Piezo-locking a diode laser with saturated absorption spectroscopy

Applied Optics

Volumn 47, Issue 28, 2008, Pages 5163-5166

  Debs, J E ^a   Robins, N P ^a   Lance, A ^a   Kruger, M B ^b   Close, J D ^a  

^a AUSTRALIAN NATIONAL UNIVERSITY   (Australia)

^b UNIVERSITY OF MISSOURI KANSAS CITY   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

ABSORPTION SPECTROSCOPY; ATOMIC PHYSICS; BOSE-EINSTEIN CONDENSATION; LASER RESONATORS; LOCKS (FASTENERS); MODULATION; SEMICONDUCTOR LASERS; STATISTICAL MECHANICS;

BOSE-EINSTEIN CONDENSATES; ERROR SIGNAL; EXTERNAL-CAVITY DIODE LASER; FREQUENCY LOCKING; HYPERFINE TRANSITION; SATURATED-ABSORPTION SPECTROSCOPY;

LASER MIRRORS;

EID: 60749100102     PISSN: 1559128X     EISSN: 15394522     Source Type: Journal    
DOI: 10.1364/AO.47.005163     Document Type: Article

References (22)

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3. We find that even for small modulation depth, the linewidth of an inherently narrow ECDL is broadened by using this technique.
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17. This estimate is calculated based on a typical saturated absorption signal with 300//W of power focused onto the photodetector. We assume a Lorenzian absorption profile and use Beer's law with Eq. () to calculate a theoretical error signal for a modulation frequency of 100 kHz. The absolute lower limit of 1 Å is based on a feedback bandwidth of 200 Hz, a value that is typical for two of our three BEC lasers, whereas a value of 10 A is the lower limit required for a feedback bandwidth of 20 kHz. Both of these values result in a signal-tonoise ratio of approximately 5 relative to the shot noise, leading to theoretical stability in the lock point of 200 kHz in the laser output frequency.
18. Diode laser purchased from TOPTICA Photonics AG, Model DL 100; see http://www.toptica.com/page/scientific-lasers. php.
19. This value is based on a 50 mm focal length for the lens in Fig. and a tilt angle of 50 μrad, calculated assuming a 200 nm arclength due to the tilt. We feel this estimate of arclength is a more than generous number, given the previously measured piezo displacements referenced in the paper.
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22. The self-heterodyne beat measurement uses an AOM to scatter a portion of the laser beam into the first order, producing a frequency-shifted beam (̃200 MHz for our AOM). The unscattered zeroth order is then launched into a single-mode optical fiber before being mixed with the first order on a beam splitter. The length of the fiber should be significantly longer than the coherence length of the laser, rendering the zeroth-order beam incoherent relative to the first order. Upon mixing the two beams, a beat signal is obtained at the AOM drive frequency, and as long as the two beams are sufficiently incoherent, this results in a reliable measurement of the laser linewidth without the need for locking two identical lasers. Note that a laser with a 100 kHz linewidth has a coherence length of about 2 km, which is significantly shorter than the 3 km of fiber used in our setup.