Denise M Krol

• University of California, Davis

The light–energy coupling during femtosecond laser processing of glass is mediated by non-linear ionization mechanisms through the formation of an electron plasma. Its transient optical properties provide information about the density, temperature and scattering rate of the excited electrons. In turn, these properties strongly condition the feature...

We investigate the interaction of ultrashort laser pulses with ternary zinc phosphate glasses. We explore the viability of ten different glass compositions with different levels of alumina to inscribe optical waveguides via the fs-laser direct writing technique, finding that only samples with [O]/[P] ratios of 3.25 are suitable candidates. We also...

We have investigated the effect of the laser wavelength on the fabrication of optical waveguides and tracks of modified material via direct laser writing inside fused silica. The size of the laserinscribed tracks, the material modification thresholds, the structural changes, and the waveguide writing energy range show a strong dependence on laser w...

We have investigated the permanent refractive index changes inside fused silica glass after laser inscription of waveguides using ultrashort laser pulses at different wavelengths. To this end the laser frequency was detuned using an optical parametric amplifier (OPA) combined with a confocal arrangement (for cleaning the laser Gaussian spatial prof...

Nonlinear processing of glass using femtosecond laser pulses has been shown as a reliable method for producing photonic devices. To optimize the writing of optical waveguides and harness the true power of fs-laser modification, it is imperative that we gain a greater understanding of the physical mechanisms behind it. This requires experimental and...

The electronic structure of warm dense silicon dioxide has been investigated by x-ray absorption near-edge spectroscopy. An ultrafast optical laser pulse was used to isochorically heat a thin silicon dioxide sample, and measured spectra were compared with simulations generated by molecular dynamics and density functional theory. In comparison with...

The fs-laser induced refractive index change in zinc aluminum phosphate glasses and its underneath structural modifications have been investigated both at the surface and in bulk.

Zinc-phosphate glass surface ablation was investigated using tightly focused fs-laser pulses. Evidences of self-scattering effects due to the interaction between the laser light and a transient plasma-generated during surface ablation have been investigated.

We present a numerical model that describes the propagation of a single femtosecond laser pulse in a medium of which the optical properties dynamically change within the duration of the pulse. We use a finite-difference time-domain method to solve the Maxwell’s equations coupled to equations describing the changes in the material properties. We use...

We present a numerical model which describes the propagation of a single femtosecond laser pulse in a medium of which the optical properties dynamically change within the duration of the pulse. We use a Finite Difference Time Domain (FDTD) method to solve the Maxwell's equations coupled to equations describing the changes in the material properties...

The permanent refractive index change induced by ultrashort laser pulses in zinc phosphate glasses has been investigated both at the surface and in bulk. At the sample surface, irradiations have been performed by using loosely focused single fs-laser pulses at different energies. Optical microscopy images of the irradiations illustrate an interfero...

We experimentally investigate the self-reflectivity of intense strongly focused femtosecond laser pulses used for single-shot femtosecond laser ablation of silicon-on-insulator (SOI). We model the self-reflectivity using 2D finite-difference time-domain simulations of a single femtosecond laser pulse interacting with a submicrometer-sized time- and...

Good quality waveguides can be fabricated in zinc phosphate glasses with O/P ratios of 3.25 using the femtosecond-laser writing technique. Compositional effects, including the addition of Al2O3 and rare-earth doping, are discussed as well as results on the fabrication of active devices.

We report measurement of the ablation depth and self-reflectivity from thin silicon films illuminated by a single tightly focused femtosecond laser pulse. We show the dependence of ablation depth on incident laser pulse fluence can be modeled with a transfer-matrix method, taking into account transient reflectivity and light propagation in a strati...

Femtosecond (fs)-laser processing of CdSxSe1-x-doped borosilicate glasses was investigated to create hybrid multiscale structures consisting of semiconductor nanocrystals embedded in microscopic domains defined by the laser irradiation. Laser processing was carried out with both low (1 KHz) and high (1 MHz) repetition rate fs-lasers using pulse flu...

Optically tunable mesoscale structures offer unparalleled potential for photonic device applications. Here, we report the creation of composite photonic structures consisting of CdSxSe1−x quantum dots (QDs) customized within lines, first written in a glass by femtosecond laser pulses. CdSxSe1−x-doped borosilicate glasses were pulsed with a fs-laser...

