arXiv subjects

Songlin Zhuang

Publications and source records attributed to Songlin Zhuang.

27 records · Page 2Linked to original sources

arXiv2021

Extraction of inherent polarization modes from a single light beam

Superposition of two independent orthogonally polarized beams is a conventional principle of creating a new light beam. Here, we intend to achieve the inverse process, namely, extracting inherent polarization modes from a single light beam. However, inherent polarization modes within a light beam are always entangled so that a stable polarization is maintained during propagation in free space. To overcome this limitation, we report an approach that breaks the modulation symmetry of a light beam, thereby disentangling the inherent polarization modes. Using polarization mode competition along with an optical pen, polarization modes are extracted at will in the focal region of an objective lens. This work demonstrates polarization mode extraction from a light beam, which will not only provide an entirely new principle of polarization modulation but also pave the way for multidimensional manipulation of light fields, thereby facilitating extensive developments in optics.

physics.optics↗

arXiv2021

Estimation of transmitted wavefronts at defocused positions in a broad bandwidth range

Wavefront aberrations can reflect the imaging quality of high-performance optical systems better than geometric aberrations. Although laser interferometers have emerged as the main tool for measurement of transmitted wavefronts, their application is greatly limited, as they are typically designed for operation at specific wavelengths. In a previous study, we proposed a method for determining the wavefront transmitted by an optical system at any wavelength in a certain band. Although this method works well for most monochromatic systems, where the image plane is at the focal point for the transmission wavelength, for general multi-color systems, it is more practical to measure the wavefront at the defocused image plane. Hence, in this paper, we have developed a complete method for determining transmitted wavefronts in a broad bandwidth at any defocused position, enabling wavefront measurements for multi-color systems. Here, we assume that in small ranges, the Zernike coefficients have a linear relationship with position, such that Zernike coefficients at defocused positions can be derived from measurements performed at the focal point. We conducted experiments to verify these assumptions, validating the new method. The experimental setup has been improved so that it can handle multi-color systems, and a detailed experimental process is summarized. With this technique, application of broadband transmission wavefront measurement can be extended to most general optical systems, which is of great significance for characterization of achromatic and apochromatic optical lenses.

physics.optics↗

arXiv2021

Establishment of the fundamental phase-to-polarization link in classical optics

Vector polarization induced by a change in scalar phase has been far beyond our understanding of the relationship between polarization and phase in classical optics due to the entanglement of inherent polarized modes of light beams. To overcome this limitation, we establish this miraculous relationship by the principle of phase vectorization, which can transform three particular phases into linear, circular and elliptical polarizations. A polarized-spatial light modulator based on the principle of phase vectorization can be achieved using a phase-only spatial light modulator, which not only enables pixel-level polarization manipulation of light beams in a real-time dynamic way but also simultaneously retains complete phase control. This work demonstrates the phase-to-polarization link and reports the creation of polarized-spatial light modulator, which will transform our view of the natural properties of light beam and pave the way for the era of vector optics.

physics.optics↗

arXiv2019

Lasing without population inversion in air

A cavity-free laser in the sky could lead to revolutionary improvements in optical remote sensing for atmospheric science. Abundant in air, nitrogen molecules are prime candidates as an active medium for such a laser. Nitrogen molecules, either neutral or singly ionized, exhibit a significant optical gain in the UV regime when pumped by an intense femtosecond laser. Despite numerous works, the physical origin of this lasing is still not understood. Here we offer a consistent interpretation of all experimental facts by introducing a concept drawn from the field of quantum optics: transient lasing without inversion. Our experiments and simulations identify the crucial role of macroscopic coherence, instead of population inversion, in the nitrogen ions lasing system. Manipulating the macroscopic coherence provides a new level of control over nitrogen air lasing and offers new perspectives for the generation of very short wavelength laser where population inversion is difficult to achieve.

physics.optics↗

arXiv2018

Coherent control of superradiance from nitrogen ions pumped with femtosecond pulses

