(Caltech) Photonics & LNSD Club

Organizers: S. R. Kulkarni, D. Mawet and N. Jovonic

Background. The large radio telescopes of the past have given way to large collection of small telescopes. The switch from small number & large diameter (SNLD) to large number and small diameter (LNSD) was made possible by decreasing costs of low noise receivers, vast increase in digital processing and a cost curve for telescopes that increases with telescope area faster than the area.

In optical astronomy, technological forces are similarly favoring LNSD over SNLD for many goals. Optical sensors (CMOS) with very low read noise are now available at low cost. The amateur community has a huge appetite for low-cost but high performance telescopes, mounts, low noise detectors and sophisticated imaging data reduction tools. The deepest narrow band images are now being produced by amateur astronomers, thanks to, in addition to the above advances, low cost high-performance narrow band (3-nm brick wall) filters. The annual sales of the amateur community is now estimated to be $350M.

Time domain astronomy (TDA) is now a major force in optical astronomy. In fact, it appears that there is an over abundance of optical TDA imaging surveys. The real bottleneck is follow up, specifically spectroscopic follow up.

The primary workhorse for spectroscopic follow up is conventional spectrographs on moderate to large telescopes (for example, X-Shooter at VLT, NPGS on P200). There is a great opportunity to re-purpose existing 2-m to 3-m telescopes for TDA followup (for example, SEDM on P60, SOX on the 3.6-m NTT). Failing that new telescopes can be built for this purpose. Regardless, current spectrographs follow a conventional path (collimator, disperser, camera lens, detector). Conventional Spectrometers are not cheap. Reducing the cost of spectrographs is clearly of great value.

Separately, AO is extremely helpful for small telescopes, and as shown by Robo-AO, is affordable. Particularly for spectroscopy AO can lead to smaller fiber beams and so provide higher spectral resolution or more compact spectrographs. Finally, there has been very little discussion of amplitude interferometry based on fibers as opposed to free space propagation (cf. CHARA).

In this year-long exercise, we will review technologies related to

Participants are expected to be true to the spirit and framework of the Club. Specifically, they are expected to read the prescribed list of papers before (or/and after) the meeting. During the meeting, participants are expected to listen to the talk and not multi-task (as in catching up on emails). Each session will last 2 hours: 1 hour of talk and 1 hour of Q&A. We expect two talks per month. So, participants have to allocate a minimum of 8 hours per month.

Legalese: By joining the Club participants have explicitly allowed the organizers to record the talk and Q&A.

Editing Trail: [Look here for changes, usually additions.]
First version is dated 4 July 2026.
  1. Wide-field Imaging
  2. Low Surface Brightness Imaging
  3. Spectroscopic_Arrays.html
  4. Photonics
  5. AO for small telescopes
  6. Long-baseline interferometry, but fiber based

Lectures

In summer, the lecture slot is 1-3p, Friday (Pacific). You will be informed of the time for the lecture and Zoom link via email. Each lecture, if uninterrupted, is 45 minutes (45 slides). The talks & Q+A will be recorded and linked to this portal.
  1. August 7, 2026. Introduction to photonics (Nem Jovanovic)  |  talk & pptx

  2. August 14, 2026. Why LNSD? (Shri Kulkarni)  |  talk |  talk-pdf  |  Photons & Waves |  Mapping Speed |  Optical LNSD
    pptx has to downloaded and played locally on your machine

  3. August 21, 2026. MOTHRA by Roberto Abraham & Pieter van Dokkum  |  Helix Nebula (Advanced reading)  |  recording (incomplete)

  4. August 28, 2026. Photonic Lanterns by Yoo-Jung Kim  |  talk  |  pptx
    Zoom recording (incomplete)
    pptx file is too big to play in Google. Download it on your desktop.

  5. September 4, 2026, AMASE by Renbin YAN, Chinese University of Hong Kong. Note the time is 4-6p.
    talk |nbps

  6. September 11, 2026. Intensity Interferometry by Nick Konidaris, Carnegie.

  7. September 18, 2026. AO for small telescopes by Richard Dekany & Chris Baranec, UH

  8. September 25 2026. MAST & LAST by Earn Ofek, Weizmann

  9. October 2, 2026. Amplitude Interferometry by John Monnier, University of Michigan

  10. October 9, 2026. GOTTA by Jifeng Liu, NAOC, China   Note the time is 4-6p

  11. October 30, 2026.The beginnings of LNSD in space by Aaron Tohovahohu