EDI Milestones II

Spctrgrph. Stability Boosting

Spctrgrph. Lineshape Diagnose

Single-delay crossfading stabilization demonstrated on TEDI data (2021)

See Ref. 43.

EDI using Fabry-Perot illumination to diagnose lineshape asymmetry of Keck Planet Finder spectrograph (2022)

See Ref. 42.

Multiple-delay crossfading stabilization theoretically explored (2018-2021)

See Ref. 36.

EDI generated sine combs to diagnose resolution of Keck Planet Finder spectrograph during engineering tests (2022)

See Ref. 42.

After EDI resolution boosting was demonstrated, it was further realized that the EDI derived spectra were unusually resistant to wavelength drifts in the disperser, such as due to temperature variations, or changing gravity vector that slightly distort the position of the detector relative to the disperser grating or prism. It was realized that we could further enhance this stability by combining the EDI data of two different delay values, with special mathematical processing. With further thought, it was realized that even with a single delay, under certain circumstances, can be processed to produce enhanced stability (robustness against dimensional distortions of the disperser instrument).

EDI generated sine combs, to diagnose performance of Keck Planet Finder (KPF) spectrograph during engineering tests at UC Berkeley Space Sciences Lab., where the KPF was being assembled (spring 2022). The laser frequency comb purchased for the KPF was late on delivery, and there was an urgent need to measure optical performance during preliminary alignment. Our EDI was being tested in a nearby room, so we brought it over to the KPF to help. It turned out we learned a lot of interesting things about how an interferometer can diagnose a dispersive spectrograph, some of which we are still in process of writing up.

A single-delay stability technique could have great practical utility, such as stabilizing spectrographs on airborne platforms. These suffer from thermal and barometric changes, acceleration stresses, yet need to be compact and low weight.

EDI Milestones I

Doppler velocimetry

Resolution Boosting

10x resolution boost
of M-stars using 7 delays, at the Hale telescope (2007-11).

See Ref. 26.

Exoplanet discovery by Jian Ge's EDI
New exoplanet discovered by Jian Ge's EDI (2006)

6x resolution boost
from 25k to 140k, measuring iodine, using multiple delays (2003).

See Ref. 8.

Exoplanet measurement by Jian Ge's EDI
Planet detection around 51 Pegasi by Jian Ge's EDI (2004)

2x res single-delay boost of Lick echelle
Photos of EDI at Lick echelle and raw data (2002).

Processed single delay spectra having 2x boost (2003).

See Ref. 7.

First stellar EDI data
First stellar EDI measurements, at Lick 1m (1999)

For more info see Ref. 3

First resolution boost, 2.5x
2.5x boost on sunlight using a single delay (2001)

See Ref. 7.

Simple apparatus
Photograph of a benchtop EDI (1998-2001)

~1 m/s velocity precision
Benchtop velocity repeatibility tests using bromine-iodine (Mar 1999)

For more info see Ref. 1

First EDI Doppler (demo'd on sunlight)
Detection of 12 m/s tugging of Earth by the Moon via an inexpensive benchtop instrument (1998)

For more info see Ref. 4

Doppler velocimetry was the motivation for the 1997-2000 LDRD project that developed EDI, to aid the Doppler planet search. LLNL researchers had already many years of experience using an interferometer by itself with monochromatic (laser) illumination to measure Doppler velocities of terrestrial objects. For the LDRD project, the idea was to augment the interferometer with a disperser in series. This separated the wavelengths into many individually narrow bandwidth channels, each one producing fringes similar to the monochromatic laser illumination. This allowed high visibility fringes to be detected in spite of the broad bandwidth of starlight (which otherwise prevents strong signals on starlight).

After EDI velocimetry was demonstrated, it was realized that the same EDI data could be processed in a different way to extract details about the shape of the stellar spectrum. This would yield details at high spectral resolution that would normally be beyond the capability of the disperser used alone. Normally, high resolution requires physically larger dispersive spectrographs. Thus the EDI used in this Resolution Boosting mode is a way to perform high resolution spectroscopy over a wide bandwidth but using a smaller and lower cost instrument.