Structured Laguerre–Gaussian beams for mitigation of spherical aberration in tightly focused regimes

Abstract

Many laser applications utilise a focused laser beam having a single-lobed intensity profile in the focal plane, ideally with the highest possible on-axis intensity. Conventionally, this is achieved with the lowest-order Laguerre–Gaussian mode (LG00), the Gaussian beam, in a tight focusing configuration. However, tight focusing often involves significant spherical aberration due to the high numerical aperture of the systems involved, thus degrading the focal quality. Here, we demonstrate that a high-order radial LGp0 mode can be tailored to meet and in some instances exceed the performance of the Gaussian. We achieve this by phase rectification of the mode using a simple binary diffractive optic. By way of example, we show that the focusing of a rectified LG50 beam is almost insensitive to a spherical aberration coefficient of over three wavelengths, in contrast with the usual Gaussian beam for which the intensity of the focal spot is reduced by a factor of two. This work paves the way towards enhanced focal spots using structured light.

Direct Acceleration of an Annular Attosecond Electron Slice Driven by Near-Infrared Laguerre–Gaussian Laser

“…On the other hand, an electron slice can be concentrated within approximately 2 • (see Figure 1(d)) in the transverse direction because of the formation of a transverse potential well about the beam axis (x axis), thus concentrating the electron toward the center to a certain extent (see Figure 1(e)). The field structure formed in the transverse and longitudinal directions in our case is similar to the formation of plasma bubbles in LWFA [42,60] . The only difference is that the accelerating phase is ahead of the decelerating phase in the 'bubble', and the size is determined by the wavelength of the LG laser in our case.…”

“…1(e)]. The field structure formed in the transverse and longitudinal directions in our case is similar to the formation of plasma bubbles in LWFA [42,62]. The only difference is that the accelerating phase is ahead of the decelerating phase in the "bubble," and the size is determined by the wavelength of the LG laser in our case.…”

“…Now the highest intensity of the LG laser can reach up to 6.3× 10 19 W/cm 2 by using the reflected phase plate on the petawatt laser facility in experiments [26]. The relativistic LG laser is expected to open new doors for particle manipulation in the DLA regime, because the hollow intensity distribution of the LG laser may result in the formation of a transverse potential well about the beam axis, similar to the charge-separated field structure in the bubble regime of LWFA [42][43][44][45]. It is believed that electrons can be accelerated in a concentrated manner in a new type of "bubble" regime, to overcome some of the drawbacks of Gaussian-laser driven DLA to a certain extent [46][47][48][49][50].…”

Improving the beam quality factor (M2) by phase-only reshaping of structured light

“…1. There are means to mitigate these effects, including coherently combining multiple independent laser sources [18][19][20][21], interferometric beam correction [22], the use of correction optics [23][24][25][26] and custom laser cavities [27][28][29][30][31][32], but these are complex solutions with limited general applicability. External brightness enhancement by beam transformation has also proved limiting: it has been shown that the beam quality factor cannot be improved by binary diffractive optical elements [33], while demonstrations with single continuous phase elements [34,35] have so far resulted in a lossy or imperfect process, e.g., using a continuous spiral phase to convert a vortex beam into a Gaussian actually results in many higher-order radial modes and reduced power in the desired mode Fig.…”