Article

# A 12.5 GHz-Spaced Optical Frequency Comb Spanning > 400 nm for Astronomical Spectrograph Calibration

National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80305, USA.
(Impact Factor: 1.61). 06/2010; 81(6):063105. DOI: 10.1063/1.3436638
Source: PubMed

ABSTRACT

A 12.5 GHz-spaced optical frequency comb locked to a global positioning system disciplined oscillator for near-infrared (IR) spectrograph calibration is presented. The comb is generated via filtering a 250 MHz-spaced comb. Subsequent nonlinear broadening of the 12.5 GHz comb extends the wavelength range to cover 1380-1820 nm, providing complete coverage over the H-band transmission window of earth's atmosphere. Finite suppression of spurious sidemodes, optical linewidth, and instability of the comb has been examined to estimate potential wavelength biases in spectrograph calibration. Sidemode suppression varies between 20 and 45 dB, and the optical linewidth is approximately 350 kHz at 1550 nm. The comb frequency uncertainty is bounded by +/-30 kHz (corresponding to a radial velocity of +/-5 cm/s), limited by the global positioning system disciplined oscillator reference. These results indicate that this comb can readily support radial velocity measurements below 1 m/s in the near IR.

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Available from: Gabriel G. Ycas
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• "In this case, the uncertainty in the position of the comb teeth is determined by the combination of the uncertainty in the stabilization of ν o and the uncertainty of the microwave source that provides the modulation frequency f m . However, the typical uncertainty of a microwave source can be sub-Hertz when synchronized with a compact Rb clock and moreover can be GPSdisciplined to provide long-term stability (Quinlan et al. 2010). Thus, the dominant uncertainty in comb tooth frequency in the LR-EOFC is that of ν o . "
##### Article: Demonstration of a Near-IR Laser Comb for Precision Radial Velocity Measurements in Astronomy
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ABSTRACT: We describe a successful effort to produce a laser comb around 1.55 $\mu$m in the astronomical H band using a method based on a line-referenced, electro-optical-modulation frequency comb. We discuss the experimental setup, laboratory results, and proof of concept demonstrations at the NASA Infrared Telescope Facility (IRTF) and the Keck-II telescope. The laser comb has a demonstrated stability of $<$ 200 kHz, corresponding to a Doppler precision of ~0.3 m/s. This technology, when coupled with a high spectral resolution spectrograph, offers the promise of $<$1 m/s radial velocity precision suitable for the detection of Earth-sized planets in the habitable zones of cool M-type stars.
Full-text · Article · Jan 2015
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• "Field suitable references such as an Rb clock or a GPS disciplined oscillator can deliver frequency precision on the order of 1:10 -11 , a level of accuracy that corresponds to sub-cm/s RV offset. [22] The line spacing can be tailored through the use of high finesse Fabry–Pérot (FP) cavities to provide easily resolved, distinct calibration lines, and bandwidth can to a large degree be expanded to meet the spectrograph's requirements, yielding a calibration source with precision and long term stability that significantly exceed the ultimate precision of the spectrograph (for example, "
##### Article: A near infrared frequency comb for Y+J band astronomical spectroscopy
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ABSTRACT: Radial velocity (RV) surveys supported by high precision wavelength references (notably ThAr lamps and I2 cells) have successfully identified hundreds of exoplanets; however, as the search for exoplanets moves to cooler, lower mass stars, the optimum wave band for observation for these objects moves into the near infrared (NIR) and new wavelength standards are required. To address this need we are following up our successful deployment of an H band(1.45-1.7{\mu}m) laser frequency comb based wavelength reference with a comb working in the Y and J bands (0.98-1.3{\mu}m). This comb will be optimized for use with a 50,000 resolution NIR spectrograph such as the Penn State Habitable Zone Planet Finder. We present design and performance details of the current Y+J band comb.
Full-text · Article · Sep 2012 · Proceedings of SPIE - The International Society for Optical Engineering
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• "Therefore stabilization of the mode frequencies requires control over both degrees of freedom, repetition rate and offset frequency. There are many promising approaches to frequency-comb sources with multiple gigahertz mode spacing, including active and passive mode-locking of solid-state or fiber lasers [6] [7] [8] [9] [10] [11], cavity filtering [12] [13] [14], microcavities [15] [16] [17] and electro-optic modulation [18]. However, for many of the laserbased approaches, the pulse energy is too low to provide an octave-spanning spectrum, as required for self-referenced stabilization of the offset frequency [19] [20]. "
##### Article: Offset frequency dynamics and phase noise properties of a self-referenced 10 GHz Ti:sapphire frequency comb
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ABSTRACT: This paper shows the experimental details of the stabilization scheme that allows full control of the repetition rate and the carrier-envelope offset frequency of a 10 GHz frequency comb based on a femtosecond Ti:sapphire laser. Octave-spanning spectra are produced in nonlinear microstructured optical fiber, in spite of the reduced peak power associated with the 10 GHz repetition rate. Improved stability of the broadened spectrum is obtained by temperature-stabilization of the nonlinear optical fiber. The carrier-envelope offset frequency and the repetition rate are simultaneously frequency stabilized, and their short- and long-term stabilities are characterized. We also measure the transfer of amplitude noise of the pump source to phase noise on the offset frequency and verify an increased sensitivity of the offset frequency to pump power modulation compared to systems with lower repetition rate. Finally, we discuss merits of this 10 GHz system for the generation of low-phase-noise microwaves from the photodetected pulse train.
Full-text · Article · Sep 2011 · Optics Express