Wavefront and Field#

Lentil’s Wavefront class represents a discretely sampled electric field. Wavefronts in Lentil are monochromatic (i.e. they represent a single wavelength). A wavefront is defined by the following parameters:

wavelength - The wavefront wavelength
pixelscale - The physical sampling of the wavefront’s electric field
diameter - The outscribing diameter around the wavefront
focal_length - The focal length of the wavefront. A plane wave has an infinite focal length denoted by np.inf
tilt - A tuple of tilt angles about the x and y axes
ptype - The plane type of the wavefront

Wavefronts are mutable through interaction with a Plane. For more details see How a plane affects a wavefront.

Wavefonts have several useful attributes for working with their electric field:

field - returns the wavefront’s complex field
intensity - returns the intensity (modulus squared) of the wavefront’s complex field
shape - returns the shape of the wavefront’s complex field. If shape is (), the wavefront is considered infinite and will inherit any finite plane shape

ptype#

A wavefront’s type (ptype) defines how it interacts with a Plane. When a wavefront interacts with a plane, it inherits the plane’s ptype. Plane type is set automatically and unexpected behavior may occur if it is changed.

Wavefront support the following ptypes:

`none`	Wavefront has no specific type
`pupil`	Wavefront is at a pupil plane and has a finite focal length
`image`	Wavefront is at an image plane

The rules defining when a wavefront is allowed to interact with a plane based on ptype are described here.

How a plane affects a wavefront#

An optical plane generally has some effect on a wavefront as it propagates through the plane. A plane may change a propagating wavefront’s amplitude, phase, and/or physical extent. This Plane-Wavefront interaction is performed by the plane’s multiply() method. A Plane and Wavefront can be multiplied in two ways:

By calling Plane.multiply() directly:

>>> w1 = plane.multiply(w0)

By using the built-in multiplication operator (which in turn calls Plane.multiply()):

>>> w1 = plane * w0

The multiply() method constructs a complex phasor from the plane’s amplitude and opd attributes and the Wavefront wavelength. The plane complex phasor is then multiplied element-wise with the wavefront’s complex data array.

Multiplication rules#

The table below outlines when a wavefront can interact with a plane based on their ptype and what the wavefront’s pytpe is after interaction:

Plane `ptype`	Wavefront `ptype`
Plane `ptype`	`none`	`pupil`	`image`
`none`	`none`	Not allowed	Not allowed
`pupil`	`pupil`	`pupil`	Not allowed
`image`	`image`	Not allowed	`image`
`tilt`	`none`	`pupil`	`image`
`transform`	`none`	`pupil`	`image`

Field#

Lentil’s wavefront consists of two major components: electric field data and metadata about the wavefront. Internally Wavefront uses one or more Field objects to store the electric field data. Users shouldn’t need to interact with fields directly, but understanding how they are used helps to understand Lentil better.

A field is defined by the following parameters:

data - The complex eletric field data
pixelscale - The physical sampling of the electric field data
offset - The location of the center of the field data relative to the global optical axis at (0,0)
tilt - A list of Tilt objects [1]