Amplification of a radially polarised beam in an Yb:YAG thin-slab

Abstract

which utilise the intense longitudinal electric field produced by a strongly focused radially polarised beam. A remarkable feature of radially polarised beams is their ability to be focused to smaller spot sizes than linearly polarised beams, leading to applications in high-resolution imaging [3]. Material processing, such as the cutting and drilling of metals, is another area where these beams have attracted great interest. It has been shown that cutting efficiency can be 1.5-2 times higher using radial polarisation rather than circular polarisation [4], and drilling can be 1.5-4 times more efficient with azimuthal polarisation compared to linear and circular polarisation [5].Various methods of producing CV beams have been implemented over the decades. CV beam generation can be broadly divided into two distinct categories; intracavity and extracavity techniques. Intracavity techniques rely on a cavity design that ensures one polarisation, i.e. radial or azimuthal, is dominant over the other and is, therefore, emitted from the laser directly. One popular approach is to exploit thermally induced bi-focusing in host materials such as YAG to render the resonator unstable for one polarisation, or yield a lower threshold for one polarisation by virtue of having a more favourable spatial overlap with the inversion distribution [6]. Alternatively, intracavity elements to provide polarisation discrimination, such as calcite crystals [7], Brewster-angled axicons [8], conical Brewster prisms [9], grating mirrors [10], or nanograting waveplates [11] can be employed. Extracavity techniques typically convert more traditional polarisation states, such as linear or circular polarisation, into radial or azimuthal polarisation. This can be achieved interferometrically, through the combination of orthogonal linearly polarised HG 01 and HG 10 beams [12]. Alternatively, a spatially variable retardation plate can be used to convert linear polarisation to radial or azimuthal polarisation [13]. AbstractThe use of an Yb:YAG thin-slab architecture for amplification of a radially polarised beam at 1030 nm is investigated and shown to be a promising route for power scaling. The detrimental impact of the Gouy phase shift on radial polarisation purity is considered and a simple scheme for effective phase shift management to restore polarisation purity is presented. Preliminary experiments based on a double-pass amplifier configuration yielded an output beam with a high radial polarisation extinction ratio of 15 dB and no degradation in polarisation purity despite the non-axial symmetry of amplifier gain medium. At 50 W of launched pump power a small-signal gain of 7.5 dB was obtained for a 25 mW input, whilst 4.4 dB gain was obtained for a 1.45 W input. The prospects for further power scaling are discussed.

Amplification of a radially polarized beam in a thermally guiding ytterbium-doped fiber rod

“…The radial polarization purity was quantified by measuring the two-lobe intensity profile contrast after transmission through a linear polarizer as a function of angle of the polarizer [8,12]. Intensity values were sampled from CCD camera images in a circular path with a radius chosen such that the circular path crosses the intensity maxima of the two-lobe profile (see Fig.…”

“…This approach has the appeal that it decouples the issues of radial polarization selection from power scaling. Amplification of radially polarized beams in rod [11], slab [12], and thin-disk [13] gain medium geometries has been demonstrated, but with limited success owing to thermal effects or the need for complicated multi-pass architectures. Cladding-pumped fiber amplifiers have also been investigated in this context offering the potential for high power, high gain, and immunity from detrimental thermal effects [14].…”

Radially polarized 33 W emission from a double-pass Ho:YAG thin-slab amplifier

“…For the cutting of sheet metals, radially polarized light may achieve a cutting efficiency that is up to 1.5-2 times higher than a linearly polarized or circularly polarized beam [5]. Not surprisingly, scaling the average power of radially polarized beams to meet the needs of laser cutting applications has been the subject of much interest, with recent studies investigating different amplifier architectures (such as thermally-guiding fiber rods, single-crystal fibers, face-pumped thin-disks and edge-pumped thin-slabs [6][7][8][9]) in order to increase the power from a radially polarized master-oscillator whilst preserving the beam quality and radial polarization purity.…”

“…In addition, the thin-slab crystal can generally achieve a high level of gain extraction for efficient amplification without the need for a more complex multi-pass arrangement that is often utilized for thin-disk amplifiers. While the strong astigmatic focusing of a radially polarized beam into a thin-slab results in a distorted polarization profile due to the different phase shifts experienced by the constituent HG 01 and HG 10 modes, this can often be corrected after amplification with a half-wave plate [9]. However, when the pump power is increased, stress-induced birefringence in the thin-slab crystal will produce an additional phase shift between the orthogonally polarized components, further degrading the radial polarization purity.…”

Tailored optical potentials for Cs atoms above waveguides with focusing dielectric nano-antenna

“…More specific data from the simulations are shown in Table (1). We propose to illuminate the waveguide using the power scaling technique widely used in an integrated photonics: rare-earth dopants can be used on a segment of the waveguide to amplify the source in order to achieve the listed fields [26]. We can also disregard effects due to nonlinearity; the contribution of the nonlinear coefficient [27] reads as P ower×2.88 * 10 −7 , which is negligible compared to the total refractive index.…”