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Laser-Induced Dynamic Gratings

A novel optical arrangement for heterodyne detection of laser-induced gratings based on the use of a phase mask for both excitation and probe beams provides phase stability and control without the need for an active stabilization scheme. The arrangement greatly simplifies the laser-induced grating experiment. The performance of the technique in both transmission and reflection geometries is illustrated through measurements of bulk and surface acoustic waves generated by picosecond laser pulses.

Laser-Induced Dynamic Gratings

Over time, the laser-induced grating decays due to carrier recombination (electronic decay with the rate of τR) and carrier diffusion (spatial decay with the rate of τD). The diffusion term depends on the transient grating period: fine gratings diffuse faster than coarser ones. Accordingly, if we measure the temporal behavior of the diffracted signal over a series of different periods Λ, we can determine the carrier diffusion coefficient D [2].

nanoGe Fall Meeting (NFM) is a multiple symposia conference celebrated yearly and focused on a broad set of topics of advanced materials preparation, their fundamental properties, and their applications, in fields such as renewable energy, photovoltaics, lighting, semiconductor quantum dots, 2-D materials synthesis, charge carriers dynamics, microscopy and spectroscopy semiconductors fundamentals, etc.

where λpump is the pump wavelength and θpump is the angle of intersection of the two pump beams. The probe beam, which can be a single beam or two beams in a heterodyne configuration, is Bragg scattered off of this transient grating and collected with a photodiode. Bragg scattering of a beam of light off of a transient grating, formed by standing wave interference in a material from another light beam, was first observed experimentally in 1967 by Boersch and Eichler [35]. A detailed compilation of theoretical and experimental work on dynamic gratings can be found in Ref. [36]. In our setup, we use an approach [37] which uses a phase mask image which is refocused on the sample as seen in Fig. 1.

Chaotic Brillouin dynamic gratings (BDGs) have special advantages such as the creation of single, permanent and localized BDG. However, the periodic signals induced by conventional optical feedback (COF) in chaotic semiconductor lasers can lead to the generation of spurious BDGs, which will limit the application of chaotic BDGs. In this paper, filtered optical feedback (FOF) is proposed to eliminate spurious BDGs. By controlling the spectral width of the optical filter and its detuning from the laser frequency, semiconductor lasers with FOF operate in the suppression region of the time-delay signature, and chaotic outputs serving as pump waves are then utilized to generate the chaotic BDG in a polarization maintaining fiber. Through comparative analysis of the COF and FOF schemes, it has been demonstrated that spurious BDGs are effectively eliminated and that the reflection characterization of the chaotic BDG is improved. The influence of FOF on the reflection and gain spectra of the chaotic BDG is analyzed as well.

Brillouin dynamic gratings (BDGs) have attracted increasing and extensive attention due to their applications in distributed fiber sensing1, tunable optical delays2, all-optical flip-flops3, all-optical signal processing4, and high-resolution optical spectrometers5. A BDG is generated by the stimulated Brillouin scattering (SBS) interaction between two counter-propagating pump waves in optical fibers. Since the first proof of concept experiment on the BDG in a polarization maintaining fiber (PMF) was reported in 20086, BDGs have been successfully generated in single mode fibers7,8, few-mode fibers9, photonic crystal fibers10 and integrated chips11. Meanwhile, the spectral characteristics of BDGs in PMFs have been analyzed in detail12,13. In addition, different types of BDGs have been proposed and realized including, for example, phase-shifted BDGs14, chirped BDGs15 and sampled BDGs16.

Electromagnetically induced grating (EIG) is an optical interference phenomenon where an interference pattern is used to build a dynamic spatial diffraction grating in matter. EIGs are dynamically created by light interference on optically resonant materials and rely on population inversion and/or optical coherence properties of the material. They were first demonstrated with population gratings on atoms.[1] EIGs can be used for purposes of atomic/molecular velocimetry,[2] to probe the material optical properties such as coherence and population life-times,[3] and switching and routing of light.[4][5] Related but different effects are thermally induced gratings and photolithography gratings.

The writing lasers form a grating by modulating density of matter or by localizing matter (trapping) on the regions of maxima (or minima) of the writing interference fields. A thermal grating is an example. Matter gratings have slow dynamics (milliseconds) compared to population and phase gratings (potentially nanoseconds and faster).

Abstract:Long dynamic population gratings (DPGs) formed in rare-earth-doped fibers have unique spectral characteristics compared to other types of fiber gratings, making them suitable for controlling the spectral composition of lasers. Depending on the type, length, and position of the DPGs in the cavities of lasers, they can be used for various purposes, ranging from the stabilization of single-frequency radiation to regular wavelength self-sweeping (WLSS) operation. Lasers based on DPGs are sources of narrow-band radiation with a fixed or sweeping generation spectrum. One of the main advantages of such lasers is the simplicity of their design, since they do not require special spectral elements or drivers for spectrum control. In this paper, we review the research progress on fiber lasers based on DPGs. The basic working principles of different types of DPGs will be introduced in the theoretical section. The operation of lasers based on absorption and gain DPGs and their practical applications will be discussed and summarized in experimental section. Finally, the main challenges for the development of such lasers will be presented.Keywords: population grating; self-sweeping; fiber lasers; rare-earth; saturable absorber; single-frequency radiation; spatial hole burning; long fiber gratings

Multilayer dielectric (MLD) gratings with high diffraction efficiency and a high laser-induced damage (LID) threshold for pulse compressors are key to scaling the peak and average power of chirped pulse amplification lasers. However, surface defects introduced by manufacturing, storage, and handling processes can reduce the LID resistance of MLD gratings and impact the laser output. The underlying mechanisms of such defect-initiated LID remain unclear, especially in the femtosecond regime. In this Letter, we model dynamic processes in interactions of a 20-fs near-infrared (NIR) laser pulse and a MLD grating design in the presence of cylindrically symmetrical nodules and particle contaminants and cracks at the surface. Utilizing a dynamic model based on a 2D finite difference in time domain (FDTD) field solver coupled with photoionization, electron collision, and refractive index modification, we study the simulation results for the damage site distribution initiated by defects of various types and sizes and its impact on the LID threshold of the grating design.

We present the first operation of a distributed feedback solid state dye laser with a dynamic, pump-induced grating. Broadly tunable, narrow band operation in the region of 616 nm (604-649 nm) has been demonstrated with perylene red laser dye doped in poly(methyl methacrylate) (PMMA), when pumped with a frequency doubled Nd:YAG laser. Conversion efficiencies of 20%, corresponding to 35% optical-to-optical efficiency, have been measured. The laser bandwidth was between 0.01 and 0.04 nm, and smooth tuning over more than 200 GHz has been demonstrated. 041b061a72


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