Applied Physics B最新文献

The modulation of laser pulse with high photon energies is an important tool for the observation and control of the dynamic of inner-shell electron in atoms and nucleon in atomic nuclear. We present a theoretical method for the reshaping of extreme ultraviolet (XUV) pulses by the modulation of an infrared (IR) pulse combining with the propagation effects of the XUV pulse in helium. The spectrum is redistributed within a specific frequency range around the coherent frequency of the atomic system, which allows for frequency tuning and spectral compression of the XUV pulse, significantly enhancing its radiative intensity at different frequencies. These findings deepen our understanding of the propagation effect and control mechanisms of XUV pulses in atomic media.

This paper proposes a novel square-core optical fiber with an internally gold-coated structure for RI sensing. This novel design offers a wide area for the analyte channel and a flat surface for gold film deposition. Additionally, the unique structure facilitates enhanced field interaction with the gold film, as the metal film is positioned along the core surface. The proposed sensor demonstrates outstanding performance not only in RI sensing but also in cancer cell and pathogen identification. The recorded sensitivities are 25,000 nm/RIU for RI sensing in the range of 1.33–1.41, 8571.43 nm/RIU for cancer cell detection, and 6382.98 nm/RIU for pathogen identification in water. Other performance parameters such as the figure of merit (FOM), sensor resolution, and detection accuracy (DA) also highlight the potential of this sensor in the respective domain. Another contribution of this work is the incorporation of a machine learning approach, called Gaussian Process Regression (GPR), to predict the resonance wavelength for any intermediate RI value, which could broaden the scope of this sensor’s applications.

This paper offers a novel semiconductor metamaterial structure capable of supporting sluggish, dispersionless plasmonic waves. The suggested arrangement demonstrates the slow light phenomena, which is an important aspect of photonic crystals. Incorporating semiconductor ellipsoidal nanowires into the metamaterial structure adds a degree of freedom in order to engineer the propagation of slow light surface plasmon polaritons. Numerical simulations confirm the excited wave’s plasmonicity.

In this study, the spatial coherence of the 46.9 nm capillary discharge extreme ultraviolet (EUV) laser was analyzed. The fringe visibility of the laser was measured using Young’s double-slit method at different transverse positions of the laser spot and showed the same trend as the laser intensity spatial distribution. Additionally, the fringe visibilities corresponding to different Ar pressures were measured and were found to increase with the laser intensities. The results also showed that the relative intensity and maximum fringe visibility of the laser were linearly reduced with a decrease in capillary length from 35 cm to 25 cm. The highest fringe visibility value reached 0.935 under the conditions of a 35 cm capillary length and an internal Ar pressure of 20 Pa. These findings contribute to the expansion of applications for the 46.9 nm lasers.

In this work, hafnium diselenide (HfSe₂)-based saturable absorbers (SA) were fabricated and applied for the modulation of Tm:YAP lasers. In continuous-wave mode, a 12.9 W laser diode was used to pump the Tm:YAP crystal, resulting in an output power of 2.35 W at 1996.2 nm, corresponding to an optical-to-optical conversion efficiency of 19%. In passively Q-switched mode, the Tm:YAP laser modulated by the HfSe₂ SA achieved an average output power of 1.45 W, with a pulse width of 712.8 ns and a pulse repetition frequency of 103.17 kHz at a central wavelength of 1989.1 nm. The corresponding optical-to-optical conversion efficiency was 11.2%, with a single-pulse energy of 14.1 µJ and a peak power of 19.7 W. The rate equation was used to calculate the modulation depth (10%), saturation flux (1 kJ/cm²), and unsaturated loss (0.0505).

We report on a compact, passively Q-switched waveguide laser fabricated via femtosecond direct laser writing (fs-DLW) in an Yb:LuGG crystal. Prior to Q-switching experiments, continuous-wave operation was systematically characterized under various cavity configurations, achieving a maximum output power of 678 mW and a slope efficiency of 53.6% using a 70% output coupler. Passive Q-switching was implemented by incorporating single-walled carbon nanotubes (SWCNTs) as a saturable absorber, enabling stable laser operation over several hours. The 7.39-mm-long waveguide laser operated near 1030 nm, and its Q-switched performance was investigated using three output couplers with different transmissions. The best performance was obtained with a 50% output coupler, yielding pulses as short as 35 ns, a maximum output power of 478 mW, and a highest repetition rate of 2.51 MHz. These results demonstrate the excellent compatibility between fs-DLW-fabricated Yb:LuGG waveguides and SWCNT-based saturable absorbers, offering a promising route toward robust and highly efficient compact pulsed laser sources.

