Showing papers on "Signal beam published in 2023"
06 Mar 2023
TL;DR: In this article , the effects of interference competition in heterodyne demodulation systems were analyzed and it was shown that interference competition depends on the signal amplitude, the interferometric light intensity ratio and the relative phase difference.
Abstract: The Laser Doppler Vibrometry (LDV) system can measure parameters such as amplitude, velocity and acceleration of micro-vibrating objects. However, in the actual measurement process, in addition to the probe beam and the reference beam, as the surface roughness of the measured object increases and the diffuse reflectance decreases, the echo energy of the laser will decrease rapidly. This phenomenon can be extended to heterodyne detection systems. Due to the limitation of optical devices, the third beam (ie stray beam) caused by parasitic reflection is unavoidable. At the same time, the third beam has a certain intensity and phase distribution, which seriously affects signal demodulation of micro-vibrating objects. This paper analyzes the effects of multi-beam interference competition in heterodyne demodulation systems. Mathematical analysis shows that the interference competition depends on the signal amplitude, the interferometric light intensity ratio and the relative phase difference. Through mathematical derivation and simulation verification, the following conclusions can be drawn: when the relative phase difference is π rad, when the ratio of light intensity between the probe light and the stray light is controlled to tend to one, the simple harmonic motion with an amplitude of 1 nm is demodulated, and the amplitude can be observed to be nearly 200 times of the enhancement effect. For micro vibration with different amplitudes, the simulation shows that when the amplitude coefficient is π, the demodulation amplitude does not have amplification effect, and the amplitude coefficient is π can be used as the limit of demodulation amplitude amplification. This method has great application value in the high-sensitivity measurement direction of micro-vibrating objects.
TL;DR: In this paper , an intracavity parametric signal amplification system for improving the sensitivity of a gravitational-wave detector at high frequencies was developed to aim at an observation of a postmerger remnant of a binary neutron star collision.
Abstract: This article summarizes our study to develop an intracavity parametric signal amplification system for improving the sensitivity of a gravitational-wave detector at high frequencies to aim at an observation of a postmerger remnant of a binary neutron star collision. The detector configuration is based on a dual recycling interferometer and an optical parametric amplifier crystal is inserted into the signal recycling cavity. The cavity is detuned and an optical spring is generated for the differential motion of the two end mirrors. The amplifier converts the energy of the pump beam to the optical spring and the spring frequency can be enhanced to a few kilohertz. The system is contrasting to the squeeze injection technique commonly used in second-generation gravitational-wave detectors. Although both techniques use an optical parametric amplifier crystal, the squeeze injection reduces noise while signal amplification increases the signal to modify the optomechanical dynamics of the system.
TL;DR: In this article , a pump-enhanced optical parametric oscillator (OPO) at 3.8 µm was demonstrated, which was pumped by a 1064 µm fiber laser with a linewidth of 18 kHz.
Abstract: A high efficiency, continuous-wave, narrow linewidth, pump-enhanced optical parametric oscillator (OPO) at 3.8 µm was demonstrated, which was pumped by a 1064 nm fiber laser with a linewidth of 18 kHz. The low frequency modulation locking technique was employed to stabilize the output power. The wavelengths of signal and idler were 1475.5 nm and 3819.9 nm at 25 °C, respectively. The pump-enhanced structure was applied, leading to a maximum quantum efficiency of over 60% with pump power of 3 W. The maximum output power of idler light is 1.8 W with a linewidth of 363 kHz. The excellent tuning performance of the OPO was also demonstrated. In order to avoid mode-splitting and decrease of pump enhancing factor due to feedback light in the cavity, the crystal was placed obliquely to the pump beam and the maximum output power was increased by 19%. At the maximum output power of idler light, the M2 factors in the x and y directions were 1.30 and 1.33, respectively.
29 Mar 2023
TL;DR: In this paper , the transverse coherence length of the idler field is investigated in the context of parametric down conversion, where a nonlinear crystal is pumped by a laser and spontaneous emission takes place in signal and idler modes according to the phase matching conditions.
