Signal beam

About: Signal beam is a research topic. Over the lifetime, 1881 publications have been published within this topic receiving 20717 citations.

Relative intensity noise transfer of large-bandwidth pump lasers in Raman fiber amplifiers

Abstract: A theoretical analysis of the Raman amplification in optical fibers and the pump-to-signal relative intensity noise (RIN) transfer has been performed in the spectral domain. An efficient Raman amplification of a monochromatic signal beam by a large-bandwidth pump beam has been demonstrated for a pump bandwidth much smaller than the Raman linewidth. Under the same approximation the pump-to-signal RIN transfer has been calculated in both cases of copropagating and counterpropagating beams in the two limiting cases of modulated monochromatic and smooth-profile large-bandwidth pump beams. At low frequencies the excess of noise evidenced in the case of a modulated monochromatic pump beam did not exist in the case of large-bandwidth pseudoincoherent sources. As this noise reduction can be as large as 13 dB for a 40 dB net gain of the amplifier, such incoherent pumping sources must be considered for the purpose of low-noise Raman amplifiers.

High-resolution laser spectroscopy based on polarisation-modulated optical phase conjugation in a demountable cathode discharge

Abstract: Doppler-free laser spectroscopy based on polarisation-modulated optical phase conjugation in a demountable hollow-cathode discharge is a sensitive analytical method, as a visible coherent laser beam is generated as the signal. Because the conjugate signal beam is a time-reversed replica of the probe beam, the optical signal can be detected conveniently and efficiently. Spectral resolution is excellent as both Doppler and Lorentzian broadenings are negligible. Taking advantage of the polarisation properties of the phase-conjugate wavefront, we demonstrate a novel polarisation-modulated detection scheme in this spectroscopic method using a relatively low-power continuous-wave laser and the hyperfine structure of the sodium 3s 2S1/2 to 3p 2P3/2 transition. Some advantages of the polarisation-modulated degenerate four-wave mixing are discussed.

Optical amplification in Ho3+-doped transparent oxyfluoride glass ceramics at 750nm

Abstract: Positive transient optical gain has been demonstrated in Ho3+-doped transparent oxyfluoride glass-ceramics. A pump and probe experiment has been designed to show this result. High power laser pulses at 532nm were used as the pump source to strongly populate the Ho3+S25:F45 level due to nonresonant ground state absorption. Low power cw laser radiation at 750nm was used as the probe beam. The signal beam stimulates the emission associated with the Ho3+S25:F45→I75 electronic transition at 750nm. In addition to this, the high power pump pulses provide population inversion between the S25:F45 and I75, initial and final states of the transition, respectively, giving rise to the optical amplification of the signal beam. A gain coefficient of 3.7cm−1 (∼16dB∕cm) was obtained for a pump energy density of about 135mJ∕cm2 and a signal beam power density of 6μW∕cm2.

Surface condition measuring method and measuring device, polishing machine, and semiconductor device manufacturing method

Abstract: PROBLEM TO BE SOLVED: To provide an optical measuring method, a measuring device, and a polishing machine capable of measuring a polishing end point or the remaining film thickness rapidly, easily and accurately by comparing a signal waveform with a reference value even if the signal waveform, has noise, variation of the signal waveform to the wavelength is gentle, or variation in the signal waveform is extremely minute and fine around the polishing end point. SOLUTION: This measuring method measures the surface condition of the substrate surface based on the extent of agreement of the signal waveform obtained from a reflected signal beam or a transmission signal beam by irradiating beams on the substrate surface with the reference waveform. The signal waveform is a spectral waveform after noise elimination or standardization, the reference waveform is one or more spectral waveforms obtained by other measurement or calculation, and the extent of agreement is calculated using cross correlation.

Spatial-Polarization-Independent Parametric Up-Conversion of Vectorially Structured Light

Abstract: Spatial-polarization-independent (SPI) parametric conversion is the basis of many optical applications, such as SPI frequency interfaces for communication channels carried by vector modes and up-conversion detection for polarization-resolved imaging. However, realizing such conversion remains a challenge. In the proof-of-principle study presented here, we demonstrate SPI parametric up-conversion using a polarization Sagnac nonlinear interferometer based on type-II second-harmonic generation. Our results show that the vector profile (including both polarization and intensity) and associated spin-orbit-coupling state of the vector signal beam can be transferred to the frequency-doubled beam with high fidelity. The principle lays the foundation for a SPI frequency interface for quantum and classical channels based on vector modes and also paves the way for up-conversion detection of polarization-resolved images in the mid- and far-infrared regions.