Applied Physics B最新文献

An apodized Long Period Grating (LPG) is presented to compute and depict the temperature sensitivity for different resonant wavelengths in the transmission spectrum. The spectrum often gets distorted due to overlapping of multiple modes and appearance of large quantity side lobes as a result of the impacts of higher order period. Therefore, the introduction of apodization profile is necessary to obtain the proper shape of the spectrum by preventing any distortions. It has been noted that the higher order mode (LP₀₇) shows greater temperature sensitivity with 0.043 nm/^o C as compared with the lower order modes (i.e., LP₀₄, LP₀₅, LP₀₆) for 100–600° C. Different Machine Learning models are implemented for the predictive analysis of resonant wavelength changes in accordance with the temperature effects for enhancing the effectiveness of the sensor response. This approach is highly desirable in various applications by ensuring the safety, efficiency and reliability of the LPG-based sensing outcomes.

A He-free CO₂ laser excited by a longitudinal pulsed discharge produced short laser pulses at repetition rates up to 700 Hz. A discharge tube with an inner diameter of 8 to 16 mm and a length of 60 to 80 cm was employed, with a fast, high-voltage pulse of approximately 22.0 to 30.3 kV and a rise time of 300 ns. No pre-ionization or fast gas flow systems were used. The oscillation characteristics at various repetition rates, gas mixing ratios, gas pressures, input energies, output coupler reflectivities and discharge tube sizes were investigated. A short laser pulse with a tail was produced under all conditions. In the discharge tube with an inner diameter of 8 mm and a length of 80 cm, a CO₂/N₂ mixture at a ratio of 1:2 and a wavelength of 10.6 μm, the maximum laser output energies were 32.5, 13.1 and 3.27 mJ at repetition rates of 300, 500 and 700 Hz, respectively.

The detection of chiral molecules is highly important for drug safety; however, the chiral signals of chiral drugs are weak and are concentrated mainly in the ultraviolet band, and it is difficult for traditional methods to achieve precise detection. In this work, we apply a high-precision detection method for chiral molecules based on optical weak value amplification (WVA) in the ultraviolet band. By integrating WVA with ultraviolet spectrum analysis, we obtain the distribution of the intensity contrast ratio in the ultraviolet band, revealing the spectrum of the chiral signals. We demonstrate the application of this approach by detecting the optical rotatory dispersion (ORD) and circular dichroism (CD) of artemisinin with a high precision of 10^–6 rad, surpassing traditional detection methods. This work contributes to the precise detection of chiral spectra in the ultraviolet band and the recognition of chiral drugs, which is important in the pharmaceutical field.

A novel, absorption lineshape-based, laser-induced fluorescence diagnostic has been developed for simultaneous, single-point measurements of temperature, pressure, and velocity in high-enthalpy flow environments. The technique uses wavelength-tuned, narrow-linewidth, continuous-wave lasers to excite atomic potassium vapor, which is used as a flow tracer. The laser pumps the potassium D2 electronic transition, near 766.7 nm, while fluorescence from both the D1 and D2 lines is monitored simultaneously. The technique uses spectral lineshape and line position for inferring flow field properties, eliminating the need for detailed, setup-dependent calibration factors for quantitative measurements. The technique was tested and validated in argon and nitrogen in a shock tube with temperatures, pressures, and velocities ranging from 1000-2600 K, 0.1(-)0.7 atm, and 650-1200 m/s. Measurement volumes and uncertainties were as low as 3.5 (hbox {mm}^3) and 5%, respectively, and measurement rates were up to 100 kHz. Accurate understanding of temperature, pressure, and velocity enables a more complete characterization of a compressible flow system as other quantities, including mass flux, Mach number, thrust, and stagnation conditions, can be calculated.

The laser-induced damage threshold of a grating waveguide output coupler (GWOC) exposed to laser radiation at a wavelength of 1030 nm and with a pulse duration of 500 fs was investigated. The GWOC is a combination of a sub-wavelength circular grating and a partial reflector based on a Nb₂O₅ and SiO₂ multilayer sequence. It was designed to be used as an output coupler of a thin-disk laser cavity for the generation of beams with radial polarization. The results revealed a laser-induced damage threshold (LIDT) fluence of 0.36 J/cm² for single-pulse tests and 0.26 J/cm² for multiple-pulse conditions with up to 1000 shots. These threshold values are comparable to those of an unstructured output coupler with Nb₂O₅ and SiO₂ coating layers, highlighting the minor influence of the grating on the LIDT.

