A method comprising: providing at least one imaging device defining at least one first focal plane (P y) and at least one second focal plane (P x), the at least one imaging device including at least one image sensor configured to capture one or more images of one or more scattered light signals (220, 222) scattered through Rayleigh scattering from at least one laser beam propagating through at least one sampling region, wherein the at least one imaging device includes at least one in-focus modulation transfer function H(ξ); providing at least one image processing module having at least one display capturing at least one in-focus image in the first focal plane (P y) of a first scattered light signal and at least one out-of-focus image in the second focal plane (P x) of a second scattered light signal with the at least one image sensor; generating one or more slices (270, 272, 274) of the scattered laser beam signals by scanning the at least one in-focus image with at least one cursor at one or more cursor positions (260, 262, 264); determining at least one first axis (B 1) of the at least one in-focus image in the at least one first focal plane (P y) with the at least one image processing module; computing a distance, d, from a center of each of the slices (270, 272, 274) to the second focal plane (P x), the center of a slice being the point on the first axis corresponding to the slice, and assigning values of the distances (d 270, d 272, d 274) from each respective slice (270, 272, 274), wherein the center of each of the slices (270, 272, 274) is defined relative to the at least one in-focus image 234a; determining at least one out-of-focus transfer function G(ξ,d) for each of the slices (290, 292, 294) in the out-of-focus image using the assigned values of the distances (d 270, d 272, d 274); deconvolving each slice (290, 292, 294) of the out-of-focus image against the in-focus modulation transfer function H(ξ) and the at least one out-of-focus transfer function G(ξ,d); and outputting at least one corrected image to the at least one display, and using the at least one corrected image to calculate a width of at least one beam waist shown in the corrected image. providing at least one imaging device defining at least one first focal plane (P y) and at least one second focal plane (P x), the at least one imaging device including at least one image sensor configured to capture one or more images of one or more scattered light signals (220, 222) scattered through Rayleigh scattering from at least one laser beam propagating through at least one sampling region, wherein the at least one imaging device includes at least one in-focus modulation transfer function H(ξ); providing at least one image processing module having at least one display capturing at least one in-focus image in the first focal plane (P y) of a first scattered light signal and at least one out-of-focus image in the second focal plane (P x) of a second scattered light signal with the at least one image sensor; generating one or more slices (270, 272, 274) of the scattered laser beam signals by scanning the at least one in-focus image with at least one cursor at one or more cursor positions (260, 262, 264); determining at least one first axis (B 1) of the at least one in-focus image in the at least one first focal plane (P y) with the at least one image processing module; computing a distance, d, from a center of each of the slices (270, 272, 274) to the second focal plane (P x), the center of a slice being the point on the first axis corresponding to the slice, and assigning values of the distances (d 270, d 272, d 274) from each respective slice (270, 272, 274), wherein the center of each of the slices (270, 272, 274) is defined relative to the at least one in-focus image 234a; determining at least one out-of-focus transfer function G(ξ,d) for each of the slices (290, 292, 294) in the out-of-focus image using the assigned values of the distances (d 270, d 272, d 274); deconvolving each slice (290, 292, 294) of the out-of-focus image against the in-focus modulation transfer function H(ξ) and the at least one out-of-focus transfer function G(ξ,d); and outputting at least one corrected image to the at least one display, and using the at least one corrected image to calculate a width of at least one beam waist shown in the corrected image.