Laser scanning by rotating polarization gratings

Abstract

Laser beam scanning can be realized using two independently rotating, inline polarization gratings, termed Risley gratings, in a fashion similar to Risley prisms. The analytical formulas of pointing position as well as their inverse solutions are described. On this basis, the beam scanning is investigated and the performance of scanning imaging is evaluated. It is shown that the scanning function in 1D scanning evolves from a sinusoidal to triangular scan and the duty cycle increases rapidly as the ratio of grating period to wavelength is reduced toward 2. The scan pattern in 2D scanning is determined by the ratio k of the gratings' rotatory frequency. In imaging applications, when k tends toward 1 or -1, the scan pattern becomes dense and is inclined to be spiral or rose-like, respectively, which is desirable for the purpose of enhancing spatial resolution. There is a direct trade-off between spatial resolution and frame rate. The spiral and rose scanning enable multiresolution imaging, providing a preview of the scanned area in a fraction of the overall scan time, which is extremely useful for fast, real-time imaging applications.

Path optimization of cascaded prism scanning beam defined by the rotation prism coordinate system

“…15(a) below has coordinates (x; y), so that the distance of each city can be calculated by Eq. (20). After the distance that connects all cities is known, then determine the best path that must be taken from the initial city to return to the initial city, as shown in Fig.…”

“…For the beam scanning application involving rotating prisms, researchers have extensively explored beam scanning patterns, 11 , 12 providing a foundation for more intricate and precise scanning patterns and rotary control 13 . Studies have also focused on enhancing prism structures, including introducing a third prism to address blind spot and singularity issues, 14 , 15 using two pairs of prisms 16 , 17 for coarse-fine scanning, 18 employing a combination of material prisms to solve dispersion problems, 19 and utilizing grating prisms for multi-resolution imaging 20 . With fast response, high accuracy, compactness, and robustness, these scanners have been used in various applications, such as target search and identification, 21 large field-of-view imaging, 22 biomedical observation, 10 laser communication, 23 beam-scanning detection, 13 , 24 vision-based microassembly, 25 etc.…”

Research on the deflection characteristics of non-mechanical beams of liquid crystal phase retardation cascade polarization gratings

“…When the wavelength is constant, the grating period is inversely proportional to the deflection angle. PG has different diffraction characteristics depending on the polarization state of the incident light wave [23]. By changing the polarization state of the incident light, the polarization grating can adjust the energy distribution between ± 1 order.…”

Experimental versus simulated secondary scan patterns produced by a pair of Risley prisms

“…The latter category includes scanning systems with Risley prism, rotational [8][9][10][11][12][13][14][15], oscillatory [16], as well as in combinations of rotational and oscillatory prisms. Simple prisms are the most common, but doublets are also useful to minimize chromatic aberration [17], while other devices (for example with diffraction gratings [18]) are being explored.…”