We have investigated the thermal stability of femtosecond laser modification inside fused silica. Raman and FL spectroscopy show that fs-laser induced non-bridging oxygen hole center (NBOHC) defects completely disappear at 300 °C, whereas changes in Si-O ring structures only anneal out after heat treatment at 800-900 °C. After annealing at 900 °C o...

The creation of fiber Bragg gratings (FBGs) in optical fibers by laser irradiation causes the formation of defects in the modified glass. We have used confocal fluorescence spectroscopy to identify the location and types of defects formed after writing FBGs with the femtosecond laser phase mask technique. Our results show that non-bridging oxygen h...

Femtosecond laser processing of a CdSxSe1−x doped borosilicate glass by a 1 kHz femtosecond laser with pulse energies up to 100 μJ gave rise to smooth altered micron-size regions within the glass. The fs-laser exposed glass formed nanocrystals when heat treated above the glass transition temperature. The fluorescence intensities in the non-resonant...

We have investigated waveguide writing in Er-Yb doped zinc polyphosphate glass using a femtosecond laser with a repetition rate of 1 KHz. We find that fabrication of good waveguides requires a glass composition with an O/P ratio of 3.25. The dependence on laser writing parameters including laser fluence, focusing conditions, and scan speed is repor...

We have investigated the direct fabrication of subsurface waveguide amplifiers in Er-Yb zinc polyphosphate glass by utilizing the relationship between the initial glass composition and the resulting changes to the network structure after modification by fs laser pulses. Waveguides, exhibiting internal gain of 1 dB / cm at 1.53 μm when pumped with 5...

Submicron single-shot ablation features produced by femtosecond laser pulses was investigated in silicon-on insulator with atomic force microscopy. The results are fitted with a model that includes secondary absorption in the laser-induced plasma.

Focused femtosecond laser pulses from a 1 MHz fiber laser were used to create modifications in Er- Yb doped zinc phosphate glass. Two glasses with similar phosphate glass networks but different network modifiers were investigated. To understand the resulting changes caused by the femtosecond laser pulses various characterization techniques were emp...

Since the first experiments on femtosecond laser waveguide writing the question on which mechanisms are responsible for the refractive index change immediately arose. Several efforts have been made in that direction but no conclusive answer has been achieved yet. In fact, it has been observed that several factors determine the actual mechanism domi...

We report a surface morphology study on single-shot submicron features fabricated on silicon on insulator by tightly focused femtosecond laser pulses. In the regime just below single-shot ablation threshold nano-tips are formed, whereas in the regime just above single-shot ablation threshold, a saturation in the ablation depth is found. We attribut...

We have studied the relationship between the initial glass composition and the structural changes associated with laser-induced refractive index modification in a series of Er-Yb doped and undoped zinc phosphate glasses. White light microscopy and waveguide experiments are used together with Raman and fluorescence spectroscopy to characterize the s...

We report the relationship between the initial glass composition and the resulting microstructural changes after direct femtosecond laser waveguide writing with a 1 kHz repetition rate Ti:sapphire laser system. A zinc polyphosphate glass composition with an oxygen to phosphorus ratio of 3.25 has demonstrated positive refractive index changes induce...

Femtosecond laser writing was used to fabricate waveguides in undoped and rare-earth doped polyphosphate glasses. The influence of glass composition and laser parameters on waveguide properties and structural changes in the glass will be discussed.

This study describes the fabrication of hybrid micro-and nanostructures of semiconductor nanocrystals arranged in microscopic lines inside of a borosilicate glass doped with CdS x Se 1-x . This was performed using a two step process of (1) ultrafast laser modification and (2) heat treatment. The glass was photomodified using focused sub-picosecond...

Laser tweezers Raman spectroscopy (LTRS) was used to acquire the Raman spectra of leukemic T lymphocytes exposed to the chemotherapy drug doxorubicin at different time points over 72 hours. Changes observed in the Raman spectra were dependent on drug exposure time and concentration. The sequence of spectral changes includes an intensity increase in...

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Recent advances in the application of glassy materials in planar and fiber-based photonic structures have led to novel devices and components that go beyond the original thinking of the use of glass in the 1960s, when glass fibers were developed for low-loss, optical communication applications. Exploitation of the material's compositional flexibili...

Laser tweezers Raman spectroscopy (LTRS) was used to characterize the Raman fingerprints of the metabolic states of Escherichia coli (E. coli) cells and to determine the spectral changes associated with cellular response to the antibiotic Cefazolin. The Raman spectra of E. coli cells sampled at different time points in the bacterial growth curve ex...

