KEYWORDS: Nanoparticles, Particles, Temperature metrology, Optical engineering, Laser scattering, Laser interferometry, Laser applications, Signal to noise ratio, Signal detection, Scanning electron microscopy
As a well-known noncontact optical sensing technique, laser self-mixing interferometry (SMI) exhibits outstanding merits of low-cost, self-alignment, compactness, and high sensitivity, and it has been applied to typical geometrical quantity measurements, tomography, object imaging, as well as nanoparticle sizing. In SMI nanoparticle detection, as a result of Brownian motion, laser beam stochastically interacts with each particle in the illuminating volume, producing self-mixed signals with Lorentz shape power spectra, whose spectral broadening width is directly related with particle sizes. In general, FFT is always the first choice to obtain signals’ power spectra, but due to the influence of spectrum leakage, the heights of spectral lines may rise or fall and then change original Lorentz shapes and further increase sizing errors. Here, an all phase FFT (apFFT) method has been proposed to greatly suppress spectrum leakage, correct spectral line heights and further improve nanoparticle sizing errors for Rayleigh scattering cases. The apFFT method proposed is advantageous to developing precise SMI particle sensors or instruments, which may be applicable to chemical or medical applications.
A multiple mode rate equations model of the dual-cavity solid-state vortex laser has been established and used to investigate the dynamic process of the Laguerre-Gaussian (LG) modes competition. We calculated the dynamic processes of the modes LG01, LG02 and LG03. The results show that the laser exhibits a complex cross-spiking and cross-relaxation characteristic during the early stage of mode competition. The later start of a mode would cause the cross-spiking and cross-relaxation process, and ultimately the mode started firstly may even not be the one that can be sustained at steady state. To ensure the successful mode selection, the reflectivity of the secondary cavity should be larger than that of the primary cavity, but a too large one would decrease the stable output power of the mode LG01, even to its suppression. The pumping beam distribution has a great influence on the dynamic process and the stable output power of the modes, so the radius and the order of the pumping beam should be optimized. In our case, the optimized beam radius is 0.4 mm, slightly larger than the beam radius of the mode LG00, i.e.0.3 mm, and the optimized order is 4. Moreover, if the laser do not have proper reflectivities of output couplers and pumping beam distribution, the mode selection may not be demonstrated only by optimization of the aperture radius, which would only delay the crossspiking.
The parameter C, named optical feedback strength coefficient, has always exhibited significance in the field of laser self-mixing interferometry (SMI), and it can be utilized to assess the feedback regime or reconstruct an external target's motion. Plenty of researchers have concerned about the technique of acquiring C from SMI signals. Instead of empirical conclusions and according to clear mathematical deduction, this manuscript proposes a fast and cost-efficient method to evaluate C, eliminating large calculation consumption as in the reported optimization methods. Regardless of laser types and the line-width enhancement factor α, it is possible to achieve a relative precision within 5% for C ranging from 0.1 to 5, which is helpful for SMI theoretical studies and SMI sensors.
A novel optical accelerometer based on laser self-mixing effect is presented and experimentally demonstrated, which
consists of a mass-loaded elastic-beam assembly and laser self-mixing interferometer. Under external acceleration, an
inertial force is applied to the mass, flexible beams deflect from their equilibrium position. The deflection can be read
out by the self-mixing interferometer. In order to reduce the impact of higher harmonic, wavelet analysis is introduced to
remove singular points. Preliminary results indicate that the resolution is 0.19μg/Hz1/2 within a bandwidth of 100Hz. The
optical accelerometer has the potential to achieve high-precision, compact accelerometers.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.