Optics letters最新文献

In recent years, structured beams have emerged as an attractive and promising area of research, and nondiffracting beams and vector beams stand out as two particularly important categories of structured beams. Recognizing the significance of both beams, it is valuable to build a connection between these two kinds of structured beams. Here, we propose a kind of multi-periodic full Poincaré beam (MP-FPB), whose polarization states can cover the Poincaré sphere (PS) surface multiple times. A nondiffracting ring is generated by the MP-FPB in propagation, which can propagate without diffraction in a certain distance. The polarization of the nondiffracting ring is variant along the azimuthal direction, and the polarization is also stable in propagation. Additionally, the MP-FPB exhibits self-healing characteristics, with its nondiffracting ring demonstrating good self-reconstruction capability. The MP-FPB can enrich the family of the structured light, and the nondiffracting ring with self-healing ability makes the beam resist distortion and preserves the beam's shape. These features not only endow optical beams with exceptional robustness but also facilitate various applications such as optical communication, encryption, optical tweezing, high-resolution microscopy, and quantum informatics.

We demonstrate on a high-power 1-GHz Kerr-lens mode-locked (KLM) ytterbium (Yb):CYA laser delivering 149-fs pulses with an average power of 11.1 W. The corresponding single-pulse energy and peak power are 10.3 nJ and 60.8 kW, respectively. The mode-locking operation can be consistently sustained with root mean square (RMS) values of power fluctuations of only 0.52% for 100 min. To the best of our knowledge, this is the highest average power ever reported from a GHz femtosecond mode-locked oscillator.

Multiple coherent radiations are achieved in a water-3-aminopropanol (3AP) mixed solution through cascaded four-wave mixing (C-FWM) and cascaded Stokes (C-Stokes) processes, both driven by stimulated Raman scattering (SRS) in this work. The O-H vibration peak from water is replaced by the emergence of the -NH₂ symmetric stretching Raman peaks from 3AP, with intensity approaching that of the -CH₂ symmetric stretching peak. The dual-wavelength SRS signals for the -NH₂ and -CH₂ stretching vibrations have a relatively small frequency interval of about 400 cm^-1 (16 nm). By varying the 3AP concentration and pump energy, these two peaks from 3AP act as new pump sources, enabling the successful generation of up to 16th-order Stokes and 5th-order anti-Stokes radiation through C-FWM and C-Stokes processes. The resulting spectrum spans a broad wavenumber range from -3318 to 6629 cm^-1 (452 to 822 nm), offering a new approach for broadband coherent light sources and multi-order Raman spectra in liquid media.

We study experimentally the nonlinear mode coupling between circular polarizations in a vertical-cavity surface-emitting laser (VCSEL) device developed for spin injection. The specific experimental arrangement that includes a Faraday rotator enables laser oscillation on left-circular or right-circular polarization, by adjusting the cavity losses. We show the simultaneous oscillation of both polarizations never occurs, proving that the Lamb coupling constant is very close to 1 in this VCSEL device, a situation that is ideal for spintronic applications.

We show that the phase mismatch in LiB₃O₅ (LBO) crystals is approximately proportional to the temperature deviation from the phase-matching temperature of crystals. Moreover, a fixed temperature deviation would result in approximately the same amount of phase mismatch over a large range of wavelengths. Based on this, we demonstrate that the pulse characteristics of LBO-based femtosecond optical parametric oscillators (OPOs) can be tailored by simply tuning the crystal temperature. Experimentally, at a temperature deviation of 10°C, nearly transform-limited optical pulses were obtained over a tuning range of 780-910 nm, and at a temperature deviation of -9°C, linearly chirped pulses with broadened spectra were obtained, which were de-chirped to be nearly transform-limited ones outside the cavity. The capability of generating femtosecond pulses with different pulse characteristics and at various wavelengths would benefit many applications, including spectroscopy and Raman microscopy.

Fiber-form optics extends the high-resolution tomographic imaging capabilities of optical coherence tomography (OCT) to the inside of the human body, i.e., endoscopic OCT. However, it still faces challenges due to the trade-off between probe size, resolution, and depth of focus (DOF). Here we introduce a method for extending the DOF in endoscopic OCT with high uniformity and efficiency. On the basis of multi-level diffractive optics, we leverage the multi-dimensional light-field modulation capabilities of computer-generated holography (CGH) to achieve precise control of the intensity distribution of the off-axis portion of the OCT probe light. Our method eliminates the need for an objective lens, allowing for direct fabrication at the distal facet of a single-mode fiber using femtosecond laser two-photon 3D printing. The superiority of our method has been verified through numerical simulation, beam measurement, and imaging results obtained with our home-built endoscopic OCT system.

We report the excitation of optical anapole states at ultraviolet (UV) wavelengths. Numerical simulations indicate that TiO₂ nano-rectangles with varying length-to-width ratios can support such modes within the 350-380 nm range. We further propose a two-dimensional periodic arrangement of these nano-rectangles deposited atop a fused silica substrate. Understanding and manipulating optical anapole states in the ultraviolet spectrum is crucial for advancing next-generation photonic devices and enhancing nonlinear optical processes, such as generation of highly energetic vacuum ultraviolet light through third-harmonic generation.

Optical-resolution photoacoustic microscopy enables cellular-level biological imaging in deep tissues. However, acquiring high-quality spatial images without knowing the point spread function (PSF) at multiple depths or physically improving system performance is challenging. We propose an adaptive multi-layer photoacoustic image fusion (AMPIF) approach based on blind deconvolution and registration. Our findings indicate that the AMPIF method rapidly achieves optimized multi-layer focused fused images with superior resolution and contrast without relying on prior knowledge of the PSF. This method holds significant potential for fast imaging of living biological tissues with enhanced contrast at multiple imaging depths.

The development of efficient and long-lived halogen-free organic phosphorescent molecules remains a challenge. For the single-heteroatomic 9,10-dihydroacridine (AcH₂), the evolution of singlet and triplet excited state absorption signals reveals an intersystem crossing (ISC) lifetime of 8.2 ns and a triplet state lifetime of 0.52 µs. In contrast, the ISC lifetimes of di-heteroatomic phenoxazine (PXZ) and phenothiazine (PTZ) are significantly accelerated to 1.7 ns and 1.1 ns, respectively, while the triplet state lifetimes are extended to 0.72 µs and 4 µs. These results confirm that the introduction of di-heteroatomic synergistic effects enhances ISC efficiency while simultaneously prolonging the triplet state lifetimes. Notably, these two critical factors are further improved in PTZ due to the heavy-atom effect of sulfur atom. The work emphasizes the di-heteroatomic synergistic effect, particularly the role of heteroatoms with large atomic numbers, which is crucial for the design of halogen-free organic phosphorescent materials.

Polymer photonics is receiving significant attention due to its potential for a wide range of integrated photonic applications and wide wavelength transparency. Wafer-scale testing is challenging due to low-index contrast in polymer waveguides. In this Letter, we demonstrate an amorphous silicon based out-of-plane polymer waveguide grating coupler. Simulations predict a maximum efficiency of -1.13 dB, with a 1 dB bandwidth of 95 nm over the C-L-band. Experimentally measured peak coupling efficiency between a single-mode optical fiber and polymer waveguide is -2.15 dB per coupler with a 1 and 3 dB bandwidth of 49 and 89 nm, respectively.