We present a compact self-interference incoherent digital holography (SIDH) system that incorporates a quarter-waveplate (QWP)-based geometric phase (GP) lens to achieve high-fidelity, full-color holographic imaging under broadband incoherent illumination. Traditional SIDH systems that utilize half-waveplate (HWP)-based GP lenses are hindered by unavoidable triple-wavefront polarization interference, stemming from chromatic dispersion in phase retardation. This interference introduces color-dependent artifacts in the reconstructed images. In contrast, our QWP-based design inherently suppresses such interference by using the non-diffracted beam as the reference, enabling stable dual-wavefront modulation. This approach produces phase-encoded polarization interference patterns that remain spectrally consistent across the red, green, and blue (RGB) channels. Experimental results demonstrate substantial noise suppression and significantly improved full-color image fidelity, supported by channel-specific noise analysis and structural similarity metrics. The system also preserves a simplified optical configuration without active polarization control, allowing for compact integration and cost-effective fabrication. These advantages position the proposed QWP-GP SIDH architecture as a promising solution for portable, real-time digital holographic 3D imaging, with scalable potential in applications such as augmented reality, optical diagnostics, and spectral holography.

In this paper, a fast step heterodyne light-induced thermoelastic spectroscopy (SH-LITES) sensor using a high-frequency quartz tuning fork (QTF) with resonant frequency of ~100 kHz is reported for the first time. The theoretical principle of heterodyne LITES (H-LITES) signal generation is analyzed firstly, and an acetylene (C₂H₂) H-LITES sensor is established to verify its performance. Experimental comparisons between the high-frequency QTF and a standard commercial QTF with resonant frequency of ~32.768 kHz reveal that the high-frequency QTF exhibits a tenfold faster response time. Specifically, the H-LITES sensor with this QTF achieves a 33 ms measurement cycle, 90% shorter than commercial counterparts. Furthermore, The SH-LITES technique is proposed to further shorten the scanning time to 15 ms, which achieves the shortest LITES measurement time known to date. To demonstrate its advantages in dynamic gas detection, an H₂O-LITES system integrating both QTF types is constructed for real-time monitoring of H₂O concentration during different respiration patterns. Comparative measurements show that the SH-LITES more accurately captures dynamic H₂O concentration fluctuations during respiration, outperforming the commercial QTF-based H-LITES sensor in rapid response scenarios.

Second-harmonic generation (SHG) is a fundamental nonlinear optical process widely used in photonics; however, it is strictly forbidden in the bulk of centrosymmetric materials due to their inversion symmetry. Nevertheless, applying an external electric field breaks this inversion symmetry. It induces an effective second-order nonlinear response known as the electric-field-induced second-harmonic generation (EFISH) effect. This mechanism enables SHG in centrosymmetric media and provides a effective mechanism for electrically tunable nonlinear nanophotonics. Here, we present a comprehensive overview of the EFISH effect, covering the fundamentals, various material platforms (including bulk semiconductor crystals, ferroelectrics, van der Waals materials, and polymers), as well as diverse strategies for electric field engineering. We distinguish EFISH from related effects including current-induced SHG and the quantum-confined Stark effect, and highlight emerging applications of EFISH in tunable photonic devices, carrier dynamics probing, and nonlinear optical modulation across optical, electronic, and THz regimes. Finally, we outline key challenges and prospects for the future development of electrically controlled nonlinear optical systems.

Non-invasive glucose monitoring remains a key challenge due to the molecule's inherently weak Raman signal. While surface-enhanced Raman spectroscopy (SERS) offers potential, it often suffers from incomplete spectral coverage. A recent work using tip-enhanced Raman scattering (TERS) successfully captures glucose's complete vibrational fingerprint. This label-free approach paves the way for highly sensitive metabolite detection and future in vivo biosensing applications.

The sensitivity and quantification capability of surface-enhanced Raman scattering (SERS) substrates are mutually exclusive, because the ultrasensitive SERS sites (hottest spots) necessary for the sensitivity will significantly magnify the SERS signals of the analyte molecules and thus each of these molecules will be miscounted to be hundreds during the quantification process. We demonstrate a concept to circumvent the above contradiction by engineering a timeshare SERS platform capable of working at the quantitative or the sensitive mode on demand. The timeshare SERS platform was constructed by transferring a monolayer gold nanosphere film onto elastic substrates (e.g., hydrogel). The volume change of the hydrogel could adjust the inter-nanosphere distance, dynamically controlling the formation or extinction of the SERS hottest spots on the same SERS substrate without influencing the spatial distribution of the analyte molecules. The timeshare SERS platform without the SERS hottest spots showed strong quantification capability, while when equipped with a substantial number of the SERS hottest spots exhibited ultrahigh sensitivity. We demonstrated quantitative and ultrasensitive detection of various analyte molecules using the quantitative and the sensitive mode of the timeshare SERS platform, respectively. We opened an avenue towards designing SERS substrates with both high sensitivity and strong quantification capability.

Ultrasound neuromodulation offers a non-invasive approach to modulate neural activity in the central nervous system. Precise, minimally invasive devices capable of targeted stimulation remain limited. A 200 µm diameter fiber-optic photoacoustic emitter (FPE) was developed, coated with a MXene (Ti₃C₂T_x) and polydimethylsiloxane composite to generate controllable, broadband ultrasonic waves with high spatial precision. Using this FPE to stimulate the medial prefrontal cortex in mice, it was observed marked alleviation of acute social defeat stress-induced emotional stress, evidenced by reduced anxiety-like behavior and increased social interaction. This approach enables near-field, broadband, and tunable ultrasound neuromodulation with potential applications in treating neuropsychiatric disorders involving emotional regulation.