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| | Internal colloquium
A conceptual introduction to laser frequency stabilization
Jesse Zhang
Internal Colloquium, 22nd November 2019
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| | Internal colloquium 22.11.19 Laboratory for Positron and Positronium Physics 2
Pound-Drever-Hall locking A conceptual introduction to laser - - PowerPoint PPT Presentation
Pound-Drever-Hall locking A conceptual introduction to laser - - PowerPoint PPT Presentation
Pound-Drever-Hall locking A conceptual introduction to laser frequency stabilization Jesse Zhang Internal Colloquium, 22 nd November 2019 | | Internal colloquium 1 Interests in laser stabilization f L Laboratory for Positron and
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| | Internal colloquium 22.11.19 Laboratory for Positron and Positronium Physics 3
Relating laser frequency to cavity length
Laser Cavity Servo Error signal Electronic feedback PZT PD
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| | Internal colloquium 21.11.19 Laboratory for Positron and Positronium Physics 4
Transmission and Reflection through cavity
Eric D. Black. An introduction to Pound-Drever-Hall laser frequency stabilization.
- Am. J. Phys., 69, 2000.
!"# = %/2(
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| | Internal colloquium
▪ Hold reflection at zero ▪ Problem: symmetric signal ▪ decrease or increase frequency? ▪ Derivative is antisymmetric
▪ Vary frequency and see the response on the reflected beam
22.11.19 Laboratory for Positron and Positronium Physics 5
Using the reflection signal
Frequency [a.u.] Reflected intensity [a.u.]
Compare variation of reflected intensity and frequency variation and feed this measurement back to laser/cavity.
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| | Internal colloquium
▪ Modulate laser frequency driven by oscillator ▪ Pick of reflected light with photodetector ▪ Mix PD signal with oscillation signal ▪ -> PDH error signal
21.11.19 Laboratory for Positron and Positronium Physics 6
The PDH error signal
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| | Internal colloquium 21.11.19 Laboratory for Positron and Positronium Physics 7
The PDH setup
Eric D. Black. An introduction to Pound-Drever-Hall laser frequency stabilization.
- Am. J. Phys., 69, 2000.
EOM
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| | Internal colloquium 21.11.19 Laboratory for Positron and Positronium Physics 8
Real world problems
Theory Reality
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| | Internal colloquium 21.11.19 Laboratory for Positron and Positronium Physics 9
99 problems but error signal ain’t one
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| | Internal colloquium 21.11.19 Laboratory for Positron and Positronium Physics 10
Our PDH setup
EOM PD for reflected light
Servo electronics
PZT
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| | Internal colloquium
▪ Pockels effect: ▪Refractive index changes proportional to electric field strength ▪-> need high voltage ▪ Modulation of 5 MHz
▪ Can pass through cavity for further use downstream
Electro-optic modulator (EOM)
Laboratory for Positron and Positronium Physics 22.11.19 11
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Thank you for your attention!
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| | Internal colloquium 21.11.19 Laboratory for Positron and Positronium Physics 13
Backup: Constructive interference
Laser Cavity
Frequency f Cavity length L 2L = n & ⟺
( = ) * +,
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| | Internal colloquium
§ Modulate phase rather then frequency
§!"# = !%&'()*+ , -"# .*) ≈ !% 1% 2 &3)* + 15 2 &' )+. * − 15 2 &' )3. *
§ Creates two FM sidebands § Reflected light yields to beats at modulation frequency Ω § On resonance beats are 180° out of phase
21.11.19 Laboratory for Positron and Positronium Physics 14
Back up: Modulating the beam: side bands
Frequency [a.u.] Reflected intensity [a.u.] 8 8 - Ω 8 + Ω