Michael Matus Bundesamt für Eich und Vermessungswesen, · 2013. 10. 15. · Michael Matus...
Transcript of Michael Matus Bundesamt für Eich und Vermessungswesen, · 2013. 10. 15. · Michael Matus...
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CCL Workshop on comb technology, March 2003
Bundesamt für E ich- und Vermessungswesen
Experiences with a commercial comb generator at the BEV
Michael MatusBundesamt für E ich und Vermessungswesen,Arltgasse 35, A-1160 Wien, Austriam.matus@ metrologie.at
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Outline
1. Motivations for ins talling a comb generator atthe BEV
Primary standard for length metrology. T ype of instrument chosen
2. S pecial problems (and solutions) in lengthmetrology
low-power and frequency modulated lasers (mise en pratique)
3. Laser-frequency measurements as a s tandardservice to the public?
current s tatus and outlook
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Motivation
T raditional laser intercomparisons campaigns:• mostly limited to 633 nm (2 I2-s tabilized lasers as primary
standards at the BEV)• rather time consuming
• will come to an end in the near future anyway
Optical femtosecond comb generator:• direct realisation of the definition of the meter
• wavelength range extended• no need for specialized laser sources; working standards can be
calibrated directly (gauge block interferometer)• service for the “public”, i.e for other NMI´s
• other goodies (e.g. Cs-controlled ECDL)
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S etup
magic magic fiberfiber
NL -NL -interferometerinterferometer
pump-laserpump-laser
AOMAOM
T iT i:S -L aser:S -L aser
experimentexperiment
ins talled: Jan. 2002price: ~ 300 k
S er.Nr.: 001
Offspring company of MPQ
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S pecial problems in length metrology (1)
ProblemsFeatures of some CCL lasers :• Low output power• S trong frequency modulation
Features of the comb:• Low output power per comb
mode (~10 nW)• High background (~1000 comb
modes reach the APD togetherwith the laser)
• S pectral “holes” in the fibrestretched light (near 633 nm)
• Wavefront dis tortion due to NL-interferometer for l > 600 nm
S olutionsF irs t s teps for 633nm• Powerful backup lasers• T esting of different fibres (trial
and error)
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HeNe - 633 nm via 2-mode laser
Due to experimentalboundary conditions
only component “c” canbe measured without
us ing an additionalmixer and local
oscillator.
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HeNe - 633 nm via ECDL
T he frequency of the ECDL is locked to a particular comb modeand can be tuned over some nm (“amplified comb mode”).
In practice it is difficult for a s ingle operator to lock the ECDL to themode des ired. Also the high output power is partially wasted
because of the rather poor beam geometry.
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S pecial problems in length metrology (2)
ProblemsFeatures of some CCL lasers :• Low output power• S trong frequency modulation
Features of the comb:• Low output power per comb
mode (~10 nW)• High background (~1000 comb
modes reach the APD togetherwith the laser)
• S pectral “holes” in the fibrestretched light (near 633 nm)
• Wavefront dis tortion due to NL-interferometer
S olutionsF irs t s teps for 633nm• Powerful backup lasers• T esting of different fibres (trial
and error)
Current system (minor modificationsto original system)
• Optical separation of spectralregion of interest from the NL-interferometer
• Mode matching of combradiation and laser beam
• T echnique for checking thevalidity of the beat frequencyreadings
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Present setup
Laser to becalibrated
ReplacedmirrorDichroic mirror, hightransmittance at 45°from 600 - 900 nm
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Minimal laser power
Laser power atAPD even lowerby approx. 40 %
S ens itivity sufficient for most lasers !
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F ilter band width
Narrow band RF-filter not necessary!
Us ing narrow bandfilters together with
frequency modulateds ignals can cause big
errors .
Passband ~25 MHz
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Cycle s lip detection
S imple method toensure validity of
beat-frequencyreadings
drawback:laser power must be
s lightly higher
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Results obtained during EUROMET #647
532 nm CMI YAG1 [32-0 R(56) a10] (~500 µW)563 260 223 514.3 kHz ± 0.4 kHz
543 nm PLG1 [28-0 R(106) b10] (~15 µW)551 580 162 396.6 kHz ± 0.6 kHz
633 nm BEV2 [11-5 R(127) f ] (~90 µW)473 612 353 604.36 kHz ± 0.14 kHz
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F requency s tability
T wo samples variance as measured with the comb for sample times>10 s as good as one can expect from the standard!
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Present s tatus
• Instrument is working fine and reliable. Eventhe fibre survived all experiments so far.
• Calibrations on 543nm and 633nm lasers arenow performed as a regular service.
• Already applied for entry in the cmc tables(520 nm – 1150 nm, U rel=10-9)
• Comb generator now included (as the nationals tandard) in the hierarchy scheme for lengthmeasurements .
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hierarchy scheme for dimens ional measurements
Overview of traceability for dimens ionalcalibrations (and verifications) covered by
BEV‘s quality sys tem.
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T op-level services
T he optical femtosecondcomb generator is now the
primary (national)s tandard for all length
measurements traceableto the BEV.
T he I2-s tabilized lasers BEV1and BEV2 can still be
used as primary s tandardsbut it makes more sense
to employ them as transferand travelling s tandards
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Conclus ion
• For ins titutes with the need for more than as ingle wavelength, the femtosecond combgenerator as a length s tandard is an option!(as opposed to build and maintain a variety ofCCL lasers).
• Calibration of secondary s tandards (2-modestabilized etc.) is now not more elaborate thanthe traditional way. For this lasers even thebeat frequency measurement us ing aspectrum analyser might be adequate.
• We are confident in the reliability of thistechnique to offer it as a service to the public.