FIELD

The field is laser-induced luminescence imaging.

BACKGROUND

The search for life in the Solar System and understanding habitability on other planets are two of the major goals of NASA and the Astrobiology Institute. Mars and icy worlds, including Europa and Enceladus, are prime locations to search for extant life in the solar system. For example, the subsurface of Mars is a prime location to explore for evidence of life, and new missions to explore Martian caves with small rovers or drones have been envisioned. In addition, the surface and subsurface of icy moons of Jupiter and Saturn, including Europa and Enceladus, are considered locations of great interest to astrobiology. Future missions will likely explore the European surface and icy world subsurface oceans. These missions would greatly benefit from reconnaissance instruments that can guide the spacecraft and obtain or analyze samples in regions having concentrations of organic materials and possible biosignatures. To search for life on other worlds, new instruments must be developed that can detect such biosignatures. So far, undisputed biosignatures have not been discovered anywhere outside of Earth, and the lack of any clear biosignatures on Mars or ocean worlds suggests that biological materials may be rare on planetary surfaces. Moreover, difficulties persist in the development of these instruments; background signals from rocks, ice, etc., are often several orders of magnitude stronger than the signal of interest are present, and the observations are further compounded by the complexities of spaceflight and planetary science and exploration mission requirements. Thus, a need remains for improved approaches to detecting material characteristics and biosignatures.

SUMMARY

Examples of the disclosed technology include methods and devices capable of time-resolved luminescence imaging and Raman spectroscopy. Example instruments can be suitable for surveying of bio-organic matter on planetary surfaces, including Mars and icy bodies in the solar system. Specific examples are capable of ppm level detection of luminescent organics in a survey mode, and ppb level detection of luminescent organics in a targeted mode. Instrument examples are also capable of determining major mineral phases using Raman spectroscopy.

According to an aspect of the disclosed technology, apparatus include divergence optics removably coupled to receive a probe beam in a first imaging mode to cause the probe beam to diverge before impinging on a first area of a target surface, and to not receive the probe beam in a second imaging mode to cause the probe beam to impinge on a second area of the target surface smaller than the first area, collection optics configured to receive, in response to the probe beam, luminescence light emitted from the first area and spectral light emitted from the second area, and an optical detector coupled to the collection optics, wherein the optical detector includes a luminescence imaging detector portion and a spectral imaging detector portion adjacent to the luminescence imaging detector portion, wherein the luminescence imaging detector portion is configured to receive the luminescence light emitted from the first area and the spectral imaging detector portion is configured to receive the spectral light from the second area. In some examples, the divergence optics include a lens, reflector, diffuser, or a combination, wherein the divergence optics are configured to produce a conical divergence in the probe beam of at least 5°. In some examples, the divergence optics include a beam homogenizer configured to reduce a nonuniformity of the intensity distribution of the probe beam. Some examples further include an actuator coupled to the divergence optics and configured to move at least a portion of the divergence optics from a path of the probe beam so that the probe beam is directed to the target surface without being imparted with a beam divergence with the divergence optics. Some examples further include a controller coupled to the actuator and configured to control movement of the divergence optics based on an imaging mode command. In some examples, the actuator can include a lens wheel or a movement stage. In some examples, the collection optics include spectrometer optics configured to receive a portion of the luminescence light or the spectral light and to disperse and direct the portion to the spectral imaging detector portion of the optical detector. In some examples, the spectrometer optics comprise a pick-off mirror, slit, diffraction grating or grism, and one or more focusing lenses. Some examples further include a pulsed laser source configured to produce the probe beam and to direct the probe beam along a probe beam path, wherein the divergence optics are removably coupled to the probe beam path to receive the probe beam and produce the divergence in the first imaging mode. Some examples further include a pulse generator coupled to the pulsed laser source and the optical detector and configured to control the generation of pulses by the pulsed laser source, wherein the optical detector is gated in relation to a timing of the pulse generator. In some examples, the optical detector is part of a detection unit that includes a detection intensifier configured to amplify a signal of the collected luminescence light and spectral light, wherein a gate timing of the detection intensifier is determined relative to the generation of pulses. In particular examples, the pulsed laser source is configured to emit laser pulses at a wavelength between 10 nm and 10 μm. Some examples further include a standoff configured to provide a predetermined distance between the divergence optics and the target surface in the range of 10 cm to 10 m, or a high f-number, fixed focus lens configured to provide a large depth of field. In some examples, the optical detector is an intensified time-gated detector. In some examples, the optical detector comprises a CCD, EM-CCD, fast-gated CMOS, and/or APD. In some examples, the optical detector is configured to detect luminescence and/or Raman spectral signatures. Some examples further include an optical filter configured to block at least a portion of scattering probe beam light from reaching the optical detector to reduce a damage to the detector and/or reduce a saturation of the detector that would hinder detection of the luminescence light and/or spectral light. In some examples, the optical filter includes a notch filter and/or long-pass filter. Some examples can include coupling optics configured to direct the probe beam to the target along a co-boresight path of the collection optics. Further examples can include beam adjustment optics configured to receive the probe beam along the co-boresight path in the first imaging mode and to adjust a direction of the probe beam to be approximately coaxial or parallel with an optical axis of the collection optics.

According to another aspect of the disclosed technology, methods include, in a first mode configured to detect laser induced luminescence: emitting a first laser pulse, directing the first laser pulse to a target surface with a divergence in the first laser pulse so that the first laser pulse diverges before impinging on a first area of a target surface, collecting an emission from the first area caused by the first laser pulse, and detecting a first luminescence image at a luminescence imaging detector portion of an optical detector and a first spectral image at a spectral imaging detector portion adjacent to the luminescence imaging detector portion; and in a second mode configured to detect Raman emission: emitting a second laser pulse, directing the second laser pulse to the target surface without the divergence associated with the first laser pulse so that the second laser pulse impinge on a second area of the target surface smaller than the first area, collecting an emission from the second area caused by the second laser pulse, and detecting a second spectral image at the spectral imaging detector portion. In some examples, the second mode is configured to detect a luminescence emission that is weaker than the laser induced luminescence from the first mode, using the luminescence imaging detector portion.

The foregoing and other features and advantages of the disclosed technology will become more apparent from the following detailed description, which proceeds with reference to the accompanying figures.

