Laser sources operating near a wavelength of four microns are important for a broad range of applications that require power scaling beyond the state-of-the-art. The highest power demonstrated in the spectral region from a solid-state laser source is based upon nonlinear optical (NLO) conversion using the NLO crystal ZnGeP2 (ZGP). High-power operation in ZGP is known to be limited by thermal lensing. By comparing the figure of merit for thermal lensing in ZGP with other NLO crystal candidates, CdSiP2 (CSP) particularly offers significant advantages. However as was the case with ZGP during its early development, the physics of observed crystal defects, and their relevance to power scaling, was not at first sufficiently understood to improve the crystal’s characteristics as a NLO wavelength conversion element. During the past decade, significant progress has been made (1) with the first reported growth of a large CSP crystals, (2) in understanding the crystal’s characteristics and its native defects, (3) in improving growth and processing techniques for producing large, low-loss crystals, and (4) in demonstrating CSP’s potential for generating high-power mid-infrared laser light. The paper will summarize this progress.
Over the last decade it has been demonstrated that nonlinear optical (NLO) crystals can be grown by laser precipitation in customized glasses and used for electro-optic applications. It has been further demonstrated that this novel crystal growth technique is capable of fabricating nonlinear waveguide structures, where the polar axis of the crystal is aligned along the growth direction. Femtosecond precipitation of NLO crystals in glass has the potential to be a low-cost method of creating functional optical elements. In order to realize this goal, the orientation of the NLO crystals must be carefully controlled. In the present study, a widely used electro-optical crystal, Lithium Niobate, was precipitated in 33LiO2-33Nb2O5-34SiO2 (mol%) (LNS) glass, forming NLO crystalline structures in an amorphous matrix. Glass fabrication techniques for making high quality glass, and the crystallization parameter space were explored to determine the optimal conditions for smooth and continuous crystal growth. The crystalline orientation of the precipitated lithium niobate was determined for a variety of writing conditions, and the growth technique was extended to multi-dimensional structures.
Optical processes that rely on second-order nonlinear optical effects such as second harmonic generation and
optical parametric amplification require the use of non-centrosymmetric crystals (NCCs). Recently it has been
reported that femtosecond lasers can be used to precipitate NCCs within supersaturated glasses, forming
waveguide structures . During laser writing, a combination of thermal gradients together with the laser
polarization, cause the alignment of the polar axis of the NCC along the writing direction. Femtosecond
precipitation of NCCs in glass has the potential to be a lower-cost alternative to other methods of achieving NCC
waveguiding structures. In this study a widely used ferroelectric NCC, Lithium Niobate, was precipitated in
33LiO2-33Nb2O5-34SiO2 (mol%) (LNS) glass, forming crystalline aligned channels within the amorphous glassy
matrix. The precipitated lithium niobate was characterized and the structural orientation determined. The
waveguiding characteristics were measured for several conditions to determine optimal power and writing speed.
This procedure was then modified to optimize the precipitated 1-D structures for photonic and holographic
Photorefractive (PR) hybrid liquid crystal (LC) cells have combined the space-charge field generated in either a
polymer (using e.g. PVK;C60) with the large birefringence from a LC layer to generate PR grating for beam
coupling applications. The efficiency of PR beam coupling in hybrid devices is dependent on the amplitude of
the space-charge field, as well as the ability of the LC molecules to align with the corresponding field. In this
paper the time dynamics of the formation of the PR gratings are measured in LC hybrid systems and are used to
explain the large variation of gain coefficients found in the literature.
The complexity of photorefractive polymers arises from multiple contributions to the photo-induced index grating. Analysis of the time dynamics of the two-beam coupling signal is used to extract information about the charge species responsible for the grating formation. It has been shown in a commonly used photorefractive polymer at moderate applied electric fields, the primary charge carriers (holes) establish an initial grating which, however, are followed by a subsequent competing grating (electrons) that decreases the two-beam coupling efficiency. We show by upon using higher applied bias fields, gain enhancement can be achieved by eliminating the electron grating contribution and returning to hole gratings only.
Modern table-top laser systems are capable of generating ultrashort optical pulses with sufficiently high intensity to induce nonlinear optical effects in many of the materials that are used in the construction of optical components. We discuss the interaction of such pulses with three types of dielectric filters: (a) dielectric stacks composed of a sequence of two dielectric layers with quarterwave optical thickness, (b) idealized rugate filters, i.e., filters with a refractive index profile that is sinusoidally modulated on the length scale of an optical wavelength, and (c) a rugate filter composed of two materials. We present finite difference time-domain (FDTD) computer simulations of optical pulse propagation through dielectric filters for pulses with widths in the range 5 to 100 fs and with peak intensities up to 10 TW/cm2. At low intensities the reflective properties of the dielectric filters determined using FDTD simulations are directly comparable to the results calculated using the characteristic matrix method, while at high intensities optical nonlinearity in the dielectric layers is responsible for a decrease in the reflectance of the filter and causes stretching and distortion of the reflected pulses.
Modern table-top laser systems are capable of generating ultrashort optical pulses with sufficiently high intensity to induce nonlinear optical effects in many of the materials that are used in the construction of optical components. In this paper we discuss the interaction of such pulses with two types of dielectric filters: (a) dielectric stacks composed of a sequence of two dielectric layers with quarter-wave optical thickness and (b) rugate filters, i.e. filters with a refractive index profile that is sinusoidally modulated on the length scale of an optical wavelength.
Our simulations were performed using the finite difference time domain (FDTD) technique to numerically integrate the Maxwell curl equations for both the electric and magnetic fields. This technique enables the reflection of an optical pulse from a multilayer dielectric stack to be accurately simulated and also allows the incorporation of dispersion and nonlinearity through an auxiliary differential equation.
We present computer simulations of optical pulse propagation through dielectric filters for pulses with pulsewidths in the range 5-100 fs with peak intensities up to ~10 TW/cm2. At low intensities the reflective properties of the dielectric filters determined using FDTD simulations are directly comparable to the results calculated using the characteristic matrix method, while at high intensities, optical nonlinearity in the dielectric layers is responsible for a decrease in the reflectance of the filter and causes stretching and distortion of the reflected pulses.