The Keck Planet Finder will be a stabilized, fiber-fed, high-resolution (R~90,000) spectrometer with a broad spectral grasp (445-870 nm) across two cameras. The spectrometer has a well-proven asymmetric white pupil design, with an R4 echelle disperser and a VPH grism cross-disperser. The design includes a green channel (445nm to 600nm) and red channel (600nm to 870nm). A supplementary UV spectrometer (385–405nm) will capture the Ca II H & K lines at low resolution to monitor stellar magnetic activity.


Beam tracing of the optical path inside the KPF spectrometer.


Fed by the 10 m Keck I telescope, KPF is built for both high precision and high efficiency. Long-term radial velocity (RV) precision requires long-term instrumental stability and the ability to calibrate out short-term effects.  The desire for high Doppler precision (30 cm/s goal, 50 cm/s requirement) thus motivates the meticulous overall design. Thermomechanical stability is enabled by a low-expansion Zerodur bench, mounts, and optics, enclosed within a vacuum chamber and thermal enclosure. Optical stability, on the other hand, is enabled by a highly scrambled and agitated fiber feed, and the careful optical design of the instrument itself. In addition, simultaneous wavelength calibration will be performed during operationfor KPF using a stabilized Fabry-Perot etalon, with reference to a suite of hollow-cathode emission lamps.


The KPF vacuum chamber. The chamber is 1960 mm in diameter and 2600 mm long. The safety bumpers constrain excessive bench movement but are not in constant contact with the bench.


Instrument Highlights

  • R ~ 90,000
  • 2 channels: 444-590nm, 590-870nm
  • Fiber fed with macroscopic scrambler and agitator
  • Image slicing (x3) for maximum throughput
  • Zerodur-based optomechanical design for maximum stability
  • Asymmetric white pupil optical design
  • Echelle disperser, VPH grism cross-disperer
  • Vacuum chamber + thermal enclosure for environmental control
  • Chromatic exposure meter
  • Separate Ca H&K spectrometer
  • On 10m Keck – extreme precision + efficiency in Northern Hemisphere
  • Leverages long history of CPS + HIRES exoplanet discovery