A spectral imaging device for generating a spectral cube of a sample, the spectral imaging device having a desired spectral resolution, the spectral imaging device comprising: an image sensor that comprises a two-dimensional array of sensors that are used to construct a two-dimensional output image; a tunable light source that generates an illumination beam that follows a beam path from the tunable light source to the sample and from the sample to the image sensor, the illumination beam having a spectral width that is equal to or less than the desired spectral resolution; an optical assembly comprising a plurality of refractive elements (24A, 24B) that are positioned along the beam path between the tunable light source and the image sensor; and a control system that is configured to control the tunable light source to generate a set of discrete modulation optical frequencies about and through a target optical frequency in a period of optical frequency modulation resulting in an extrinsically broadened illumination beam providing a desired, time-averaged optical frequency distribution, the set of discrete modulation optical frequencies having a maximum optical frequency modulation, Δv modulation, which satisfies the following prescription: Δv modulation = ±ηΔv/2, where η is a constant having a value of greater than or equal to 0.1 and less than or equal to 100, and Δv is the desired spectral resolution, characterized in that the control system is configured to control the tunable light source to generate at least two cycles of the set of discrete modulation optical frequencies during the time the control system controls the image sensor to capture the output image. an image sensor that comprises a two-dimensional array of sensors that are used to construct a two-dimensional output image; a tunable light source that generates an illumination beam that follows a beam path from the tunable light source to the sample and from the sample to the image sensor, the illumination beam having a spectral width that is equal to or less than the desired spectral resolution; an optical assembly comprising a plurality of refractive elements (24A, 24B) that are positioned along the beam path between the tunable light source and the image sensor; and a control system that is configured to control the tunable light source to generate a set of discrete modulation optical frequencies about and through a target optical frequency in a period of optical frequency modulation resulting in an extrinsically broadened illumination beam providing a desired, time-averaged optical frequency distribution, the set of discrete modulation optical frequencies having a maximum optical frequency modulation, Δv modulation, which satisfies the following prescription: Δv modulation = ±ηΔv/2, where η is a constant having a value of greater than or equal to 0.1 and less than or equal to 100, and Δv is the desired spectral resolution, characterized in that the control system is configured to control the tunable light source to generate at least two cycles of the set of discrete modulation optical frequencies during the time the control system controls the image sensor to capture the output image.