Photon total angular momentum manipulation

As an inherent degree of freedom,total angular momentum(TAM)of photons consisting of spin angular momentum and orbital angular momentum has inspired many advanced applications and attracted much attention in recent years.Probing TAM and tailoring beam’s TAM spectrum on demand are of great significance for TAM-based scenarios.We propose both theoretically and experimentally a TAM processor enabling tunable TAM manipulation.Such a processor consists of a set of quasi-symmetric units,and each unit is composed of a couple of diffraction optical elements fabricated through polymerized liquid crystals.Forty-two single TAM states are experimentally employed to prove the concept.The favorable results illustrate good TAM state selection performance,which makes it particularly attractive for high-speed large-capacity data transmission,optical computing,and high-security photon encryption systems.

Influences of atmospheric turbulence effects on the orbital angular momentum spectra of vortex beams

We investigate the atmospheric turbulence effects on orbital angular momentum(OAM) spectra of different kinds of vortex beams, including Laguerre–Gaussian(LG) beams and Bessel beams, numerically. We generate the holograms of atmospheric turbulence with different structure constants of the refractive index. The OAM spectra of distorted single-mode or multiplexed LG beams and Bessel beams are analyzed. Compared with the OAM spectra of the two kinds of vortex beams, the spectrum of the Bessel beams is more dispersive. The results illustrate that Bessel beams suffer more from turbulent atmosphere than LG beams.

Non-probe compensation of optical vortices carrying orbital angular momentum

In this paper, we demonstrate a scheme for compensating distorted optical vortex beams carrying orbital angular momentum. By inputting the intensity profile into the Gerchberg–Saxton algorithm [Optik 35, 237(1972)], the pre-compensation phase mask can be acquired. No additional probe beams are introduced, and all the computing is aiming at the transmitted vortex beams. The distorted vortex beams are investigated experimentally before and after pre-compensation, showing favorable compensation performance. This scheme will find applications in the areas of rotation detection, optical communications, and so on.

Demonstration of high-dimensional free-space data coding/decoding through multi-ring optical vortices

Multi-ring optical vortices are a kind of structured beams that carry orbital angular momentum(OAM) and have concentrical doughnut intensity distributions. In this Letter, we present both theoretically and experimentally a scheme that employs the dimensions of both the OAM states and radial index of multi-ring optical vortices simultaneously to accomplish high-dimensional free-space data coding/decoding transmissions. Such a scheme can further improve the coding efficiency when limited OAM states are available. In the proof-ofconcept experiment, 64-ary coding/decoding employing 16 OAM states and four radial indices are present. Also,the coding/decoding performance when facing various atmosphere turbulences is evaluated. Furthermore, a 64 × 64 gray image(totally, 32,768 bits) is also transmitted through multi-ring optical vortices coding in free-space successfully, showing good transmission performance.

1 kHz single-frequency, injection-seeded Er:YAG laser with an optical feedback

A novel 1 kHz single-frequency, Q-switched Er-doped yttrium aluminum garnet(Er:YAG) laser pumped by a 1470 nm laser diode is demonstrated. The 500 ns, 5.52 mJ single-frequency, diffraction-limited pulses are obtained by using a ‘ramp-fire' injection-seeding technique and an optical feedback architecture. The full width at half-maximum of the pulse spectrum is measured to be 1.47 MHz by using the heterodyne technique. The beam quality M2 factors are measured to be 1.18 and 1.24 in the x and y directions, respectively.

Experimental demonstration of generating arbitrary total angular momentum states

We experimentally demonstrated an approach to generate arbitrary total angular momentum(TAM) states by using two liquid crystal devices. Photons’ TAM, the sum of spin and orbital angular momenta(SAM and OAM)under paraxial approximation, has found many applications in optics and attracted increasing attention in recent years. Our approach is based on the orthogonality of two eigen SAM components, that arbitrary TAM states will be produced through encoding different holograms in one system. The comparison with theoretical predications yields an excellent agreement, including both the separable state and the non-separable state. The proposed scheme takes a step forward for generating complex structured fields and broadens its application to various fields like laser processing and large capacity data transmission.

Single-frequency Er:YAG ceramic pulsed laser with frequency stability close to 100 kHz

A single-frequency 1645 nm pulsed laser with frequency stability close to 100 kHz was demonstrated. The laser oscillator is injection-seeded by a single-frequency narrow linewidth Er∶Y_(3)Al_(5)O_(12)(Er:YAG) nonplanar ring oscillator and frequency stabilized by the modified Pound–Drever–Hall method. The pulse repetition rate can be set from 100 to 500 Hz with the frequency stability from 82.72 kHz to 134.44 kHz and pulse energy from 9.84 mJ to 19.55 mJ. To our knowledge, this is the best frequency stability of a single-frequency pulsed laser with injection-seeding.

Resonantly pumped 1645 nm Q-switched Er：YAG laser with a ring cavity

This paper report an 1645 nm Er：YAG laser resonantly pumped by an Er-fiber laser operating at 1532 rim. 1.78 W continous wave （CW） output power with a slope efficiency of 52% was obtained using a long ring cavity and an 1 at.% doped Er：YAG crystal. In Q-switched mode, the obtained pulse energy was 1.6 mJ at a repetition rate of 500 Hz; for 1 kHz repetition rate, 1.2 mJ output energy was obtained.