The Development of Optical Frequency Standards and its Application to Space Missions Naicheng Shen...

The Development of Optical Frequency Standards and its Application to Space Missions

Naicheng Shen

Joint Laboratory of Advanced Technology in Measurements ( 中科院计量测试高技术联合实验室 ), Institute of Physics Chinese Academy of Sciences, Beijing 100080

ASTROD Symposium 2006, July 14-16, Beijing

Outline

Motivation and Background Optical Frequency Standards 532 nm Iodine Stabilized Nd:YAG Laser Optical Frequency Comb A Method of Synchronization of Clocks Using Signals From Orbiting Satellite such as GPS


Motivation

To develop optical frequency standads

To improve on reproducibility of 532 nm iodine

stabilized Nd:YAG laser

To pursue phase control femtosecond laser

To develop optical frequency comb

To develop a new technology for synchronization of clocks


Authors Lab Atoms and transitions R /m1

Andreae et al.(1992) MPQ H ： 1S-2S 10 973 731.568 41(42)

Nez et al. (1992) LKB H ： 2S-8S/8D 10 973 731.568 30(31)

Weitz et al. (1995) MPQ H ： 1S-2S 10 973 731.568 44(31)

Bourzeix et al. (1996) LKB H ： 2S-8S/8D 10 973 731.568 36(18)

de Beauvoir et al. (1997)

LKB LPTF

H,D ： 2S-8S/8D 10 973 731.568 59(10)

Udem et al. (1997) MPQ H ： 1S-2S 10 973 731.568 639(91)


F

1 Control the carrier envelope phase offset (CEO) is a very important topics in ultrafast science and frequency metrology.

E(w,t) =E0(t)exp(iw t+f)

CEO lead to the comb shift Df =2pd /F Repetition rate f= c /2nlLongtitudinal mode frequency

fn=d+nF

Optical frequency comb

D.J.Jones et al., Science 288, 635(2000)


fs laser spetrum

Broaden the femtosecond laser spectrum to cover an octave by photonic crystal fiber (PCF).

f1=d+nF

f2=d+2nF

Heterodyne measure the beat of 2f1 an

d f2 will reveal the signal d

2 f1 - f2 = 2(nF+d) -(2nF+d ) = d


3.2 Generation of Continuum with PCF

Frequency Measurement Experimental Layoutantenna

PumpLaser

PCF

Reference 10MHzP

hase

loop

for re

petitio

n

rate

Phase

loop fo

r C

EO

Grating

532 nm iodine stabilized Nd:YAGfrequency standard

Dr R. L. Byer Groups, Stanford University, 1992•Unprecedented frequency stability: 510-14(1 s), 510-15(after 400 s) , Dr J. L. Hall Groups , JILA,1999•Frequency stability: 510-14 (relative short term), 610-15 (longer durations), BIPM, 2001•New hyperfine structure transitions and frequency stability and reproducibility had obtained exciting results at AIST•Absolute frequency measurements have been developed in several countries The accuracy and long term stability are similar to the small Cs clock of CCTV

The short term stability depend on itself

Specifications Refer to the small Cs clock (HP-5071

Optical Parts of 532nm I2-stabilized Nd:YAG Laser

532nm

1064nm

Reflection Prism

Reflection Prism

ApertureAOM

EOM

PD & pre-amplifier

Nd:YAG Laser

PBS1 /4/2 /2PBS2

PBS3

Temperature control of I2 cell

Side view

ApertureAperture

35 cm × 70 cm


Molecular Iodine Absorption Cell

3-stage cooling

quartz glass

Temperature control Cold finger

Sealed box

1.Windows are optically contacted to the tube

2.Baked and vacuumized 3 days continuously

3.Filled with highly pure iodine at AIST of Japan or JLAST,CAS, China

4.Applied 3-stage cooling 5. Using a sealed box for 6. The temperature is set ensured lower temperature isolating the cooling at - 18C, a vapor components pressure of 0.54 Pa