Laser tweezers Raman spectroscopy was used to detect the cellular response of Escherichia coli cells to penicillin G-streptomycin and cefazolin. Time-dependent intensity changes of several Raman peaks at 729, 1,245, and 1,660 cm−1 enabled untreated cells and cells treated with the different antibiotic drugs to be distinguished.

We report the analysis of the vibrational modes of intranuclear protein inclusions isolated from the brain of human subjects with the Fragile X-associated tremor/ataxia syndrome (FXTAS). In this preliminary study, Raman spectra of optically trapped inclusions were measured and analysed to determine protein composition and structure. Our main findin...

Changes to the glass network structure after modification with tightly focused 1043 nm , 400 fs laser pulses have been studied in Er–Yb doped phosphate glass using in situ confocal Raman microscopy. For femtosecond laser writing conditions that result in heat accumulation, the 710 and 1209 cm ^-1 Raman peaks, which are due to the ( P O P...

Changes to the glass structure after femtosecond laser modification have been studied in multiple metaphosphate glass systems using white light and laser microscopy. Results indicate initial glass structure is important to the resulting morphological changes.

We have studied thermal annealing of fs-laser fabricated waveguides in fused silica using confocal fluorescence and Raman microscopy. The results show that laser-induced NBOHC defects disappear at much lower temperatures than three-membered SiO rings.

We have investigated the microscopic origins of the induced χ⁽²⁾ in two phosphate glasses: a self-prepared lanthanum phosphate glass with molar composition 0.2 La ₂ O ₃ 0.8 P ₂ O ₅ and a commercial sodium alumino phosphate glass (IOG-1, Schott Glass Technologies, Inc.) with molar composition 0....

We have studied thermal poling in lanthanum phosphate glasses with molar composition 0.2La2O30.8P2O5. A χ(2) can be induced for poling voltages above 3kV and temperatures above 300°C. The induced χ(2) profile consists of a single layer with a width of 30μm near the anodic surface. The magnitude of the induced χ(2) is 0.88pm/V. The results, which ar...

We have systematically studied femtosecond-laser fabrication of optical waveguides in an Er-Yb doped phosphate glass. Waveguides were written using the IMRA America FCPA muJewel D-400 femtosecond fiber laser system with pulse repetition rates ranging from 250 kHz to 2.2 MHz. At every pulse repetition rate a series of waveguides was written while va...

Tight focusing of ultrashort (∼100 fs) infrared laser pulses of moderate energy (typically 1–10 μJ) into a glass results in very high, localized (in space and time) intensities, in excess of 1014 W/cm2. Under these conditions the laser–materials interaction becomes highly nonlinear, resulting in permanent modification of the material. By precisely...

Structural changes associated with femtosecond laser fabrication of waveguides and Bragg gratings in fused silica were analyzed using optical microscopy and laser spectroscopy. Using 800 nm femtosecond lasers with a kilohertz repetition rate and various pulse energies, both smooth and rough modifications were induced. The different modification reg...

Waveguides were written in fused silica using both a femtosecond fiber laser with a 1 MHz pulse repetition rate and a femtosecond amplified Ti:sapphire laser with a 1 kHz repetition rate. Confocal Raman and fluorescence microscopies were used to study structural changes in the waveguides written with both systems. A broad fluorescence band, centere...

Luminescence properties of Cr3+ ions in a silica-based precursor glass, and in fabricated optically transparent glass-based nanocrystalline composites, have been investigated. The luminescence spectra of the precursor glass revealed a wide range of crystal fields and showed the 4T2–4A2 broadband emission of Cr3+ ions in a weak crystal field, combin...

Waveguides were fabricated in fused silica using kHz and MHz repetition rate femtosecond lasers. Raman and fluorescence microscopy showed increases in 3-membered rings for both cases and fewer NBOHC-defects when writing with the MHz laser.

F− ions enter silica gels as Si-F bonds and free and hydrogen-bonded HF. During drying, heating, and sintering, all HF is removed, and a significant portion of the structural fluoride (Si-F) is also eliminated through reaction with Si—OH, which results in formation of siloxane bonds. Substitution of Si-Cl bonds for Si—OH bonds assists in retention...

The precipitation and growth of copper nanoparticles in an optically transparent aluminosilicate glass matrix was investigated. The size of particles in this heterophase glass-based composite was modified in a controlled manner by isothermal heat treatments. A multitechnique approach, consisting of Raman scattering spectroscopy, high-resolution tra...

