We demonstrate an all-fiber passively Q-switched Yb-doped laser using a piece of Sm-doped fiber as a saturable absorber. The laser was pumped by two 25W, 975 nm fiber coupled diodes and Q-switching was initiated when the ASE generated in the core of the gain fiber bleached the Sm-doped saturable absorber. The laser produced 1064 nm pulses with 28 μJ pulse energy and a 200 ns pulse width at a repetition rate of 100 kHz. The pulse energy and peak power are an order of magnitude higher than what previous reported which was also in all-fiber configuration. Effects of laser parameters, such as Sm-fiber length, pump power and duration on laser performance were presented and discussed. Stable Q-switched pulses were obtained at the repetition rate varying from 10 kHz to 100 kHz, which makes this laser suitable for different applications.
Real-time depth metrology during material removal via laser ablation is useful in many forms of laser machining. Until now, coaxial optical coherence tomography (OCT) metrology was achieved by the coupling of an OCT imaging beam and ablating beams using a dichroic filter. We present an alternative design with all fiber delivery that is more suitable for surgical laser ablation applications. The novel system design integrates a high peak-power pulsed Yb-doped fiber laser (1064nm) coupled directly into the sample arm of a swept-source OCT system (λ c = 1310nm). We measured the OCT signal degradation due to dispersion and attenuation through the ablation fiber laser cavity. Ablation progression is measured in real-time using M-mode OCT. The mean depth targeting error was found to range from 10µm to 80µm in phantom ablation experiments and 21µm to 60µm in bone ablation. A number of issues have been solved, including point-spread function (PSF) peak broadening due to signal delay and dispersion, high bending loss due to dissimilar fiber used throughout the design, and problems due to the extremely high ablation power to swept-source power ratio (> 2x10 4 peak to average power). To our knowledge, this is the first demonstration of thermal-mediated laser ablation drilling integrated with coaxial OCT imaging through a single-mode, single-cladded output fiber, without using dichroic beam splitters or free-space optic filters anywhere in the optical path and with this high ablation laser power to OCT source power ratio. The removal of bulk optics compared to existing designs opens a new path for compact integration of the entire system. Also, since the ablation laser and OCT feedback system exist along the same fiber path, the need for maintenance and repair are greatly reduced since spatial beam alignment and the potential open-air contamination of optical surfaces are virtually eliminated. We believe that this integrated system is a great candidate for adoption in depth-controlled surgical ablation applications.
This study presents the design of a system used to monitor laser ablation in real-time using Optical Coherence Tomography (OCT). The design of the system involves a high-powered fiber laser (wavelength of 1064nm, 1kW peak power) being built directly into the sample arm of the OCT system (center wavelength 1310). It is shown that the OCT laser light and subsequent backscatter pass relatively unaffected through the fiber laser. Initial results are presented showing monitoring of the ablation process at a single point in real time using m-mode imaging.
We demonstrated a passively Q-switched Yb-doped fiber laser in an all-fiber configuration that used a piece of a Yb-doped fiber with a smaller core than the gain fiber as a saturable absorber. The laser generated stable output pulses at 1064 nm with a narrow line width of less than 0.2 nm. The Q-switched pulses have a pulse width of 140 ns and pulse energy of 141 J at a repetition rate of 100 kHz. The peak power of $1 kW and high slope efficiency of 51% were obtained. The repetition rate of this laser can be varied from a few kHz to 100 kHz with a potential of reaching up to 250 kHz. Stimulated Raman scattering was observed, though at 70 dB below the laser emission. The estimated stimulated Raman threshold is 6.2 kW, which allows this laser to further scale up the power. Because of its high peak power and adequate average power, the laser can be used as a stand-alone module for some applications in material processing. It can be also used as a seed laser for further power amplification.
As important components of air pollutant, volatile organic compounds (VOCs) can cause great harm to environment and human body. The concentration change of VOCs should be focused on in real-time environment monitoring system. In order to solve the problem of wavelength redundancy in full spectrum partial least squares (PLS) modeling for VOCs concentration analysis, a new method based on improved interval PLS (iPLS) integrated with Monte-Carlo sampling, called iPLS-MC method, was proposed to select optimal characteristic wavelengths of VOCs spectra. This method uses iPLS modeling to preselect the characteristic wavebands of the spectra and generates random wavelength combinations from the selected wavebands by Monte-Carlo sampling. The wavelength combination with the best prediction result in regression model is selected as the characteristic wavelengths of the spectrum. Di®erent wavelength selection methods were built, respectively, on Fourier transform infrared (FTIR) spectra of ethylene and ethanol gas at di®erent concentrations obtained in the laboratory. When the interval number of iPLS model is set to 30 and the Monte-Carlo sampling runs 1000 times, the characteristic wavelengths selected by iPLS-MC method can reduce from 8916 to 10, which occupies only 0.22% of the full spectrum wavelengths. While the RMSECV and correlation coe±cient (Rc) for ethylene are 0.2977 and 0.9999 ppm, and those for ethanol gas are 0.2977 ppm and 0.9999. The experimental results show that the iPLS-MC method can select the optimal characteristic wavelengths of VOCs FTIR spectra stably and e®ectively, and the prediction performance of the regression model can be signi¯cantly improved and simpli¯ed by using characteristic wavelengths.
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