Instrument overview

Purpose and scope

CLASSI is a low-resolution, fiber-fed spectrograph for rapid optical spectroscopy at Mount Laguna Observatory. The instrument combines a telescope focal-plane fiber input, a compact bench spectrograph, a cooled scientific CMOS detector, an instrument control system, and a common set of planning, simulation, and reduction tools.

This page defines the system-level view used throughout the manual. Individual component specifications are collected in Instrument hardware; software interfaces are documented under Packages and services.

System at a glance

The light and data paths are:

sky -> telescope -> focal-plane fiber bundle -> fiber run
     -> collimator -> optional order-blocking filter -> reflection grating
     -> camera lens -> science detector -> raw FITS exposure
     -> calibration and extraction -> one-dimensional spectra

The principal spectrograph components are:

Principal optical and detector components

Subsystem

Component

System role

Fiber feed

Thorlabs FG105LVA, 105 µm core

Samples the telescope focal plane and defines the entrance-aperture scale.

Collimator

Thorlabs AC508-180-AB-ML, 180 mm EFL

Converts the diverging fiber output into the beam incident on the grating.

Order blocking

Removable Thorlabs FGL400S

Suppresses blue second-order contamination when installed.

Disperser

Newport 270R, master 1294, 300 grooves/mm

Produces the low-resolution spectrum in first order.

Camera optic

Canon EF 100mm f/2 USM

Images the dispersed beam onto the detector.

Science detector

FLI Aurora AR571, 6244 × 4168, 3.76 µm pixels

Records the two-dimensional fiber spectra.

These are component or configured values. Spectral coverage, resolution, throughput, trace locations, focus, and limiting sensitivity are properties of the assembled system and must ultimately be measured in commissioning.

Operational subsystems

CLASSI operation spans several connected subsystems:

  • the telescope and guide-side hardware, which place and hold the target on the fiber input;

  • the fiber feed and bench spectrograph, which transport and disperse the light;

  • the science camera and camera-lens controller, which set focus/aperture and acquire detector frames;

  • the instrument control system (ICS), which presents status and acquisition controls and writes science FITS files; and

  • the planning and reduction software, which predicts exposure performance and turns detector frames into calibrated spectra.

An observation is successful only when all of these layers are configured consistently. For example, the filter state, grating geometry, camera mode, detector temperature, and focus used at the telescope must agree with the configuration assumed during planning and reduction.

Primary data products

The raw science-camera FITS files are the authoritative record of an exposure. Browser displays, quick-look plots, ETC results, and simulated frames are derived or predictive products. A complete observing dataset should retain:

  • raw science and calibration frames;

  • the acquisition and instrument metadata written with those frames;

  • observing notes and any configuration changes made during the night;

  • reduction configuration and software versions; and

  • extracted spectra together with their uncertainties and masks.

Where to go next

Read Instrument and software architecture for the boundaries between physical, control, and software subsystems. Observers can then proceed to Planning an observation and Operating the instrument; instrument characterization belongs in Instrument hardware and the reference section.