Preliminary Experimental Results From the Femtosecond Frequency Comb

							Frequency Comb and Length
        Metrology



                 Z. Fang
Quantum Division, NIM, Beijing, 2004-10-18
Outline
 Introduction
 Principle
 NIM’s comb system
   Femtosecond laser
   Supercontinuum generation using PCF
   Repetition rate fr
   Carrier envelop offset frequency fCEO
 Application
 New developments
Outline
 Introduction
 Principle
 NIM’s comb system
   Femtosecond laser
   Supercontinuum generation using PCF
   Carrier envelop offset frequency fCEO
   Repetition rate fr
 Application
 new developments
The Meter is the length of the path traveled by light in
vacuum during a time interval of 1/299 792 458 of a
second.
                                   –1983, 17th CGPM
         Recommended radiations for the realization of
              the definition of the meter (2001)
I2 R(127) He-Ne (633 nm)                    473 612 353 604 (10) kHz         2.1×10-11

I2 R(56) Nd:YAG (532nm)                     563 260 223 514 (5) kHz          8.9×10-12

OsO4 (CO2) (10.3µm)                         29 054 057 446 579(4) Hz         1.4×10-13

CH4 P(7) (3.39µm)                           88 376 181 600.18(0.27) kHz      3.0×10-12
85Rb    5S1/2-5D5/2 (778nm)                 385 285 142 375(5) kHz           1.3×10-11
13C H P(16)    (1542nm)                     194 369 569.4 (0.1) MHz          5.1×10-10
   2 2

1H   1S-2S (243nm)                          1233 030 706 593.60(0.025) kHz 2.0×10-14
40Ca 1S -3P (657nm)                         455 986 240 494 150(50) Hz       1.1×10-13
       0   1

88Sr+   52S1/2-42D5/2 (674nm)               444 779 044 095.5(0.35) kHz      7.9×10-13
199Hg+5d106s2S1/2(F=0)-5d96s22D5/2(F=2)     1 064 721 609 899 143(20) Hz     1.9×10-14
(281nm))
171Yb+ 2S -2D (F=2)       (435nm)           688 358 979 309 312(12) Hz       1.7×10-14
         1/2 3/2

171Yb+ 2S (F=0,
         1/2       mF=0)-2F7/2(F=3, mF=0)   642 121 496 772.6(2.6) kHz       4.0×10-12
(467nm)
115In+ 5s21S -5s5p3P (236.5nm)              1 267 402 452 899.92(0.46) kHz   3.6×10-13
            0       0
                                 Speed of light
                       c
                    λ=
       wavelength      f           frequency


The speed of light in vacuum is exactly 299,792,458
m/s (metres per second).

The second is the duration of 9 192 631 770 periods of
the radiation corresponding to the transition between the
two hyperfine levels of the ground state of the caesium
133 atom.
  µWave              Optical                Optical
Frequency           Frequency             Frequency
 Standard             Chain                Standard

  ~109Hz                                   ~1014Hz

            • harmonic frequency chain
            •femtosecond frequency comb
Comparing with harmonic frequency
chains, fs frequency combs are:
− Cost effective
− Compact
− Easy in operation and maintenance
− Reliable
− Measure any optical frequency from IR to
  Visible
− …
Outline
 Introduction
 Principle
 NIM’s comb system
   Femtosecond laser
   Supercontinuum generation using PCF
   Carrier envelop offset frequency fCEO
   Repetition rate fr
 Application
 New developments
                                                                Supercontinuum
                                                          0




                               Spectral Intensity (dB)
                                                         -10



                                                         -20
Ti:sapphire
   Laser
                                                         -30
              Microstructure
                   Fiber                                 -40
                                                               600   800   1000   1200   1400
                                                                Wavelength (nm)
                                  fr

I(f)   fo




                                                          f
0
            fn = n fr + fo   x2         f2n = 2nfr + fo

                                       fo
            fun = nfr + fo+ fb
                                  fun                         RF Beat fb
     I(f)                                        repetition
              fo = fr ∆φ/2π                    frequency fr



