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1. Stable 2 W continuous-wave 261.5 nm laser for cooling and trapping aluminum monochloride

   https://doi.org/10.1364/OE.441741  

   Shaw, J_C; Hannig, S.; McCarron, D_J (October 2021, Optics Express)

   We present a high-power tunable deep-ultraviolet (DUV) laser that uses two consecutive cavity enhanced doubling stages with LBO and CLBO crystals to produce the fourth harmonic of an amplified homebuilt external cavity diode laser. The system generates up to 2.75 W of 261.5 nm laser light with a ∼2 W stable steady-state output power and performs second harmonic generation in a largely unexplored high intensity regime in CLBO for continuous wave DUV light. We use this laser to perform fluorescence spectroscopy on theA¹Π ← X¹Σ⁺transition in a cold, slow beam of AlCl molecules and probe the A¹Π|v′ = 0,J′ = 1〉 state hyperfine structure for future laser cooling and trapping experiments. This work demonstrates that the production of tunable, watt-level DUV lasers is becoming routine for a variety of wavelength-specific applications in atomic, molecular and optical physics. 

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2. Translucent Si Solar Cells Patterned with Pulsed Ultraviolet Laser Beam

   https://doi.org/10.1002/aesr.202400147  

   Chowdhury, Ashif_H; Yoon, Heayoung_P (September 2024, Advanced Energy and Sustainability Research)

   We report an application of a pulsed ultraviolet (UV) laser (λ = 355 nm) in producing translucent Si solar cells. This process efficiently generates a densely packed microhole array on a fully fabricated Si P‐N junction solar cell in just a few minutes. Herein, prototype cells with a nominal microhole diameter of 23 μm with a spacing between 60 and 300 μm are fabricated. High‐resolution electron‐beam microscopy reveals that the UV laser beam introduces amorphized silicon oxide (SiO_x) in proximity to the patterned microholes via localized heating in air. Quantitative photovoltaic (PV) analysis shows a decline in the open‐circuit voltage (V_oc) and the fill factor (FF) of the cells with the increase in the microhole density, likely due to the P‐N junction damage during the laser beam irradiation. Despite the reduction inV_ocand FF, the solar cells retain a short‐circuit current density (J_sc) above 90% without post‐processing. The inherent microhole geometry associated with the laser beam profile allows multiple light scattering within the confined microhole structure, enhancing the translucency of the cells. While further development is required for optimization, these findings support the potential use of UV laser beams for fast and scalable production of translucent solar cells. 

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3. How Do the Purcell Factor, the Q ‐Factor, and the Beta Factor Affect the Laser Threshold?

   https://doi.org/10.1002/lpor.202000250  

   Khurgin, Jacob B.; Noginov, Mikhail A. (February 2021, Laser & Photonics Reviews)

   Abstract As lasers get more and more miniaturized and their dimensions become comparable to the wavelength, two interconnected phenomena take place: the fraction of spontaneous radiation going into a specific laser mode (β‐factor) increases and can ultimately reach unity, while the radiative lifetime gets shortened by the Purcell factorF_p. Often it is assumed that an increase of these two factors, along with the quality factor (Q‐factor), almost invariably causes reduction of the lasing threshold. This assumption is tested on various photonic and plasmonic lasers, demonstrating that, while there is obvious correlation between the aforementioned factors and the laser threshold, the dependence is far from being straightforward and omnipresent. Depending on specific laser material and geometry, the threshold can decrease, increase, or stay unchanged whenβ‐factor,Q‐factor, andF_pincrease. For the most part, the reduction of threshold is achieved simply by reducing the laser volume and this volume reduction can concurrently cause the increase inβ‐factor and/or Purcell factor, but it would be imprudent to say that the increase in either of these factors is the cause of the threshold reduction. 

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4. Ultrafast laser stress generation landscape in fused silica

   https://doi.org/10.1364/OE.561444  

   Laverty, Kevin_A; Chalifoux, Brandon_D (June 2025, Optics Express)

   Although stress is a critical factor in many ultrafast laser-based fabrication techniques, its relationship to different laser operating parameters remains poorly understood. Here, we investigate the stress landscape within fused silica generated by ultrafast laser pulses, with repetition rates of 100???900?kHzand pulse energies of 200???4000?nJ, by measuring all three components of the stress-induced curvature change of fused silica plates. We find that for all repetition rates, there is an inflection in the stress when the average laser power is about 60?mW, and this inflection is not correlated with the morphological transition from nanogratings to melting, as observed from cross-section imaging. The equibiaxial and antibiaxial components of stress exhibit a characteristic average ratio of about ?1.65 up until the visually observed onset of melting within the modifications, which occurs when the average laser power is about 423?mW. We conclude that nanogratings produce a characteristic stress state, with a maximum magnitude that is reached at lower pulse energy than nanograting erasure. Beyond nanograting erasure, the stress state is more variable and distinct from the nanograting-induced stress state. 

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5. Dynamic counterpropagating all-normal dispersion (DCANDi) fiber laser

   https://doi.org/10.1364/PRJ.528873  

   Prakash, Neeraj; Musgrave, Jonathan; Li, Bowen; Huang, Shu-Wei (August 2024, Photonics Research)

   The fiber single-cavity dual-comb laser (SCDCL) is an emerging light-source architecture that opens up the possibility for low-complexity dual-comb pump-probe measurements. However, the fundamental trade-off between measurement speed and time resolution remains a hurdle for the widespread use of fiber SCDCLs in dual-comb pump-probe measurements. In this paper, we break this fundamental trade-off by devising an all-optical dynamic repetition rate difference (Δf_rep) modulation technique. We demonstrate the dynamic Δf_repmodulation in a modified version of the recently developed counterpropagating all-normal dispersion (CANDi) fiber laser. We verify that our all-optical dynamic Δf_repmodulation technique does not introduce excessive relative timing jitter. In addition, the dynamic modulation mechanism is studied and validated both theoretically and experimentally. As a proof-of-principle experiment, we apply this so-called dynamic CANDi (DCANDi) fiber laser to measure the relaxation time of a semiconductor saturable absorber mirror, achieving a measurement speed and duty cycle enhancement factor of 143. DCANDi fiber laser is a promising light source for low-complexity, high-speed, high-sensitivity ultrafast dual-comb pump-probe measurements. 

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