FIELD

The present disclosure relates generally to fluorescent spectroscopy, and more particularly, to systems and methods for inspecting a surface using fluorescent spectroscopy.

BACKGROUND

Molecules of some compounds can be excited from a ground state to an excited state using a beam of light. During this excitation, individual molecules absorb photons and shortly thereafter emit light having a longer wavelength than the beam of light. This emission of light after absorbing a photon is referred to as fluorescence.

Fluorescent spectroscopy is an inspection technique that involves the analyzing the spectral distribution of light emitted by a sample due to fluorescence. In an example approach, a light source illuminates a sample, causing some of the molecules within the sample to fluoresce. A detector then measures characteristics of the fluorescence, such as the intensity and/or wavelength of the light emitted by the sample.

An emission spectrum of a sample can be generated by exciting a sample at a particular wavelength and measuring the relative intensity of fluorescence over a range of detection wavelengths. Additionally or alternatively, an excitation spectrum of a sample can be generated by measuring the relative intensity of fluorescence at a particular wavelength while the sample is excited over a range of excitation wavelengths.

SUMMARY

In one example, a system for inspecting a surface is described. The system includes a laser, an optical system, a gated camera, and a control system. The laser is configured to emit light at a wavelength that varies over time. The optical system includes at least one optical element, and is configured to direct light emitted by the laser to points along a scan line during a plurality of time intervals such that: the wavelength of the light directed to each point along the scan line varies from point to point within time intervals of the plurality of time intervals, and over the plurality of time intervals, light having each wavelength of a plurality of wavelengths is directed to each point along the scan line. The gated camera is configured to record a fluorescent response of the surface from the light having each wavelength of the plurality of the plurality of wavelengths at each point along the scan line. The control system is configured to control the wavelength of the light emitted by the laser and control gating of the gated camera.

In another example, a system for inspecting a surface is described. The system includes a laser, an optical system, a gated camera, and a control system. The laser is configured to emit pulses of light, with respective wavelengths of the pulses of light varying over time. The optical system includes at least one optical element, and is configured to direct light emitted by the laser to points along a scan line one point at a time. The gated camera is configured to record a fluorescent response of the surface from light having each wavelength of a plurality of wavelengths at each point along the scan line. The control system is configured to control the gated camera such that an aperture of the gated camera is open during fluorescence of the surface but closed during exposure of the surface to light emitted by the laser.

In another example, a method for inspecting a surface is described. The method includes causing a laser to emit pulses of light having respective wavelengths that vary over time. The method also includes directing, using at least one optical element of an optical system, a first pulse of light having a first wavelength to a first point along a scan line and a second pulse of light having a second wavelength to a second point along the scan line. In addition, the method includes recording, using a gated camera, a first fluorescent response of the surface to the first pulse of light and a second fluorescent response of the surface to the second pulse of light. Further, the method includes directing, using the at least one optical element, a third pulse of light having the first wavelength to the second point and a fourth pulse of light having the second wavelength to the first point. Still further, the method includes recording, using the gated camera, a third fluorescent response of the surface to the third pulse of light and a fourth fluorescent response of the surface to the fourth pulse of light.

The features, functions, and advantages that have been discussed can be achieved independently in various examples or may be combined in yet other examples further details of which can be seen with reference to the following description and figures.

