Tutorials

Image Quality: Strehl Ratio & the Marechal Approximation

An ideal imaging system delivers a perfect, converging, spherical wavefront where the optical path length (OPL) along all rays from a given object point to the corresponding point on the...

Modal Noise in Optical Fibers & Ball Lens Couplers

Multimode fibers are conveniently used with low spectral resolving power. However, as spectral resolution increases modal noise in fibers introduces systematic errors in fiber-fed spectrographs. Here we summarize the origin...

Spectrometer Wavelength Calibration: Practice

A dispersive spectrometer encodes wavelength as position on a detector array. The raw data from a spectrometer is a list of pixel index with associated intensity. The process of wavelength...

Spectrometer Wavelength Calibration: Theory

A prism- or a grating-based dispersive spectrometer images the entrance slit (or fiber) onto a sensor where position in the image plane encodes wavelength. Commercial fiber fed spectrometers typically provide...

Non-linearity in Silicon Photomultipliers (SiPMs)

The linear regime for a SiPM cannot extend without limit because an APD is "blind" for some period after detecting a photon and above some intensity it will fail to detect...

Johnson Noise & the Transimpedance Amplifier

Generally, noise is any unwanted signal such as interference from a switching power supply or a WiFi router. These types of external noise can often be reduced or even eliminated...

Do Photons Exhibit Poisson Fluctuations?

Photons are not classical objects. Their behavior is governed by quantum statistics. At short wavelengths, Poisson counting is a good approximation. At infrared and radio wavelengths, the Poisson approximation breaks...

Using a Shear Plate Interferometer

In this video, we'll show you how to use a shear plate interferometer and interpret the measurements. We'll measure the focal length of a lens and show that it is...