Wideband ambient light rejection

Optical apparatus, comprising:

• an image sensor;
• objective optics, which are configured to collect and focus optical radiation over a range of wavelengths along a common optical axis toward a plane of the image sensor;
• a dispersive element, which is positioned to spread the optical radiation collected by the objective optics so that different wavelengths in the range are focused along different, respective optical axes toward the plane,
• wherein the dispersive element has a first tilt relative to the optical axis, and wherein the apparatus comprises a wedged lens, which is configured to focus the optical radiation with a second tilt, opposite to the first tilt.

A method for imaging, comprising:

• collecting and focusing optical radiation over a range of wavelengths along a common optical axis toward a plane of an image sensor;
• positioning a dispersive element to spread the collected optical radiation so that different wavelengths in the range are focused along different, respective optical axes toward the plane,
• wherein the dispersive element comprises a diffractive element, which comprises a grating, and wherein positioning the dispersive element comprises configuring the grating to direct a selected diffraction order onto the image sensor;
• and
• positioning an interference filter between the grating and the image sensor so as to block stray diffraction orders, other than the selected diffraction order, from reaching the image sensor.

A method for imaging, comprising:

• collecting and focusing optical radiation over a range of wavelengths along a common optical axis toward a plane of an image sensor;
• and
• positioning a dispersive element to spread the collected optical radiation so that different wavelengths in the range are focused along different, respective optical axes toward the plane,
• wherein positioning the dispersive element comprises applying to the dispersive element a first tilt relative to the optical axis, and wherein collecting and focusing the optical radiation comprises positioning a wedged lens to focus the optical radiation with a second tilt, opposite to the first tilt.

A method for imaging, comprising:

• projecting optical radiation at a target wavelength onto an object;
• collecting and focusing the optical radiation reflected from the object, along with background radiation over a range of wavelengths, toward a plane of an image sensor;
• positioning a dispersive element to direct the collected optical radiation so as to form a sharp image of the optical radiation at the target wavelength in the plane of the image sensor, while spreading the background radiation across the plane,
• wherein positioning the dispersive element comprises shifting a position of the dispersive element relative to the plane so as to select the target wavelength that is to be imaged sharply in the plane;
• and
• processing the sharp image captured by the image sensor while rejecting interference caused by the background radiation.