We have investigated the optical properties of Cr3+ ions in an alkali gallium silicate glass system and in two glass-based nanocomposites with nucleated β-Ga2O3 nanocrystals. The nucleation and growth of the nanocrystalline phase in the host glass matrix were monitored by Raman scattering spectroscopy and angle-dispersive x-ray diffraction. A broad...

Three-dimensional, faceted assemblies of CdSe nanocrystals were grown to microscopic sizes sufficient for identification and direct characterization. Analyses made by optical, fluorescence, and transmission electron microscopy showed that individual, faceted superlattices are composed of nearly single-size nanocrystals assembled into fcc lattices....

Confocal fluorescence microscopy was performed on gratings generated in all-silica core optical fiber with an ultrafast infrared laser and a phase mask. Upon excitation with 488 nm light a broad fluorescence centered at 650 nm is observed. The fluorescence intensity varies periodically with a 4.5 μm pitch, in reasonable agreement with the 4.284 μm...

Waveguides were written in soda lime silicate glasses with a composition of xNa2O xCaO (1-2x)SiO2, where x = 15 and 20, using an amplified femtosecond laser. The waveguides formed around, not inside the exposed regions. This is similar to the waveguide behavior our group first observed in a phosphate glass, Schott IOG-1, and is distinctly different...

Consider the interaction between visible or near-infrared laser light with a ``transparent'' material, such as glass. Under normal conditions, i.e continuous low power illumination, the glass will transmit the light. However, when ultra-short pulses of modest energy of this same light (for example 100 fs, 1 muJ laser pulses) are tightly focused int...

A confocal fluorescence microscopy setup was used to observe, in situ, spectral changes in phosphate glasses which were modified using 0.3 μJ of tightly focused 800 nm, 130 fs laser pulses. On 488 nm excitation, the modified glass shows a broad fluorescence centered at roughly 600 nm, which decays with prolonged exposure to the 488 nm light. The de...

The use of fs lasers to directly write phonic structures inside a glass has great potential as a fabrication method for three-dimensional all-optical integrated components. The ability to use this technique with different glass compositions --specifically tailored for a specific photonics application -- is critical to its successful exploitation. C...

We report on three-dimensional fluorescence imaging of micron-size faceted crystals precipitated from solutions of CdSe nanocrystals. Such crystals have previously been suggested to be superlattices of CdSe quantum dots [1,2]. Possible applications for these materials include their use in optical and optoelectronic devices. The micron-size crystals...

Modified lines were written inside Corning 7940 fused silica with 130 fs laser pulses from an amplified Ti–sapphire laser operating at 800 nm at a repetition rate of 1 kHz. The sample was scanned at 20 µm s−1 with laser pulse energies ranging from 1 to 35 µJ, resulting in modified lines with diameters ranging from 8 to 40 µm. Confocal fluorescence...

We report on the response of glass to focused femtosecond (fs) laser pulses during waveguide fabrication in a commercial sodium aluminum phosphate glass (Schott IOG-1). Single-pass longitudinal translation of IOG-1 glass with respect to the focused laser beam at a rate of 20 μm/s and pulse energies of 3.5 μJ results in the formation of two waveguid...

We describe a multiwavelength, multifiber (parallel) optical interconnect based on multimode fiber ribbon cables with applications in massively parallel processing systems. By combining the benefits of parallel optics and coarse wavelength division multiplexing high aggregate throughputs are possible in a broadcast and select architecture that prov...

Atomic-scale structural changes have been observed in the glass network of fused silica after modification by tightly focused 800-nm, 130-fs laser pulses at fluences between 5 and 200J cm-2. Raman spectroscopy of the modified glass shows an increase in the 490 and 605-cm-1 peaks, indicating an increase in the number of 4- and 3-membered ring struct...

Second-order optical nonlinearities (χ(2)) were induced in commercial phosphate glasses (Schott, IOG-1) by the thermal poling technique. Maker fringe experiments were used to characterize the induced nonlinear regions. The results show that a near-anodic surface and a bulk χ(2) are formed that are opposite in sign. The strength of the near-anodic s...

Second-order nonlinearities were induced in lanthanum phosphate and sodium aluminum phosphate glasses. Maker fringe experiments show that the induced nonlinearities in the two glass systems have different magnitudes and spatial profiles. The microscopic origin of X(2) is discussed in terms of different charge migration models.

We describe a postgrowth method to produce passband filters with different center wavelengths from a single growth run by irreversibly changing the refractive index of a layer or a series of layers within the filter. This leads to a new type of filter, the passband-shifting filter, whose center wavelength can be irreversibly shifted from λ 0 to λ 0...

