Optimizing the performance of a monolithic Tm3+, Ho3+-codoped fiber laser by FBG reflected wavelength and fiber gain matching.

We present the optimization of a 2.1-µm continuous wave monolithic single-oscillator laser by adapting the Fiber Bragg Grating (FBG) reflected wavelength to the maximum gain wavelength of the Tm3+, Ho3+-codoped fiber. Our study examines the power and spectral evolution of the all-fiber laser and demonstrates that matching these two parameters improves the overall performance of the source.

Predicting Laser-Induced Colors of Random Plasmonic Metasurfaces and Optimizing Image Multiplexing Using Deep Learning.

Structural colors of plasmonic metasurfaces have been promised to a strong technological impact thanks to their high brightness, durability, and dichroic properties. However, fabricating metasurfaces whose spatial distribution must be customized at each implementation and over large areas is still a challenge. Since the demonstration of printed image multiplexing on quasi-random plasmonic metasurfaces, laser processing appears as a promising technology to reach the right level of accuracy and versatility. The main limit comes from the absence of physical models to predict the optical properties that can emerge from the laser processing of metasurfaces in which random metallic nanostructures are characterized by their statistical properties. Here, we demonstrate that deep neural networks trained from experimental data can predict the spectra and colors of laser-induced plasmonic metasurfaces in various observation modes. With thousands of experimental data, produced in a rapid and efficient way, the training accuracy is better than the perceptual just noticeable change. This accuracy enables the use of the predicted continuous color charts to find solutions for printing multiplexed images. Our deep learning approach is validated by an experimental demonstration of laser-induced two-image multiplexing. This approach greatly improves the performance of the laser-processing technology for both printing color images and finding optimized parameters for multiplexing. The article also provides a simple mining algorithm for implementing multiplexing with multiple observation modes and colors from any printing technology. This study can improve the optimization of laser processes for high-end applications in security, entertainment, or data storage.

Anti-Counterfeiting White Light Printed Image Multiplexing by Fast Nanosecond Laser Processing.

Passive plasmonic metasurfaces enable image multiplexing by displaying different images when altering the conditions of observation. Under white light, three-image multiplexing with polarization-selective switching has been recently demonstrated using femtosecond-laser-processed random plasmonic metasurfaces. Here, the implementation of image multiplexing is extended, thanks to a color-search algorithm, to various observation modes compatible with naked-eye observation under incoherent white light and to four-image multiplexing under polarized light. The laser-processed random plasmonic metasurfaces enabling image multiplexing exhibit self-organized patterns that can diffract light or induce dichroism through hybridization between the localized surface plasmon resonance of metallic nanoparticles and a lattice resonance. Improved spatial resolution makes the image quality compatible with commercial use in secured documents as well as the processing time and cost thanks to the use of a nanosecond laser. This high-speed and flexible laser process, based on energy-efficient nanoparticle reshaping and self-organization, produces centimeter-scale customized tamper-proof images at low cost, which can serve as overt security features.

Diffraction limited 195-W continuous wave laser emission at 2.09†µm from a Tm3+, Ho3+-codoped single-oscillator monolithic fiber laser.

We present a bi-directionally 793-nm diode-pumped Tm3+, Ho3+-codoped silica polarization maintaining double-clad all-fiber laser based on a single-oscillator architecture emitting 195 W at 2.09 µm in continuous wave mode of operation, with a beam quality near the diffraction limit (M2 = 1.08). The power scaling of the laser is only pump-power-limited in the range of the total available pump power (540 W).

55 W actively Q-switched single oscillator Tm3+, Ho3+-codoped silica polarization maintaining 2.09 µm fiber laser.

A bidirectional 793 nm diode-pumped actively Q-switched Tm3+, Ho3+-codoped silica polarization-maintaining (PM) double-clad (DC) fiber laser is reported. With this fiber laser, 55 W of average output power with 100 ns pulse width at 200 kHz repetition rate and 2.09 µm wavelength is obtained. The pump power injection with end-caps fusion-spliced on fiber tips provides good power stability (< 1.1%) and beam quality factors (M2 < 1.7). The fiber laser output beam polarization factor is 97.5%. At 55 W, no thermal-induced damage is observed on any optical element, and power scaling of the laser is only pump-power-limited in the range of the total available pump power (180 W).

Multiple-path model of spectral reflectance of a dyed fabric.

Experimental results are presented of the spectral reflectance of a dyed fabric as analyzed by a multiple-path model of reflection. The multiple-path model provides simple analytic expressions for reflection and transmission of turbid media by applying the Beer-Lambert law to each path through the medium and summing over all paths, each path weighted by its probability. The path-length probability is determined by a random-walk analysis. The experimental results presented here show excellent agreement with predictions made by the model.

Intracavity changes in the field statistics of Raman fiber lasers.

We present an experiment in which intracavity optical power spectra of a Raman fiber laser are precisely measured both in the forward and in the backward propagation directions near the cavity mirrors. The statistical properties of the intracavity Stokes field are found to be very different before and after reflection on the cavity mirrors. The influence of both the dispersion and the spectral filtering actions of fiber Bragg grating mirrors are discussed.

Influence of dispersion of fiber Bragg grating mirrors on formation of optical power spectrum in Raman fiber lasers.

We show, from experiments and numerical simulations, that dispersion of fiber Bragg grating (FBG) mirrors influences the formation of the optical power spectrum of Raman fiber lasers by shifting the cavity zero-dispersion wavelength inside the FBG reflectivity bandwidth. This results in a spectrum asymmetry, which is well described from a master equation including a third-order dispersion term.