4.Applied 3-stage cooling 5. Using a sealed box for 6. The temperature is set ensured lower temperature isolating the cooling at - 18C, a vapor

components pressure of 0.54 Pa

Optical Extending in Lengthways and Transverse Orientation

Bigger beam diameter benefit

for increasing transverse transit time

Low vapor pressure

Narrow linewidth

Good SNR


Electrics Parts of I2-stabilized Nd:YAG Laser

Modulated probe beam

Monolithic ring laser and SHG

PD & pre-amplifier Filter and amplifier

Servo control

Slow Fast

PI control

DBMOscillatorPhase shift

EOM Driver

EOM

AOM

AOM DriveFrequency synthesizer

Rubidium clock

RFLO

IF

10MHz80MHz

Frequency stabilized electrics


Beat Frequency measurements ASTROD Symposium 2006, July 14-16, Beijing

Allan Standard Deviation of Each Laser (10-15 )

Averaging time

Continuous measurement time （ s）15104 5104 2104 1104 6103

1s 24.11 23.44 22.01 21.57 20.57

10s 8.331 7.705 7.237 7.328 6.906

100s 4.509 4.862 3.987 4.414 3.950

1000s 3.860 3.454 3.374 3.625 2.541

2000s 3.886 3.141 3.596 1.240

5000s 4.025 1.967

10000s 3.864


Frequency Shift Measurements

0 1 2 3 4 5 6-2500

-2000

-1500

-1000

-500

0

Fre

qu

en

cy s

hift

(H

z)

Pump power (mW)

532nm GY1, gate time 1sMeasuring time for each power is 200s

0 2 4 6 8 10-200

-150

-100

-50

0

50

100

Fre

quen

cy s

hift

(Hz)

Pump power (mW)

532nm NY1, gate time 1sMeasuring time for each power is 200s

Pressure frequency shift

Power frequency shift


Theoretical and Current Observed Linewidths of Trapped Ion Clock Transitions

Ion Clock (nm) Theoretical Current Lowestune.(1)

(Hz) transitiuon linewidth(Hz) linewidth(Hz) of fre. meas.(Hz)

199Hg + 2S 1/2-2D 5/2 282 1.7 6.7 10

171Yb + 2S 1/2-2D 3/2 435 3.1 30 6

88Sr + 2S 1/2-2D 3/2 674 0.4 70 100

115In + 1S 0-3P 0 236 0.8 170 230

171Yb + 2S 1/2-2F 7/2 467 ~10-9 180 230

40Ca + 2S 1/2- 2D5/2 729 0.2 1000

• Frequency value of 40Ca + was not recommended by CIPM as reference for the

• Realization of the meter

Contributions to the standard uncertainty of the 40Ca optical frequency

standard determined at T=3 mK and envisaged for T=6 K

Effect T=3mK(Hz) T=6K (mHz)Residdual fist-order Doppler effect 2.6 150Second-order Doppler effect 0.005 0.025 Asymmetry of line shape 0.05 50Other phase Contributions 4 100Magnetic field(60Hz mT-2) 0.1 80Quadratic Stark effect 0.06 20(|E|<2V cm -1) Blackbody radiation 4.3 50Servo electronics 3.2 100Influence of cold atom coll 1.8 260Statistical uncertainty of 3 <5frequency comparison Total uncertainty 8 350Total relative uncertainty / 2 10 –14 8 10 -16


The optical part of Sr atom apparatus ， six Brewster’s windows are

input sides of lasers ， cool trapped Sr atoms are in the center part

Developing Definition of Second and Frequency Standards

Cold atom microwave frequency standards: Cs,Rb Optical cold atom frequency standards : Ca, Mg, Sr Ion frequency standards : ： 199Hg +,115In + ,88Sr + , 87Sr + , 171Yb + ,Ca +

CIPM – CCTF adopted a 2001resolution to seek secondary ‘representations’ of the second. Such representations can be based on

the different cold ion and atom standards ,both optical and microwave, and would be able to take full advantage of improved stability and reproducibility, but remain limited to the caesium accuracy. This position represents a useful intermediate stage for evaluating the systematics of different systems prior to making any rational choice for a new time definition.