Refractive index changes have been induced inside bulk fused silica by using femtosecond (fs) laser pulses tightly focused inside the material. Waveguides have been fabricated inside the glass by scanning the glass with respect to the focal point of the laser beam. The refractive index change is estimated to be 10. Other more complex three-dimensio...

Summary form only given. The objective of our research is to introduce a second-order optical nonlinearity (χ(2)) in phosphate glasses via the thermal poling technique, in order to enable the fabrication of integrated waveguide frequency-doubled lasers. The induced second order nonlinearities were measured via second harmonic generation using a fun...

Tightly focused femtosecond (fs) laser pulses have been used to fabricate waveguides inside two bulk glasses: fused silica (Corning 7940) and a phosphate glass (Schott IOG-1). Using a confocal microscopy set-up, we have measured Raman and fluorescence spectra of the modified regions in the glass. The spectroscopic changes give information about the...

Using in situ Raman scattering in a confocal microscopy setup, we have observed changes in the network structure of fused silica after modifying regions inside the glass with tightly focused 800-nm 130-fs laser pulses at fluences of 5 – 200 J cm - 2 . The Raman spectra show a large increase in the peaks at 490 and 605 cm - 1 , owing to 4- and 3-mem...

form only given. We have written waveguides as long as 1 cm in silica glasses by tightly focusing femtosecond laser pulses from a regeneratively amplified Ti:sapphire laser (125 fs, 800 nm, 1 kHz) using a microscope objective and translating the glass parallel to the laser beam. For our experiments laser pulse energies range from 0.5-3 /spl mu/J an...

We report on the application of phosphate glass Schott IOG-1 as a host material for glass-based integrated waveguide devices. The fabrication of such devices requires the combination of different optical functions in one material. Channel waveguide lasers were fabricated in Nd3+:IOG-1 using a field assisted Ag+ ion exchange process. Lasing was achi...

Lasing of Fe:ZnSe is demonstrated, for the first time to the authors’ knowledge, for temperatures ranging from 15 to 180 K. The output wavelength of the Fe:ZnSe laser was observed to tune with temperature from 3.98 µ m at 15 K to 4.54 µ m at 180 K. With an Er:YAG laser operating at 2.698 µ m as the pump source, a maximum energy per pulse of 12 µ J...

WDM filter modules are presented for multimode fibre ribbon cables which employ a simple package and provide low crosstalk and sharp passband edges, suitable for 10 nm channel spacing. These devices exhibit low insertion loss (1.6 dB average) and good wavelength uniformity (±0.8 nm)

Our WDM filter approach is based upon post-market machining of the commercially available molded plastic “MT” fiber ribbon connector. Current work focuses on 2-port WDM filters suitable for a broadcast and select architecture. To improve crosstalk suppression beyond that attainable with the Lorentzian lineshapes of the single-cavity FP we have inve...

We report on the laser performance of a Nd:phosphate glass (Nd:IOG-1) channel waveguide laser fabricated by electric field assisted Ag{sup +} diffusion. Lasing was achieved in two different size channels, 29 x 9 μm² and 50 x 9 μm², on a sample of length 8 mm. Slope efficiencies of ⼠15% with respect to incident pump power were measured. Losses...

We report on planar waveguides formed by field assisted ion exchange in Nd{sup 3+} and Yb{sup 3+} doped phosphate glasses. Losses of 0.71 dB/cm are measured. Electron probe measurements confirm Ag{sup +} diffusion.

We report on planar waveguides formed by field assisted ion exchange in Nd3+ and Yb3+ doped phosphate glasses. Losses of 0.71 dB/cm are measured. Electron probe measurements confirm Ag+ diffusion.

Solid-state waveguide lasers offer several attractive features that may make high efficiency and effective thermal management possible. Due to the ability to confine pump light to high intensity over distances much longer than the Rayleigh range, as well as maintaining good overlap between the pump and Iasing modes over the entire guiding region, e...

We have investigated the influence of Nd: YAG laser light at 1064 nm on the growth and erasure of x(2) gratings using 790/ 395-nm light in Tm-doped fibers. The addition of 1064-nm light to the writing pair of 790/395 nm was observed to cause at most a slight increase in writing speed in a low-Tm (4 ppm) fiber; Nd: YAG irradiation was furthermore ob...

Raman spectroscopy was performed on the cores of germanosilicate optical fibers into which molecular hydrogen was diffused and subsequently treated with either heat or low-intensity ultraviolet light at 254 nm. The results indicate that distinctly different hydrogen addition reactions occur in these two cases. Thermally initiated reactions resulted...

