Study of the frequency fluctuations of a semiconductor diode laser

Ayan Ray

Research output: Contribution to journalArticlepeer-review

7 Scopus citations


Frequency fluctuations of an inexpensive single-mode semiconductor diode laser, which operates in the 822 nm region, are investigated by direct measurement of the error signal. The linear slope of first derivative signal of a transition in the (2,1,1) vibration-rotation band of water vapour is used as a frequency discriminator. A balanced photodetector is used to reduce the intensity noise and to improve the S/N ratio. Frequency stability of the diode laser is investigated when the laser is under a free-running condition and is locked to the line center of the reference transition. An integrator is used to provide feedback voltage to the laser current driver. After frequency stabilization, a more than 60-fold improvement in long-term laser-frequency stability is attained over the performance provided by the free-running semiconductor diode laser. The frequency-noise power spectrum of the diode laser is extracted from the error signal for the Fourier-frequency range ∼100 Hz. The Allan variance curve for the laser system is obtained from the frequency-noise power spectrum of the error signal by using a suitable mathematical relation under certain approximations. The extracted, values of the Allan variance are compared with the theoretical τ-1 model. The experimental setup is easy to implement in graduate laboratory classes.

Original languageEnglish
Pages (from-to)351-358
Number of pages8
JournalCanadian Journal of Physics
Issue number2
StatePublished - Feb 2008
Externally publishedYes


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