                                                              f
     0                                  fn = nfr + fo


                        Locking
                       Electronics

                                             Stability and
Cesium Time             Hydrogen             accuracy of RF
 Standard                 Maser              standard passed to
  ~9 GHz                 10 MHz              optical frequencies
Outline
 Introduction
 Principle
 NIM’s comb system
   Femtosecond laser
   Supercontinuum generation using PCF
   Carrier envelop offset frequency fCEO
   Repetition rate fr
 Application
 New Developments
Outline
 Introduction
 Principle
 NIM’s comb system
   Femtosecond laser
   Supercontinuum generation using PCF
   Carrier envelop offset frequency fCEO
   Repetition rate fr
 Application
 New developments
Outline
 Introduction
 Principle
 NIM’s comb system
   Femtosecond laser
   Supercontinuum generation using PCF
   Carrier envelop offset frequency fCEO
   Repetition rate fr
 Application
 New developments
PCF structure   PCF dispersion profile
Bath PCF, ~160cm length, 2.0µm core size
PCF structure                    PCF dispersion profile
                Crystal Fiber A/S PCF
Danish PCF, ~60cm length, 2.0µm core size
Things Affect SC Generation…

  Mode-locked Ti:S laser: pulse width,
  power level, polarization, central
  wavelength…

  PCF side: core size, length, zero-dispersion
  wavelength, design structure,…

   State of Ti:S laser is the most important!
Outline
 Introduction
 Principle
 NIM’s comb system
   Femtosecond laser
   Supercontinuum generation using PCF
   Carrier envelop offset frequency fCEO
   Repetition rate fr
 Application
 New Developments
Things Affect fceo S/N…
  SC performance: power level, structure,…State of
  Ti:s laser is the most important!
  High efficient SHG, KTP
  Spectral and spatial overlap
  Temporal overlap
  Dispersion prism and diaphragm is necessary
  Fiber tip glued
  Finally, a stable coupling stage is essential!
Based on following experiments, we believe the
performance of our comb is better than 1.6×10-12.
Outline
 Introduction
 Principle
 NIM’s comb system
   Femtosecond laser
   Supercontinuum generation using PCF
   Carrier envelop offset frequency fCEO
   Repetition rate fr
 Application
 New Developments
Outline
 Introduction
 Principle
 NIM’s comb system
   Femtosecond laser
   Supercontinuum generation using PCF
   Carrier envelop offset frequency fCEO
   Repetition rate fr
 Application
 New Developments
Institute    Atom/ion nm       λ(um)        Frequency               Relative uncertainty   Time

MPQ         Hydrogen (1S-2S)   121     2466061413187103(46) Hz           1.9E-14           2000

MPQ         Caesium D1         895     335 116 048 807(41) kHz           1.2E-10           1999

MPQ         Indium ion         236     1267 402 452 899.92(0.23) kHz 1.8E-13               2000

JILA        Rubidium           778     385 285 142 374.8(3.0) kHz        7.8E-12           2000

JILA        Iodine/YAG         532     563 260 233 514(5) kHz            8.9E-12           2000

JILA        Iodine/HeNe        633     473 612 214 711.9(2.0) kHz        4.4E-12           2001

NIST        Mercury ion        282     1064 721 609 899 143(10) kHz      9.4E-15           2001

NIST        Calcium            658     455 986 240 494 158(26) Hz        5.7E-14           2001

PTB         Calcium            658     455 986 240 494 250(180) Hz       4.0E-13           2001

PTB         Ytterbium ion      435.5   688 358 979 309 312(6) Hz         1.0E-14           2001

LPTF        Iodine/YAG         532     563 260 223 511 857(88) Hz         1.6E-13          2002

NPL         Iodine/HeNe        532     473 612 353 612.9(0.7) kHz         1.5E-12          2003
“Optical Frequency Synthesis and Comparison with Uncertainty at the 10-19 Level”.
-Adapted from L.-S. Ma, SCIENCE VOL 303 19 MARCH 2004
“Absolute measurement of a long,
arbitrary distance to less than an optical
fringe”. –Adapted from Jun Ye, Optics
Letters, Vol.29 No.10 (2004)
  µWave       optical     Optical
Frequency   Frequency   Frequency
 Standard     comb       Standard

  ~109Hz                 ~1014Hz
Outline
 Introduction
 Principle
 NIM’s comb system
   Femtosecond laser
   Supercontinuum generation using PCF
   Carrier envelop offset frequency fCEO
   Repetition rate fr
 Application
 New Developments
Fiber Optical Frequency Comb @ 1.5µm
Thank you!