Long sequence single-exposure videography using spatially modulated illumination

Abstract

Frequency recognition algorithm for multiple exposures (FRAME) is a single-exposure imaging technique that can be used for ultrafast videography, achieved through rapid illumination with spatially modulated laser pulses. To date, both the limit in sequence length as well as the relation between sequence length and image quality are unknown for FRAME imaging. Investigating these questions requires a flexible optical arrangement that has the capability of reaching significantly longer image sequences than currently available solutions. In this paper we present a new type of FRAME setup that fulfills this criteria. The setup relies only on (i) a diffractive optical element, (ii) an imaging lens and (iii) a digital micromirror device to generate a modulated pulse train with sequence lengths ranging from 2 to 1024 image frames. To the best of the authors’ knowledge, this is the highest number of temporally resolved frames imaged in a single-exposure.

High-speed videography of transparent media using illumination-based multiplexed schlieren

“…A drawback with the FRAME technique is that the number of frames in the sequence is limited. However, it has previously been demonstrated that hundreds of signals can be multiplexed in this way 39 , and our results (Fig. 4 b) suggest that it could be sufficient with a Fourier space area as small as pixels ( corresponds to a filter radius of 50 pixels) to capture all relevant signal, while still avoiding cross-talk between signals.…”

“…This amplitude is either reduced by the sample through e.g. light extinction 38 , 39 or is increased due to e.g. fluorescence 43 .…”

“…For more details on the challenges—both concerning the illumination as well as the analysis—with multiplexing long video sequences, see Ref. 39 .…”

“…Hence, there is an inherent trade-off between the number of multiplexed images and the spatial resolution of the individual images associated with the technique. However, since for natural images most information is located close to the low frequency components in Fourier space, the losses can in practice be small, even for a large number of images 39 .

Figure 1 Illustration of the phase analysis process.

…”

3D mapping of polycyclic aromatic hydrocarbons, hydroxyl radicals, and soot volume fraction in sooting flames using FRAME technique

“…In FRAME, the spatial modulation is usually achieved by introducing a transmission Ronchi grating in the path of the conventional laser beam of homogenous intensity. The other means to spatially modulate the laser beam can be a digital micromirror device (DMD) [37] or a two-faceted optical component [38]. In FRAME, judiciously, each "coded" illumination probing a different species is sent from different angles towards the incident plane (usually cross-patterned for two species) for probing the sample (see Fig.…”