To achieve high-peak-power and highly-stable pulsed laser output at 1112 nm, a birefringent filter (BF) and a Brewster window (BW) were incorporated into an 808 nm laser-diode (LD) side-pumped Nd: YAG cavity. This configuration provides triple functions of polarization control, frequency selection, and spectral filtering, effectively suppressing competing oscillations at the 1116 nm and 1123 nm lines while reducing the number of longitudinal modes at 1112 nm. Furthermore, a pre-biased transversely pressurized electro-optic Q-switching technology was employed to lower the modulation voltage of the MgO: LN crystal, thereby enhancing its extinction efficiency. At a maximum LD pump current of 100 A, an average output power of 2.386 W, a pulse width of 4.82 ns, and a peak power of 4.950 MW were measured from the 1112 nm pulsed laser with a pulse repetition frequency of 100 Hz. The corresponding pulse-to-pulse fluctuation of single-pulse energy and pulse width were ± 0.30% and ± 0.84%, respectively. At 1.0 kHz, the average power, pulse width, and peak power measured 11.389 W, 6.22 ns, and 1.831 MW, respectively, while the power and temporal fluctuation remained low at ± 0.72% and ± 1.77%. These results demonstrate that the proposed technique, which combines pre-biased pressurized MgO: LN electro-optic Q-switching with BW and BF filtering, offers a viable approach to enhancing both the peak power and stability of 1112 nm pulsed lasers.

Fractional-order vortex beams (FO-VBs) exhibit complex phase structures, distinct from their integer-order counterparts, particularly featuring gap discontinuities and rich dynamics during propagation. However, high-resolution measurement of their actual phase evolution remains a challenge. This study introduces a compact, improved single-element heterodyne interferometer designed for precise, direct measurement of the wavefront phase of FO-VBs in free space. Our setup successfully captured the intricate phase distribution within the radial dark region, revealing that it comprises a series of vortex–antivortex pairs with opposite topological charges. Theoretical and experimental results demonstrate that as the fractional part of the topological charge increases, the phase fluctuation region from a single pair expands. Upon approaching an integer charge, these pairs annihilate head-to-tail, culminating in a complete 2π phase jump and the formation of a new primary vortex. Concurrently, beam quality degrades from integer to half-integer order, reaching its minimum at the latter, which aligns with the variation trend of the phase distribution, demonstrating an intrinsic link between beam quality and phase structure. This robust interferometric method, with the capability for phase distribution reconstruction even under obstructed conditions, provides critical insights into the phase dynamics of FO-VBs and is anticipated to be a valuable tool for predicting beam quality evolution and interaction effects in complex media, such as atmospheric turbulence.

The characterisation technique of asynchronous cross-correlation that uses a known auxiliary reference laser to measure the duration of unknown ultrashort test laser pulses has been improved by adding a delayed copy of the reference laser pulse, creating a known time reference for autocalibration. The calibrated delay is formed by partially inserting a thin optical plate into the reference beam. This modified technique, which provides significantly higher precision than the standard asynchronous cross-correlation technique, was used to measure the duration of ultrafast pulses in the ultraviolet region at a wavelength unsuited to the use of common autocorrelation techniques. The split-beam principle can also be extended to include spectral characterisation of ultrashort pulses.

Values of all four elements of the cubic susceptibility in KDP and DKDP (80% deuteration) crystals at wavelengths of 1030 and 515 nm were measured for the first time by the modified z-scan technique. Values of the tensor elements (chi _{11}), (chi _{16}), and (chi _{33}) are approximately the same for the considered crystals. The value of the effective cubic susceptibility in the DKDP ((Z-)cut) crystal does not depend on the azimuthal angle of rotation in contrast of KDP crystal at the experimental measurement accuracy. Thus the values of tensor elements (chi _{18}) are different in both crystals.