On 14 November 2025,I will formally step down as Co-Editor-in-Chief of Light:Science & Applications.This decision,reached after lengthy discussions with the administrators at the University of Rochester,our Research Security Officer and our Global Operations Director,aligns with my forthcoming institutional responsibilities.

Low-temperature phase (β-form) barium borate (BBO) is one of the most important nonlinear crystals that has been widely used for optical second-harmonic generation (SHG), especially with femtosecond sources. There was growing interest in its applications in the direct generation of terahertz (THz) radiations, but it was hindered by the lack of knowledge of its basic properties in the THz range. In a recent study based on first-principles quantum chemistry calculation, we found that the theoretically calculated refractive indices of β-BBO in the THz frequency range do not agree with the previously reported values. To explore the discrepancy between measured and calculated results, we grew and cut β-BBO crystals and performed independent experimental measurements on the refractive indices of BBO crystals. The new data show that the order of ordinary and extraordinary index of β-BBO in the THz range is opposite, contrary to several papers previously reported. Based on the newly acquired material properties, simple geometries fulfilling phase matching (PM) conditions with n o(THz)=n o g r(800nm) for efficient generation of THz radiation through optical rectification in β-BBO are proposed.

Terahertz (THz) dual-comb spectroscopy (THz-DCSS) is a competitive spectral technique due to its high frequency resolution. However, because the pump and detection femtosecond (fs) pulses are from two stabilized fs lasers, the perfect mutual coherence is difficult to reach, which prohibits long time data average and improving frequency resolution. Here, two frequency noise sources, the residual unlocked and transferred ones are investigated for a THz dual comb spectrometer (THz-DCSM). In time domain, the amplitude noise plays a dominate role on the performance of THz-DCSS; the repetition-frequency noises are negligible within Fourier-transform frequency resolution. In frequency domain, the relative synchronization error originating from the instantaneous frequency differences between the two fs lasers is 4 x 10(-13) (Delta f/f); the relative frequency resolution is similar to 4 x 10(-10), limited by the radio frequency reference. Our investigations are helpful for improving the performance of THz-DCSS and developing high frequency resolution THz spectroscopy.

As Co-Editors-in-Chief of Light:Science & Applications(LSA),we are honored to reflect on the journal's illustri-ous history,celebrate its achievements in 2024,and out-line our ambitious vision for the future.Launched in March 2012 by the Changchun Institute of Optics,Fine Mechanics and Physics,Chinese Academy of Sciences,and the Chinese Optical Society,in partnership with Nature Portfolio,LSA has become a global leader in optics and photonics research.With over 12,000 submissions and 2,200 publications from more than 70 countries and 1500 affiliations,LSA's impact is undeniable,boasting a Journal Impact Factor of 23.4(JCR 2024),ranking it among the top optics journals worldwide.

Atom-cavity systems offer unique advantages for building large-scale distributed quantum computers by providing strong atom-photon coupling while allowing for high-fidelity local operations of atomic qubits. However, in prevalent schemes where the photonic state is encoded in polarization, cavity birefringence introduces an energy splitting of the cavity eigenmodes and alters the polarization states, thus limiting the fidelity of remote entanglement generation. To address this challenge, we propose a scheme that encodes the photonic qubit in the frequency degree-of-freedom. The scheme relies on resonant coupling of multiple transverse cavity modes to different atomic transitions that are well-separated in frequency. We numerically investigate the temporal properties of the photonic wavepacket, two-photon interference visibility, and atom-atom entanglement fidelity under various cavity polarization-mode splittings and find that our scheme is less affected by cavity birefringence. Finally, we propose practical implementations in two trapped ion systems, using the fine structure splitting in the metastable D state of ^40Ca^+, and the hyperfine splitting in the ground state of ^225Ra^+. Our study presents an alternative approach for cavity-based quantum networks that is less sensitive to birefringent effects, and is applicable to a variety of atomic and solid-state emitter-cavity interfaces.

Inference of joule-class THz radiation sources from microchannel targets driven with hundreds of joule, picosecond lasers is reported. THz sources of this magnitude are useful for nonlinear pumping of matter and for charged-particle acceleration and manipulation. Microchannel targets demonstrate increased laser–THz conversion efficiency compared to planar foil targets, with laser energy to THz energy conversion up to ∼0.9% in the best cases.

We present a single-shot detection method of terahertz-correlated second harmonic generation in plasma-based sources by directly mixing an optical probe into femtosecond laser-induced plasma filaments in air. The single-shot second harmonic trace is obtained by measuring second harmonic generation on a conventional CCD with a spatio-temporally distorted probe beam. The system shows a spectrometer resolution of 22 fs/pixel on the CCD and a true resolution on the order of the probe pulse duration. With considerable THz peak electric field strengths, this formalism can open the door to single-shot THz detection without bandwidth limitations.

