From Chains to Short Pulses: Absolute Frequency Measurements Across - - PowerPoint PPT Presentation

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From Chains to Short Pulses: Absolute Frequency Measurements Across - - PowerPoint PPT Presentation

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From Chains to Short Pulses: Absolute Frequency Measurements Across the Optical Spectrum A.A. Madej , J.E Bernard, A. Czajkowski, L. Marmet, P. Dub, and K.J. Siemsen Work Partially March 13, 2003 Supported by : International Comb Workshop

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SLIDE 1

From Chains to Short Pulses: Absolute Frequency Measurements Across the Optical Spectrum

A.A. Madej, J.E Bernard, A. Czajkowski, L. Marmet, P. Dubé, and K.J. Siemsen

March 13, 2003 International Comb Workshop BIPM, Sèvres, France

Work Partially Supported by : Canadian Institute for Photonic Innovations (CIPI)

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SLIDE 2

Counting Optical Frequencies

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SLIDE 3

Measurement of Optical Frequencies via Chains Measurement of Optical Frequencies via Chains

*Frequency Chain Philosophy:

  • By non-linear stages link laser oscillators at different portions of the

electromagnetic spectrum.

  • Cascade these intermediate oscillator stages to higher absolute frequencies until
  • ne reaches the frequency to be measured.
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SLIDE 4

NRC Frequency Chain to the Visible

A frequency chain was devised to span the factor

  • f 50,000 ratio in

frequency between the visible light probing the ion and the Cs reference standard at 9.1 GHz. The chain consisted of 5 CO2 lasers, 2 solid state lasers, 2 microwave oscillators and 8 phase locked servo loop systems.

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SLIDE 5

NRC Single Strontium Ion Trap

Artist Impression of Trap and Excitation Beams

View of Chamber and Photomultiplier

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SLIDE 6
  • Single Sr+ Ion held in 1-mm Paul Trap and cooled to 5 -10 mK.
  • Probing on S-D quadrupole transition (0.4 Hz) using ULE cavity

stabilized diode laser. Single, Laser Cooled Sr+ Optical Frequency Standard

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SLIDE 7
  • Cs based frequency chain

measurements on four different experimental days spanning over a year have yielded a hundred fold improvement on the previous value

  • f the ion frequency.
  • Based on these results, the centre

frequency of the ion transition is determined to be : 444 779 044 095. 4 ± 0.2 kHz (1 ) Single, Laser Cooled Sr+ Optical Frequency Standard

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SLIDE 8

Extending Ion Accuracy across the Spectrum

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SLIDE 9

Using the Sr+ Standard to Measure the Frequency of the HeNe/I2 Standard at 474 THz (633 nm)

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SLIDE 10

Determination of 474 THz Standard Frequency

On three different experimental days, determinations of the NRC INMS 3 standard frequency stabilized to component "f" gave 473 612 353 595 ± 1 kHz. The CIPM recommended value for this transition is: 473 612 353 597 ± 12 kHz. From April 10 -14, 2000 intercomparisons were performed with lasers from the BIPM and JILA/NIST.

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SLIDE 11

A Miracle of Nature:Femtosecond Lasers as Frequency Combs

  • In the Time Picture, the

mode-locked laser consists of a series of pulses of length t separated by a pulse repetition of = 1/ frep.

  • In Frequency, this

creates a comb of individual frequencies separated by = 1/ and where the spread is inversely related to the pulse duration.

For Femtosecond lasers, the effective bandwidth can be extremely large. (t = 10 fs, = 160 THz) Locking the pulse repetition rate frep stabilizes the comb to high accuracy.

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SLIDE 12

Extending the spectrum of the comb elements

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SLIDE 13

Measuring the Absolute Frequency of Each Comb Element Measuring the Absolute Frequency of Each Comb Element

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SLIDE 14

NRC Femtosecond Comb for Measurement of Optical Frequencies

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SLIDE 15

Characteristics of NRC Frequency Comb

Comb Spectrum

0.2 0.4 0.6 0.8 1 400 500 600 700 800 900 1000 1100 1200 Wavelength (nm) Pow er (arbritary units)

Fibre length = 25 cm Total power = 170 mW

May1602_Spec1.xls

Over an octave spectral coverage has been

  • btained with the NRC

frequency comb extending from 510 nm to beyond 1060nm. The generated broad spectrum is coherent yet possesses structure that depends of the input launch polarization, intensity and coupling into the microstructure fibre.