Singly ionized nitrogen molecules in ambient air pumped by near-infrared femtosecond laser give rise to superradiant emission. Here we demonstrate coherent control of this superradiance by injecting a pair of resonant seeding pulses inside the nitrogen gas plasma. Strong modulation of the 391.4 nm superradiance with a period of 1.3 fs is observed when the delay between the two seeding pulses are finely tuned, pinpointing the essential role of macroscopic coherence in this lasing process. Based on this time-resolved method, the complex temporal evolution of the macroscopic coherence between two involved energy levels has been experimentally revealed, which is found to last for around 10 picoseconds in the low gas pressure range. These observations provide a new level of control on the "air lasing" based on nitrogen ions, which can find potential applications in optical remote sensing.

physics.optics↗

arXiv2018

Free-space creation of ultralong anti-diffracting light beam with multiple energy oscillations adjusted using optical pen

A light beam propagating with an infinite anti-diffracting distance requires infinite power to preserve its shape. However, the fundamental barrier of finite power in free space has made the problem of diffraction insurmountable over the past few decades. Here, to overcome this limitation, we report an approach that employs the multiple energy oscillation mechanism, thereby permitting the creation of a light beam with an ultralong anti-diffracting distance in free space. The anti-diffracting distance is no longer restricted by finite power in free space but instead depends on the number of energy oscillations. This unprecedented propagation behavior is attributed to a new understanding of non-diffractive light beam: when an anti-diffracting light beam completely discharges its energy, it cannot recharge again. A versatile optical pen is therefore developed to manipulate the number, amplitude, position and phase of energy oscillations for an arbitrary numerical aperture of a focusing lens so that energy recharge can occur in free space and multiple energy oscillations can be realized. A light beam with a tunable number of energy oscillations is eventually generated in free space and propagates along a wavy trajectory. This work will enable extending non-diffractive light beams to an expanded realm and facilitate extensive developments in optics and other research fields, such as electronics and acoustics.

physics.optics↗

arXiv2015

Influence of surface termination on inverse Goos-Hänchen shift of negatively refractive photonic crystals

The effect of surface termination on the inverse Goos Hanchen (GH) shift of two dimensional (2D) negatively refractive photonic crystal (NRPhC) containing air holes arranged in hexagonal lattice in a dielectric background is investigated for TM polarization. Results show that the magnitude of the inverse GH shift of 2DNRPhC strongly depends on surface termination even for an incident beam with a fixed frequency and incidence angle. Further study by calculating the dispersion of surface mode of 2D-NRPhC as a function of surface termination reveals that 2DNRPhC presents large inverse Goos Hanchen shift at those terminations where surface mode is excited, that is, large inverse Goos-Hanchen shift originates from backward surface mode of 2DNRPhC. In addition, the coupling coefficient of incident field into the field of surface mode as a function of surface termination is studied and demonstrates above results. This paper provides technical information regarding the combination of various functional photonic elements in the design of integrated optical circuits.

physics.optics↗

arXiv2015

Nonlocal effective medium approximation for metallic nanorod metamaterials

We present an analytical nonlocal effective medium approximation to describe the optical nonlocal effects in metallic nanorod metamaterials based on Mie scattering theory. It is shown that the developed nonlocal effective medium theory can predict a coexistence state of two modes around the epsilon-near-zero region, where strong optical nonlocal effects lead to the behavior of both positive refraction and negative refraction in the nanorod metamaterials. Outside of the coexistence region, only one mode can be excited and its behavior can be well described using the local effective medium theory.

physics.optics↗

arXiv2015

Energy flux pattern of inverse Goos-Hanchen shift in photonic crystals with negative index of refraction

The energy flux patterns of inverse Goos-Hanchen (GH) shift around the interface between air and negatively refractive photonic crystal (NRPhC) with different surface terminations is investigated. Results show that NRPhC exhibits inverse GH shift in TM and TE polarization, and the localization and pattern of energy flux differ in TM and TE polarizations and are strongly affected by surface termination. This is different to the condition of negative permittivity materials (i.e., metal), which only presents inverse GH shift in TM polarization. In the case of TE polarization, the energy flux pattern exhibits the flux of backward wave whose localization changes from the surface to inside of NRPhC with the variation of surface termination. In the case of TM polarization, the energy flux pattern is always confined within the surface of NRPhC, whereas its pattern changes from the flux of backward wave to vortices at the surface of NRPhC, which is different to the energy flux of TM polarization of metal. By properly truncating the surface of NRPhC we can control the magnitude of inverse GH shift for TM and TE polarized light.

physics.optics↗