Since the use of short-pulse laser excitation on photoconductors and electro-optic crystals in late 1980s’, the development of THz science and technology has been limited to the marginal power level of available lasers with nano-Joule to mJ laser pulse energy. We explore the upper limit of THz wave emitters with the application of the intense lasers (kJ pulse energy and sub-ps pulse duration) at the Laboratory for Laser Energetics at Rochester. In our preliminary experiment in the Laboratory for Laser Energetics, we have used several giant lasers to excite targets and measured THz wave generation during this pilot test. We investigated THz photonics by using unique lasers (from J to kJ pulse energy) originally constructed for laser fusion at the Laboratory for Laser Energetics, Univ. of Rochester. Production of terawatt, joule class THz radiation sources from microchannel targets driven with 100s of joule, picosecond lasers is reported. THz sources of this magnitude are useful for non-linear pumping of matter and for charged particle acceleration and manipulation. Microchannel targets demonstrate increased conversion efficiency compared to planar foil targets, with laser energy to THz energy conversion up to 0.9 percent.

Coherent detection measures both the amplitude and phase of pulsed terahertz (THz) waves simultaneously, forming the foundation for THz time-domain spectroscopy (THz-TDS). This technique has become increasingly prominent in the fields of physics and materials science, allowing researchers to investigate the dynamic properties of various dielectric materials within the 0.1 to 10 THz frequency range, which is previously a challenging spectrum to access. This paper reviews recent advancements and the challenges faced by commonly used coherent detectors in THz-TDS. Our discussion emphasizes the potential for new discoveries in THz photonics and highlights the crucial role of coherent detection in the study of laser-matter interactions.

To create self-controlled radiation photonics systems, it is necessary to have complete information about the nonlinear properties of the materials used. In this Letter, the vibrational mechanism of the giant low-inertia cubic nonlinearity of the refractive index of water in the terahertz (THz) frequency range is experimentally proven. Its dominance, which manifests itself when the temperature of the liquid changes, is demonstrated. The measured nonlinear refractive index in the THz frequency range for a water jet at temperatures from 14°C to 21°C demonstrates a correlation with the theoretical approach, varies in the range 4-10 × 10-10 cm2/W, and is characterized by an inertial time constant of less than 1 ps.

Terahertz (THz) radiation encompasses a wide spectral range within the electromagnetic spectrum that extends from microwaves to the far infrared (100 GHz–∼30 THz). Within its frequency boundaries exist a broad variety of scientific disciplines that have presented, and continue to present, technical challenges to researchers. During the past 50 years, for instance, the demands of the scientific community have substantially evolved and with a need for advanced instrumentation to support radio astronomy, Earth observation, weather forecasting, security imaging, telecommunications, non-destructive device testing and much more. Furthermore, applications have required an emergence of technology from the laboratory environment to production-scale supply and in-the-field deployments ranging from harsh ground-based locations to deep space. In addressing these requirements, the research and development community has advanced related technology and bridged the transition between electronics and photonics that high frequency operation demands. The multidisciplinary nature of THz work was our stimulus for creating the 2017 THz Science and Technology Roadmap (Dhillon et al 2017 J. Phys. D: Appl. Phys. 50 043001). As one might envisage, though, there remains much to explore both scientifically and technically and the field has continued to develop and expand rapidly. It is timely, therefore, to revise our previous roadmap and in this 2023 version we both provide an update on key developments in established technical areas that have important scientific and public benefit, and highlight new and emerging areas that show particular promise. The developments that we describe thus span from fundamental scientific research, such as THz astronomy and the emergent area of THz quantum optics, to highly applied and commercially and societally impactful subjects that include 6G THz communications, medical imaging, and climate monitoring and prediction. Our Roadmap vision draws upon the expertise and perspective of multiple international specialists that together provide an overview of past developments and the likely challenges facing the field of THz science and technology in future decades. The document is written in a form that is accessible to policy makers who wish to gain an overview of the current state of the THz art, and for the non-specialist and curious who wish to understand available technology and challenges. A such, our experts deliver a ‘snapshot’ introduction to the current status of the field and provide suggestions for exciting future technical development directions. Ultimately, we intend the Roadmap to portray the advantages and benefits of the THz domain and to stimulate further exploration of the field in support of scientific research and commercial realisation.

Here, we present our preliminary experimental findings on the generation of broadband terahertz waves from liquid water when subjected to long-wavelength excitation in the range of 1.2 - 1.5 $\mu m$. Our results demonstrate that the THz emission characteristics differ significantly from those observed under 800 nm excitation, as we observe a higher central wavelength and a broader bandwidth of the THz wave emission. Furthermore, a positive correlation between the wavelength for excitation and the THz pulse is measured.