Abstract: In parametric down conversion, a nonlinear crystal is pumped by a laser and spontaneous emission takes place in signal and idler modes according to the phase matching conditions. A seed laser can stimulate the emission in the signal beam if there is mode overlap between them. This also enhances the emission in the idler beam, affecting its coherence properties. While the degree of coherence of the idler field as a function of the seed power has already been studied, the transverse coherence length has not yet been properly investigated. The transverse coherence length is a key parameter of optical beams that determines the beam divergence, for example. Here, we present a theoretical and experimental investigation of the transverse coherence length in stimulated down conversion. In addition, we make a connection between stimulated down conversion and partially coherent sources like the Gaussian Schell model beams, and show that in general the idler field cannot be described with this model.
TL;DR: In this paper , a single-beam method based on the third-order nonlinear-ellipse rotation (NER) measurement in thick samples was proposed to determine the pulse properties, including the duration and linear chirp.
Abstract: We present a single-beam method based on the third-order nonlinear-ellipse-rotation (NER) measurement in thick samples to determine the pulse properties, including the duration and linear chirp. Our approach exploits the influence of the intrinsic second-order dispersions of the nonlinear materials, which affect the NER signal as a function of propagation. Two advantages can be highlighted: no delay line is required, and there are no phase-matching issues. To test our method, we characterized ultrafast chirped pulses from a Ti:sapphire amplified laser system and tunable pulses from an optical parametric amplifier using two samples with high dispersions and nonlinearities: SF6 and LaSF-N30 optical glasses.
24 Jan 2023
TL;DR: In this paper , the authors apply the concept of intensity interferometry to holography by combining a signal beam with a reference and measuring their intensity cross-correlations using a time-tagging single-photon camera.
Abstract: As first demonstrated by Hanbury Brown and Twiss, it is possible to observe interference between independent light sources by measuring correlations in their intensities rather than their amplitudes. In this work, we apply this concept of intensity interferometry to holography. We combine a signal beam with a reference and measure their intensity cross-correlations using a time-tagging single-photon camera. These correlations reveal an interference pattern from which we reconstruct the signal wavefront in both intensity and phase. We demonstrate the principle with classical and quantum light, including a single photon. Since the signal and reference do not need to be phase-stable, this technique can be used to generate holograms of self-luminous or remote objects using a local reference, thus opening the door to new holography applications.
TL;DR: In this article , the concept of all-optical beam switching in graded-index multimode optical fibers is introduced and experimentally demonstrated, and a simple geometrical representation of the beam switching operation is proposed, whose validity is quantitatively confirmed by the experimental mode decomposition of the output beam.
Abstract: We introduce and experimentally demonstrate the concept of all-optical beam switching in graded-index multimode optical fibers. Nonlinear coupling between orthogonally polarized seed and signal beams permits to control the spatial beam quality at the fiber output. Remarkably, we show that even a weak few-mode control beam may substantially enhance the quality of an intense, highly multimode signal beam. We propose a simple geometrical representation of the beam switching operation, whose validity is quantitatively confirmed by the experimental mode decomposition of the output beam. All-optical switching of multimode beams may find important applications in high-power beam delivery and fiber lasers.
TL;DR: In this article , a reflective configuration for the single-beam SERF comagnetometer was proposed, where the laser light simultaneously used for optical pumping and signal extraction is designed to pass through the atomic ensemble twice.
Abstract: The single-beam comagnetometer working in the spin-exchange relaxation-free (SERF) state is being developed into a miniaturized atomic sensor with extremely high precision in rotation measurement. In this paper, we propose a reflective configuration for the single-beam SERF comagnetometer. The laser light simultaneously used for optical pumping and signal extraction is designed to pass through the atomic ensemble twice. In the optical system, we propose a structure composed of a polarizing beam splitter and a quarter-wave plate. With this, the reflected light beam can be separated entirely from the forward propagating one and realize a complete light collection with a photodiode, making the least light power loss. In our reflective scheme, the length of interaction between light and atoms is extended, and because the power of the DC light component is attenuated, the photodiode can work in a more sensitive range and has a better photoelectric conversion coefficient. Compared with the single-pass scheme, our reflective configuration has a stronger output signal and performs better signal-to-noise ratio and rotation sensitivity. Our work has an important impact on developing miniaturized atomic sensors for rotation measurement in the future.