Abstract Terahertz (THz) radiation within atmospheric transmission window regions has attracted significant interest owing to its low atmospheric attenuation and potential for long-distance applications. However, the development of high energy and efficient THz laser operating in these frequency regions remains challenging. In this study, we present a high energy pulsed CH 3 F gas THz laser operating at an atmospheric transmission window near 1.3 THz (231 μ m) based on an L-shaped resonant cavity pumped by a multi-transverse-mode TEA CO 2 laser. The generated THz radiation was systematically investigated in terms of emission wavelength, output characteristics, pulse temporal waveform, and laser beam quality. The emission wavelength was determined to be 231 μ m using a scanning Fabry–Perot interferometer. At a pump energy of 1.3 J, a maximum THz pulse energy of 20.2 mJ was obtained under an optimum gas pressure of 1300 Pa, corresponding to a photon conversion efficiency of 38.9%. At the highest output energy, the THz pulse duration was approximately 110 ns, corresponding to a peak power of approximately 184 kW, and the measured beam quality factor was M 2 = 2.09.
The influence of dispersion on the dynamics of pulses propagating in air in the mid-infrared range is investigated analytically. The dynamics are analyzed for both normal and anomalous group velocity dispersion. The pulse parameters are shown to be described by an asymptotic series, whose terms decrease up to a certain order and then diverge. A criterion is derived that determines the maximum number of terms that may be retained in the dispersion expansion. An explicit analytical expression for the pulse duration dynamics, including dispersion terms up to seventh order, is derived. It is shown that air humidity can significantly affect pulse propagation.
Abstract This paper investigates the modulation characteristics and drive circuit design of LiNbO 3 phase modulators in coherent free-space optical communication systems. The goal is to enhance modulation accuracy and reduce bit error rate (BER). A high-gain broadband drive circuit based on the OP27G chip is proposed to improve system stability. Theoretical and experimental results show that the optimal performance occurs when the drive voltage is slightly below the half-wave voltage, minimizing signal distortion and BER. This approach outperforms traditional methods, improving both signal quality and system stability. Future research may explore advanced modulation formats and machine learning techniques.
Abstract We theoretically investigate the intra-band optical absorption in GaAs spherical quantum dots (QDs) confined by a screened Kratzer potential. The energy levels and wave functions are obtained analytically within the adopted approximation using the Nikiforov–Uvarov method, and the optical absorption coefficient is evaluated from Fermi’s golden rule. The results show that increasing the characteristic confinement length r 0 produces a redshift and reduces the absorption intensity. In contrast, increasing the potential depth V 0 leads to a systematic blueshift with a non-monotonic variation of the peak intensity. Increasing temperature mainly suppresses the absorption intensity through the Fermi–Dirac occupation factors, while the resonance energy remains nearly unchanged. These results demonstrate that screened Kratzer confinement provides an effective mechanism for tuning the intra-band optical response of GaAs QDs.
Abstract Under microsecond-level short-time observation, FMCW LiDAR beat-frequency estimation is limited by coarse FFT frequency spacing and sparse spectral sampling, leading to unstable peak localization and degraded ranging accuracy. To address this problem without extending the observation window, this work formulates beat-frequency extraction as a sub-bin peak localization problem. Three methods are investigated: three-point parabolic interpolation on the logarithmic magnitude spectrum (M1), weighted multi-point quadratic fitting around the spectral peak (M2), and time-domain maximum-likelihood matching (M3). Their performance is evaluated through Monte Carlo simulations and experimentally validated on a coherent FMCW LiDAR platform using a 5 m fiber-delay target. Experimental results show that, for a 1 μ s observation window, sub-bin localization significantly reduces the error fluctuation compared with direct FFT, with the standard deviation decreasing from 7.24 mm to 2.66 mm using M3. When the observation window is extended to 10 μ s, the improved spectral sampling further compresses the error distribution; M2 achieves a median ranging error of 0.99 mm, while M3 gives the lowest standard deviation of 0.97 mm. These results demonstrate that sub-bin peak localization can effectively improve ranging accuracy and stability under short-time FMCW LiDAR measurement conditions.
