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ABSTRACT. We present a method of frequency stabilizing a broadband etalon that can serve as a high-precision wavelength calibrator for an echelle spectrograph. Using a laser to probe the Doppler-free saturated absorption of the rubidium D 2 line, we stabilize one etalon transmission peak directly to the rubidium frequency. The rubidium transition is an established frequency standard and has been used to lock lasers to fractional stabilities of <10 À12 , a level of accuracy far exceeding the demands of radial velocity (RV) searches for exoplanets. The stabilized bandwidth depends on the dispersion characteristics of the etalon. We describe a simple setup designed specifically for use at an observatory and demonstrate that we can stabilize the etalon peak to a relative precision of <10 À10 ; this is equivalent to 3 cm s À1 RV precision.

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We report on a universal method to achieve and sustain a large mode-hop-free tuning range of an external cavity diode laser based on a model of its mode-structure dynamics. Using this method, we were able to scan 73 GHz mode-hop free by using an uncoated off-the-shelf laser diode with a central wavelength of 785 nm. Our model applies to any laser system requiring synchronization of more than one optical element.

We report on an universal method to achieve and sustain a large mode-hop free tuning range of an external cavity diode laser. By locking one of the resonators using a closed loop control based on polarization spectroscopy while tuning the laser we achieved mode-hop free tuning of up to 130 GHz with a non AR-coated, off-the-shelf laser diode.