This study experimentally confirms the vibrational nature of giant low-inertia nonlinearity in liquids in the THz range by obtaining temperature dependence of nonlinearity, which correlates with theoretical predictions considering temperature dependent parameters.

We report a systematic investigation into the processes behind a near hundredfold enhanced second harmonic wave generated from a laser-induced air plasma, by examining the temporal dynamics of the frequency conversion processes, and the polarization of the emitted second harmonic beam. Contrary to typical nonlinear optical processes, the enhanced second harmonic generation efficiency is only observed within a sub-picosecond time window and found to be nearly constant across fundamental pulse durations spanning from 0.1 ps to over 2 ps. We further demonstrate that with the adopted orthogonal pump-probe configuration, the polarization of second harmonic field exhibits a complex dependence on the polarization of both input fundamental beams, contrasting with most of the previous experiments with a single-beam geometry.

We report a systematic investigation into the processes behind a near hundred-fold enhanced second harmonic wave generated from a laser-induced air plasma, by examining the temporal dynamics of the frequency conversion processes, and the polarization of the emitted second harmonic beam. Contrary to typical nonlinear optical processes, the enhanced second harmonic generation efficiency is only observed within a sub-picosecond time window and found to be nearly constant across fundamental pulse durations spanning from 0.1 ps to over 2 ps. We further demonstrate that with the adopted orthogonal pump-probe configuration, the polarization of the second harmonic field exhibits a complex dependence on the polarization of both input fundamental beams, contrasting with most of the previous experiments with a single-beam geometry.

Liquid water is a strong absorber in THz range, making the presence of water a nuisance when collecting measurements within this frequency regime. Here, we experimentally demonstrate the generation of broadband THz waves from liquid water with a femtosecond laser. The signal is obtained when a high-intensity laser beam is focused within a water film. This THz signal is distinguished from the signal generated with air plasma by translating the water film across the focal spot. Our observation demonstrates the possibility that liquid water can be a competitive THz source. Our research is also expected to enrich the study of laser-water interactions.

We observe a hundredfold enhanced, directional second harmonic generation as a fundamental beam focuses into a laser-induced air plasma. The enhancement, detectable even with pulses beyond 6 ps, is highlighted among concurrent second harmonic processes.

The concept of Terahertz Field-Induced Second Harmonic (TFISH) Generation is revisited to introduce a single-shot detection scheme based on third order nonlinearities. Focused specifically on the further development of THz plasma-based sources, we begin our research by reimagining the TFISH system to serve as a direct plasma diagnostic. In this work, an optical probe beam is used to mix directly with the strong ponderomotive current associated with laser-induced ionization. A four-wave mixing (FWM) process then generates a strong second-harmonic optical wave because of the mixing of the probe beam with the nonlinear current components oscillating at THz frequencies. The observed conversion efficiency is high enough that for the first time, the TFISH signal appears visible to the human eye. We perform spectral, spatial, and temporal analysis on the detected second-harmonic frequency and show its direct relationship to the nonlinear current. Further, a method to detect incoherent and coherent THz inside plasma filaments is devised using spatio-temporal couplings. The single-shot detection configurations are theoretically described using a combination of expanded FWM models with Kostenbauder and Gaussian Q-matrices. We show that the retrieved temporal traces for THz radiation from single- and two-color laser-induced air-plasma sources match theoretical descriptions very well. High temporal resolution is shown with a detection bandwidth limited only by the spatial extent of the probe laser beam. Large detection bandwidth and temporal characterization is shown for THz radiation confined to under-dense plasma filaments induced by < 100 fs lasers below the relativistic intensity limit.

Two-color laser field-induced plasma filaments are efficient broadband terahertz (THz) sources with intense THz waves emitted mainly in the forward direction, and they have been investigated intensively. However, investigations on the backward emission from such THz sources are rather rare. In this paper, we theoretically and experimentally investigate the backward THz wave radiation from a two-color laser field-induced plasma filament. In theory, a linear dipole array model predicts that the proportion of the backward emitted THz wave decreases with the length of the plasma filament. In our experiment, we obtain the typical waveform and spectrum of the backward THz radiation from a plasma with a length of about 5 mm. The dependence of the peak THz electric field on the pump laser pulse energy indicates that the THz generation processes of the forward and backward THz waves are essentially the same. As the laser pulse energy changes, there is a peak timing shift in the THz waveform, implying a plasma position change caused by the nonlinear-focusing effect. Our demonstration may find applications in THz imaging and remote sensing. This work also contributes to a better understanding of the THz emission process from two-color laser-induced plasma filaments.