State Scientific Center of the Russian Federation

National Research Institute for Physical-Technical and Radio Engineering Measurements

Progress in deep laser cooling of Strontium at VNIIFTRI

S. Strelkin, A. Galyshev, O. Berdasov, A. Gribov, S. Slyusarev

P.N. Lebedev Physical Institute of the Russian Academy of Science

K. Khabarova, N. Kolachevsky

GLONASS accuracy has significantly improved over last five years

GLONASS Accuracy

2006 2007 2008 2009 2010 20110

5

10

15

20

25

30

35

40

45

50 Anticipated (in 2002) Obtained Anticipated (in 2008)

2.85.5

7.0

12.4

2.5

8.2 6.5

12.8

16.5

35.0

5.08.0

10.0

20.0

30.0

m50.0

8 years ago GLONASS allowed one to choose the appropriate street from the list…

3 years ago one knew exactly what the street it was.

Frequency standard’s evolution

M. Takamoto et al., PRL 102, 063002 (2009)

1D optical lattice and magic wave lengths

“An optical lattice clock with accuracy and stability at the 10-18 level”, B.J.Bloom etc., Nature, vol 506, 6 Feb. 2014

Sr-87 optical lattice clock instability

Sr-87 optical lattice clock in Russia

2010 – Sr lattice clock project within GLONASS program has been started at VNIIFTRI

2011 – collaboration with P.N. Lebedev Physical Institute

Sr isotopes: 88 (81%), 87 (7%), 86 (10%), 84 (2%)

Natural linewidth = 1 mHz (allowed by hyperfine coupling of 3P0 to 3P1 and 1P1) @ 698 nm

Weak sensitivity to the magnetic field (J = 0 →J = 0 transition)

Clock transition: 1S0 3P0

Sr electronic level diagram

S r sou rce

Zeem an s low er Trap

3D scatch of the vacuum system

Vertical set method of the system

Optical scheme

detectionbeam

Silver mirror

Zeeman slowerbeam

MOT beams

oven

PMT

Zeeman slower camera

Without repumpers

With repumpers

~106

~4x107

First stage cooling

x10 more atoms with repumpers

-2.0 -1.5 -1.0 -0.5 0.0

0.0

0.2

0.4

2 мс

1= 24 m s

время сt, []

с лазерам и перекачки

без лазеров перекачки

коли

чест

воат

омов

,10[

]8

=360 m s

tim e, [s]

m s

ato

ms

num

ber

Repumping effect on trapped atoms number

Number of atoms in the “blue” MOT N~4*107

Т ~ 3 мК (depends on the intensity)

1 cm

Temperature and number of atoms in the 1st MOT

Narrower transition 1S0 3P1

is well-suited to Doppler cooling (@689 nm, natural linewidth 7,5 kHz, Doppler limit 200 nK)

Narrow line requires narrow laser spectrum and high frequency stability

Second stage cooling

Toptica DL pro laser system @689 nm

Narrowing of the red MOT cooling laser

The distance covered during transportation - 60 km

ULE systems manufacturing and transportation

modulation 20 MHzGSERVO

LD

fast

slow

AOM

AOMPDwavemeter

EO

M

PD l/4

Laser stabilization

ECDL @689 Toptica DL-100 (DL-1)

ECDL @689 Toptica DL-pro (DL-2)

ULE-2

ULE-1

Frequency comb

SERVO

SERVO

PD

PD

beatnoteDL-1/DL-2

beatnoteDL-1/frequency comb

H-maser

1 1 0 10 0 1000

10 -14

10 -13

êðèâàÿ 1

äåâè

àöèÿ

Àëë

àíà

(íîð

ìèð

îâàí

íàÿ)

âðå ì ÿ óñðåä í å í èÿ [c ]

êðèâàÿ 2

Alla

n de

viat

ion

averaging time [s]

linear drift subtracted10 -14

1

1 0 -13

10 100 1000

Linear drift ~300 mHz/s

Beatnotes

8 10 12 14 160

20

40

60

80

10010 12 14 16 18 20 22 24 26 28

temperature ULE-1,

temperture ULE-2,

0

0

C

C

с

ULE-1 = 12

0СТ

с

ULE-2 = 27

0СТ

beat

note

freq

uenc

y D

L-1/

DL-

2, M

HZ

ULE-1 spacer: ATF films

Finesse 60 000

ULE-2 spacer: Lebedev Physics Institute

Finesse 45 000

ULE-1 and ULE-2 Critical Temperatures

FWHM=110 Hz

-3000 -2000 -1000 0 1000 2000 3000

0.16

0.14

0.12

0.10

0.08

0.06

0.04

0.02

0.00

pow

er s

pect

ral d

ensi

ty [a

.u.]

time [s]

Beatnote spectral linewidth

f0

ffrequency, [arb.u.]

Doppler line profileStabilized laser spectrum

Doppler width of 1S0-3P1 transition @3 mK ~ 2 MHz

Second stage cooling features

0( ) cos[2 ]mf t f f f t ,

FM of cooling radiation allows to deal with different velocity groups within Doppler profile

Broadband second stage cooling

частота, отн. ед[ .]

спектр лазера

доплеровскийконтур линии

f f0

laser spectrum

Doppler line profile

frequency [arb.u.]

1 mm

Broadband second stage cooling

~106

Retrapping efficiency: 8-10%

Temperature in the end of broadband cooling: T~35 K

Broadband second stage cooling

Retrapping efficiency

0.05 0.10 0.15 0.20 0.25 0.30

0.03

0.04

0.05

0.06

0.07

0.08

0.09

коэф

фиц

иент

пер

езах

вата

I/Isat

High intensity in the first stage cooling leads to low retrapping efficiency

BUT

Num

ber o

f ato

ms

in s

econ

dary

MO

TRetrapping efficiency

The number of atoms in the first MOT depends on the cooling

light intensity

f0ffrequency, [arb.u.]

Doppler line profileafter broadband cooling

Stabilized laser spectrum

Atomic cloud in the end of the second stage cooling

T=2 K

N=105

Single mode second stage

f=100

Clock laser systems

0 5 0 1 00 1 50 2 00

-0 .0 4

-0 .0 2

0 .0 0

0 .0 2

0 .0 4

0 .0 6

0 .0 8

0 .1 0

tim e , s

сигн

ал,

В[]

M ode T E M 00tim e response s 21 ,7

sign

al, V

Target instability 1*10-15Finesse: 260 000Achievable laser linewidth: ~1 Hz

Clock laser systems

• First stage cooling of 88Sr and 87Sr

• Two ULE stabilized lasers for second stage cooling are assembled and characterized

• Second stage cooling of 88Sr

• Two ULE stabilized laser systems for clock transition spectroscopy are assembled

Outlook• Loading cooled atoms in the optical lattice at 813 nm and at 390

nm

• OPTICAL LATTICE CLOCK

Conclusions

Working group at VNIIFTRI

Спасибо за внимание!