In this work we present the development and characterization of a high-gain, double-pass and four-pass femtosecond Yb: KYW amplifier pumped by two polarization-coupled tapered laser diodes emitting a total power of 9 W at 979 nm. The amplifier utilized relies on a crossed-crystals configuration, employing two 3-mm-long 10%-at. doped N_g-cut Yb: KYW crystals with orthogonal orientation of the respective N_m-axis in order to optimize pump absorption and minimize gain narrowing. The amplifier was seeded either with almost Fourier-transform limited ∼300-fs pulses from an in-house-made Yb: KYW oscillator, or with 5-ps-long, chirped pulses (∼15 nm full-width at half-maximum bandwidth around 1030 nm) from a commercial Yb-doped fiber laser. In both cases, we achieved a four-pass small-signal gain G₀ > 100 and an optical-to-optical extraction efficiency of about 30%, even at low seed average power levels. The amplifier showed excellent spatial beam quality preservation up to the full pump power (M² < 1.1) and good preservation of the pulse duration with negligible gain narrowing in case of the 300-fs bulk seeder and pulses (:le:)200 fs after compression in case of the fiber laser seeder.

The propagation of light through opaque materials, served by periodic arrays of subwavelength holes, has revolutionized imaging and sensor technology with a breakthrough of extraordinary optical transmission (EOT). The enhanced optical transmission assisted by surface plasmon resonances (SPR) has become the most ingenious phenomenon in the field of light-matter interaction. Active tuning of SPR presents a new and simple way to control spectral features of the EOT signal (without the need to change the geometrical structure of the device). This provides a new possibility to integrate an active EOT device with tunable operational frequencies on a single chip of photonic integrated circuits (PIC)- a new scalable instrument in the optoelectronic industry, and quantum technology for improving subwavelength optical imaging and biomedical sensing. In this review, we discuss the fundamentals of EOT, the role of SPR, and how the active quantum plasmonic control of the EOT device makes it a feasible on-chip electro-optic programmable element for integrated photonics.

A waveguide-based optical parametric oscillator for coherent Raman scattering applications is presented, exploiting four-wave mixing in a silicon nitride waveguide. Benefiting from its long propagation length of 20 mm in combination with a narrowband pump laser, idler pulses with an energy of up to 210 pJ and a spectral bandwidth down to 11.2 (hbox {cm}^{-1}) were obtained. By combining these narrowband idler pulses and the residual pump pulses, coherent Raman spectroscopy and microscopy were possible with a signal-to-noise ratio of up to 13.4. Thus, the presented compact and stable waveguide-based light source paves the way towards integrated lab-on-a-chip coherent Raman applications.

We have developed a highly sensitive fiber optic sensor that can measure temperature and pressure. The sensor comprises two Fabry–Perot interferometers (FPIs), FPI₁ and FPI₂, connected in parallel. FPI₁ is composed of single mode fiber (SMF)—capillary—SMF spliced together, with a ventilation hole on the capillary. FPI₂ is composed of SMF—capillary—SMF, and the capillary is filled with polyimide (PI). It is found that FPI₁ is almost insensitive to temperature, but sensitive to air pressure. FPI₂ is sensitive to temperature, but not sensitive to pressure. When the free spectra range (FSR) of FPI₁ and FPI₂ approaches twice the relationship, they are connected in parallel to form a first-order harmonic vernier effect (HVE). When the HVE sensor is used for air pressure sensing, FPI₁ is the sensing cavity and FPI₂ is the reference cavity. When the HVE sensor is used for temperature sensing, FPI₂ is the sensing cavity and FPI₁ is the reference cavity. The experimental results showed that the sensitivities of the pressure and temperature of the HVE sensor are 76.71 nm/MPa and 113.29 nm/ °C, respectively. This is currently the highest temperature sensitivity reported in literature. The accuracy of the obtained intersection point in HVE sensor is higher and than that of that of traditional Vernier effect. In addition, the FSR relationship required to form HVE is easier to achieve. By utilizing the temperature and air pressure sensitivities of FPI₁ or FPI₂, as well as that of the HVE sensor, a sensitivity measurement matrix can be formed to achieve simultaneous measurement of temperature and air pressure.

Surface nanoscale axial photonics (SNAP) microcavities exhibit a regular transmission spectrum and encompass multiple axial modes, making them highly relevant for precise and wide-range displacement sensing applications. However, conventional SNAP microcavity shapes, such as parabolic and Gaussian curves, demonstrate limitations in handling noise interference from external environments, compromising displacement sensing accuracy. In this study, we propose a robust displacement sensing approach based on the bat-shaped SNAP microcavity. This unique profile supports a uniform first-order axial field mode. By utilizing the first-order axial mode as a reference, we apply Resonance Spectra Normalization (RSN) to standardize the resonance spectrum, reducing the impact of external perturbations. Extensive simulations validate the effectiveness of this technique. When coupling parameters deviate by up to 8%, our sensing method achieves a prediction error confined within a 4 μm range, compared to 14 μm in conventional displacement sensing solutions. This advancement enhances the sensor’s immunity to environmental noise, potentially revolutionizing microcavity displacement sensing, particularly in challenging environments beyond controlled cleanrooms.