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SLIDE 16

Stabilizing the Frequency Movement of the Comb Ensemble

fo Beat with the Comb locked

  • 90
  • 80
  • 70
  • 60
  • 50
  • 40
  • 30
  • 20
  • 10

290 291 292 293 294 295 296 297 298 299 300

Frequency (MHz) Power (dBm)

Resolution bandwidth = 100 kHz

*By comparing the second harmonic of the lower frequency end of the comb with the upper end located at same frequency, a heterodyne beat is

  • btained which is

equal to the offset

  • f the comb as a

whole when extrapolated to zero

  • frequency. Phase

locked stabilization

  • f the beat is

utilized.

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SLIDE 17

Measurement of I Measurement of I2

2/HeNe Standard using Comb

/HeNe Standard using Comb

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SLIDE 18

Recent Results from NRC Comb : 474 THz I2/HeNe Standard

Elapsed Time [s]

100 200 300 400 500 600

Absolute Frequency [ f -473 612 353 595 000 + X] [Hz]

  • 15000
  • 10000
  • 5000

5000 10000 15000 Averaging Time [s]

1 10 100

Allan Deviation [Hz]

100 1000 10000

*Full Phase-Locked

  • peration of the

repetition rate and comb position for the NRC Frequency comb was

  • achieved. The system

was used to measure the INMS 3 Iodine stabilized HeNe Laser at 474 THz.

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SLIDE 19

Recent Results from NRC Comb : 474 THz I2/HeNe Standard (cont.)

  • Comparing the Comb based

measurements with results

  • btained in April,2000 leads

to a remarkable agreement between methods at the 200Hz level.

  • The April 2000 work used

the single Sr+ ion standard as a reference and connected the 474 THz light by a 28 THz CO2 laser measured by the old NRC frequency Chain through non-linear mixing methods.

Observed Absolute Frequency of NRC INMS 3 Laser on Component "f"

Run Identifier 2 4 6 8

Absolute Laser Frequency [ 473 612 353 595 000 +X] [Hz]

200 400 600 800 1000 1200 1400 April 12, 2000 Ion Based Chain May 21, 2002 Comb Measurements

Observed Absolute Frequency of NRC INMS 3 Laser on Component "f"

Run Identifier 2 4 6 8

Absolute Laser Frequency [ 473 612 353 595 000 +X] [Hz]

200 400 600 800 1000 1200 1400 April 12, 2000 Ion Based Chain May 21, 2002 Comb Measurements

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SLIDE 20

Measurement of Single Ion Standard using Comb Measurement of Single Ion Standard using Comb

Time of Day [s] 76400 76600 76800 77000 77200 77400

S-D Frequency [ 444 779 044 095 400 ] [Hz]

  • 1500
  • 1000
  • 500

500 1000 1500 2000

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SLIDE 21

Recent Results from NRC Comb : 445 THz Single Ion Frequency

  • Absolute measurements
  • f the 88Sr+ 5s 2S1/2- 4d

2D5/2 transition were

performed with the Comb applied to the NRC Single Ion Standard.

  • The preliminary total

result of the 4 days of study spanning a period of 4 months yielded an uncertainty of ±50 Hz whose value agrees with the NRC Chain measurement and recent comb measurements by the NPL group.

5 10 15 20 25 30

S-D Frequency [ f - 444 779 044 095 000] [Hz]

  • 1000
  • 500

500 1000 1500 2000

fSD= 444 779 044 095 494 ± 50 Hz

  • 2
  • 1

1 2 3 4 5

S-D Frequency [ f - 444 779 044 095 400] [Hz]

  • 300
  • 200
  • 100

100 200 300

fSD= 444 779 044 095 494 ± 50 Hz

NRC Chain (1999) NPL Comb (2002) NRC Comb (2002)

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SLIDE 22

Summary Comparison of Chain and Comb Technologies Summary Comparison of Chain and Comb Technologies

Chain Technology

  • Laser Technology necessary

across the spectrum

  • Many Phase Locked Loops

(PLL) necessary to reach up to visible region (phase noise multiplication, Complex)

  • Built to measure one specific

frequency region.

  • Need power from laser to be

measured ( > 100 µW- 1mW).

  • Multi-year projects that existed

in a few laboratories.

Comb Technology

  • One Modelocked Femtosecond

laser (Ti:Sapphire or ...)

  • 1-2 PLLs only necessary to

stabilize comb spacing and possibly comb offset (phase noise much lower, Simpler)

  • Can in principle measure

frequencies across one spectral

  • ctave.
  • Need power from laser to be

measured (> 100 µW).

  • Widely available technology with

short startup times and flexibility.

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SLIDE 23

Applications of Optical Combs