energy

n=1

n=2

n=3

continuum

205 nm

Aghion S et al., PRA, submitted Feb.2016

Test chamber

photo-

ionization

n=3 excitation + photoionization

EM conditions:

B = 250 Gauss

E = - 600 V/cm

e+

Gamma detector

Si02 nano-

porous targeto-Ps

cloud

preliminary

III. RECENT WORKS- POSTRONIUM = 3 LASER EXCITATION


11

n

Scan of the n=3 transition

-3P excitation line centered

at 205.05±0.02 nm

- excitation-ionization

S(%) laser at resonnace ≈ 15.5%


- From this measurement:

We extrapolate an average

temperature of the excited

o-Ps : T ~1300K ± 200 K

(Doppler broadening)

- e+ implantation energy 3.3keV

- Target at room temperature

preliminary

Predicted: 205.0474 nm

III. RECENT WORKS- POSITRONIUM RYDBERG EXCITATION (VIA =3 STATE)


12

n

Scan of the Rydberg transitionsRydberg excitation(n=1 →n=3 → 𝑛 = 15 transition)

Ps

Internal

energy

n=1

n=2

n=3

205 nm

1680 nm

-

1710 nm

n Rydberg

≈ 15 − 20


preliminary

preliminary

continuum

n=15n=16

n=17

IV. FUTURE WORK –TOWARD COLDER 𝐻


13

- Sympathetic Cooling of 𝑝 with laser cooled anions

Atomic anions studied: Os-, La

-

An alternative project: laser cooling of molecular anions, as C2-

P. Yzombard et al. Phys. Rev. Lett. 114, 213001

IV. FUTURE WORK - TOWARD A POSITRONIUM LASER COOLING ?


14

- Focusing Ps beam – via Doppler cooling

Laser focusing

Improving the 𝐻 formation = having a better solid angle


MARCH 9 - LEAP 2016 - PAULINE YZOMBARD15

- Focusing Ps beam – via Doppler cooling

Ps

Internal

energy

n=1

n=2

n=3

continuum

243 nm

1S

2P

Challenge: short Ps lifetime (~142ns)

Interest: lightest atom (µ =2 me)

implies a huge recoil energy for each scattered

photon (~1500m/s or 0.3 K)

Laser development: a long pulse 243nm has to

be implemented

(pulse ~30ns to 200ns)

Probing time

Probing time

Probing time

Probing time


MARCH 9 - LEAP 2016 - PAULINE YZOMBARD 16

-1D Doppler cooling ?

Ps

Internal

energy

n=1

n=2

n=3

continuum

243 nm

1S

2P

Simulations:

Ps 1D velocities distributions,

probed for different timing

during laser cooling – B = 0 T.

Ps velocities distributions (m/s) – 1D

PL wL ΓL δL T 3D(Ps

cloud)

5000W 7mm 50GHz 2.5cm-1 1000 K

Simulation parameters

Velocities range

excited by laser

Legend:

CONCLUSION AND OUTLOOK

Recent works in Ps physics:

First measurements of n=3 Ps laser excitation

Proof of Rydberg excitation with our dedicated laser system – major step to form 𝐻via charge exchange process

Future developments for laser works:

getting a colder 𝑝 plasma (sympathetic cooling via cold anions)

or/and focusing Ps beam (Doppler cooling)


THANK YOU FOR YOUR ATTENTION


APPENDIX

Simulation code

Anions laser cooling


Algorithm - simulations

PHYSICAL REVIEW A 69, 063806 (2004)

Absorption-emission processes calculated using rate equations

-> taking account : Laser detuning d, linewidth Glaser, saturation and

Doppler effects.

G= 1/lifetime = natural linewidth

Glaser (FWMH) Total linewidth Gtot = G+ Glaser+Gf+Ge

d

WRabi

(h/2p)WRabi=-<e|qer|f>Elaser

r

I = e0c Elaser2/2=2 Power/(p waist2)

f

e

Einstein Rate equations

Rate

Absorption

Ge

Gf Lf

Le

=> Kinetic Monte Carlo + Verlet

Solve exactly the rate equations.

Better than standard (Metropolis)

Monte Carlo P(t+dt)~P(t)+G dt

Verlet algorithm to drive the particles motion

Internal state (population) KMC

External state (position) Verlet

-All levels and transitions needed (n=1->n=2)

-gravity, magnetic field and recoil photons

-Dipole moment aligned on local field local laser polarization.

Algorithm - simulations

Anions cooling ?

Cooling Os- ?

Cooling La- ?

=> Heidelberg, Ger.

A. Kellerbauer

Cooling C2- ?

22

C2-

Studied Molecules: Candidate ?electrons

C2- Sisyphus cooling

Cooling C2- - several simulations in Penning traps.

24

Penning-like trap

configuration

P. Yzombard et al. Phys. Rev. Lett. 114, 213001

overview of recent work on laser excitation of positronium...

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