Method of synchronization between satellite clock B and earth reference clock A:

1. Define the characteristic parameter of relative motion : assume that A sends two signals to B which are spaced tA seconds ap

art according to clock A. Due to the relative motion of A and B, the two signals will arrive at B with a different time spaci

ng as measured by B. The parameter is simply the ratio of the latter time spacing to the former, i.e., the two signals arrive with time spacing tA according to clock B. Because th

e relative motion is uniform, does not depend on tA . If there is no relative motion between A and B, = 1.

2. If B sends two signals to A which are spaced tB seconds apart accor

ding to clock B. According relativity principle, the two signals will arrive at A with time spacing tB as measured by A. From the definiti

on of given above, we see that = (t2B – t1B )/(t2A – t1A ) = (t3A – t2A )/(t2B – t1B )

=[(t3A – t2A )/(t2A – t1A )]1/2


Without Locking Locking

Method of Synchronization

If B were synchronized to A, the time reading t1B and t2B would becomes1B and s2B . This is accomplished by determining s1B , which determines the correction s1B - t1B that needs to be applied, defined as B . One determines s1B by assuming the clocks were synchronized , so that each would indicate the same time t0 at the fictional moment of spatial coincidence. Imaging that A sends a radio signal at that very moment. The signal is simultaneously received at time t0 according to synchronized clock B. We have = (s1B – t0 )/(t1A – t0 ) = (t2A – t0 )/(s1B – t0 ) , 2 = (t2A – t0 )/(t1A – t0 ) Then, t0 = (2t1A – t2A )/(2 –1) , s1B= (t2A + t1A )/(+1). Define the starred distance d1AB from A to B at the instant s1B of reception of the signal sent by A at time t1A , as follow: d1AB = c (s1B – t1A ), where c is the speed of light as it travels from A to B. Then d1AB = c (t2A – t1A )/(+1). Now define the starred radial velocity vrAB between A and B as follow: vrAB =d1AB/s1B = [c (t2A –t1A )/(+1)]/[(t2A + t1A )/(+1)] =c (t2A–t1A)/(t2A+t1A) = c (-1)/.


1. Define the characteristic parameter of relative

motion :

assume that A sends two signals to B which are spaced tA seconds apart according to clock A. Due to the relative motion of A and B, the two signals will arrive at B with a different time spacing as me

asured by B. The parameter is simply the ratio of the latter time spacing to the former, i.e., the two signals arrive with time spacing tA according to clock B. Because the relative motion is uniform,

does not depend on tA . If there is no relative motion between A and B, = 1.

2 If B sends two signals to A which are spaced tB

seconds apart according to clock B. According relativity principle, the two signals will arrive at A with time spacing tB as measured by A. From t

he definition of given above, we see that = (t2B – t1B )/(t2A – t1A )

= (t3A – t2A )/(t2A – t1A )

=[(t3A – t2A )/(t2A – t1A )]1/2


Method of synchronization between satellite clock B and earth

reference clock A:


Method of Synchronization

If B were synchronized to A, the time reading t1B and t1B would become s1B and s2B . This is accomplished by determining s1B , which determines the correction s1B - t1B that needs to be applied, defined as B .

One determines s1B by assuming the clocks were synchronized, so that each would indicate the same timet0 at the fictional moment of spatial coincidence. Imaging that A sends a radio signal at that very moment. The signal is simultaneously received at time t0 according to synchronized clock B. We have

= (s1B – t0 )/(t1A – t0 ) = (t2A – t0 )/(s1B – t0 ) ,

2 = (t2A – t0 )/(t1A – t0 )

Then, t 0 = (2t1A – t2A )/(2 –1) ,

s1B= (t2A + t1A )/(+1).

Define the starred distance d 1AB from A to B at the instant s1B of

reception of the signal sent by A at time t1A , as follow:

d 1AB = c (s1B – t1A ),

where c is the speed of light as it travels from A to B. Then d 1AB = c (t2A – t1A )/(+1).

Now define the starred radial velocity v rAB between A and B as follow:

v rAB =d 1AB/s 1B = [c (t2A –t1A )/(+1)]/[(t2A + t1A )/(+1)]

= c (t2A–t1A)/(t2A+t1A) = c (-1)/.

The End

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The Development of Optical Frequency Standards and its Application to Space Missions Naicheng Shen...

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