We have investigated the influence of Nd:YAG laser light at 1064 nm on the grating growth and erasure processes for 790/395-nm light in Tm-doped fibers. The addition of 1064-nm light to the writing pair of 790/395 nm was observed to cause at most a slight increase in writing speed in a low-Tm fiber; in a high-Tm fiber, however, it caused a rapid dr...

We report a 10³ increase in efficiency of second-harmonic generation in Tm³⁺-doped aluminosilicate glass fibers when the wavelength of the fundamental beam is tuned to the maximum of the ³H6 → ³F4 absorption of Tm³⁺ at 785 nm. This result shows the role of resonance enhancement in the nonlinear optical process that is responsible for the formation...

Permanent photoinduced optical attenuation has been observed in Tm³⁺-doped aluminosilicate glass fibers on exposure to near-resonance mode-locked 1064-nm radiation at 300 K. The rate of this darkening was observed to follow a 4.7 ± 0.4 power dependence on the 1064-nm intensity. The result shows that absorption of infrared light of moderate intensit...

The process of the generation of metastable phase-matched second-order nonlinear susceptibilities in glasses by shining light is shown to follow from general symmetry and variational condiderations. Microscopic models proposed for this phenomenon are discussed in this framework.

We study saturation of photoinduced second-harmonic generation in a Ge-doped silica fiber by modulating the relative phase between the fundamental and second-harmonic writing beams. We shift the phase by π and present measurements that identify saturation that is due to site depletion and saturation that is due to a backfield.

Photoinduced χ ⁽²⁾ gratings can be written in optical fibers by simultaneous irradiation with beams at co and 2ω. Although this phenomenon is not understood in detail, the experimental results show that the presence of optically active centers in the fiber is essential for the observation of this effect. We have studied photoinduced SHG in rare ear...

We have measured the efficiency of photoinduced second-harmonic generation (SHG) in Ge- doped silica fibers containing different concentrations of 'GeO' and 'GeH' defects. The relative concentration of these defects were varied by heat treatments in H2 and determined using luminescence spectroscopy. The results show that the GeH defect center, whic...

The nonlinear optical properties of glass have recently become the focus of growing scientific and technological interest. Nonlinear properties include intensity-dependent refractive index, multiphoton absorption, second- and third-harmonic generation, stimulated Raman and Brillouin scattering, and associated phenomena such as self-focusing, self-p...

The presence of defect states in the band gap is an essential ingredient of recent models of photoinduced second-harmonic generation (SHG) in fibers. We have created such states by doping aluminosilicate glass fibers that do not contain Ge with Ce or Eu and observed SHG from 1.06-μm light after preparation of the fibers with 0.532- and 1.06-μm ligh...

The structure of sodium aluminosilicate gels of various composition, prepared by sol-gel methods using TEOS and nitrates, was studied with Raman spectroscopy. Some of these gels, 12.5Na2O12.5Al2O375SiO2 (albite) and 7.5Na2O7.5Al2O385SiO2, can be easily densified into glasses by heat treating them at 1100°C. The similarity between Raman spectra...

Phase fluctuations between the infrared and green beams during seeding of second-harmonic generation (SHG) in optical fibers lead to a drastic reduction of the initial SHG intensity and to a strong time dependence of the SHG after seeding. Experiments using mode-locked lasers with a stable phase relation between the infrared and green writing beams...

Permanent X(2) gratings can be written in doped silica fibers by coherent irradiation with light at ω and 2ω. The X(2) gratings give rise to phase-matched second harmonic generation (SHG), i.e. subsequent irradiation of the prepared fiber with light at ω results in an output at 2ω. The efficiency with which the gratings can be written depends on th...

The presence of defects in glass optical fibers is considered a key factor for the observation of photoinduced SHG. ¹ Most studies have ben concerned with Ge-doped silica fibers in which Ge-defects are the active species. Recently we have reported photoinduced SHG in rare earth-doped optical fibers that do not contain Ge. ² Conversion efficiencies...

We have measured the nonlinear refractive index (n 2 ) of single crystalline poly(bis(p‐toluene sulfonate) of 2,4‐hexadiyn‐1,6‐diol) (PTS) polydiacetylene channel waveguides at 1.06 μm using two different techniques. The first method employs a Mach–Zehnder interferometer to determine the intensity‐induced phase shift in the waveguide. In the second...