S. Creekmore

Distortions in Z-scan spectroscopy

The sample imperfection induced distortions in the closed Z-scan curve are analyzed. It is found that both the magnitudes of the peak and valley transmittances and the shape of the curve are distorted significantly by the inhomogeneous thickness, the nonuniform nonlinearity, and the curved surfaces of the sample. The results suggest that the I-scan method is a more practical choice for the measurement of the third-order nonlinear susceptibility of an inhomogeneous sample.

Large pure refractive nonlinearity of nanostructure silica aerogel

The nonlinear refraction coefficient of silica aerogel was estimated to be ∼−1.5×10−15 m2/W (∼−3.67×10−9 esu) with a signal-beam z-scan spectroscopy. The third-order nonlinear refraction coefficient of nanostructure silica aerogel was almost five orders larger than the nonlinear refraction (χ3) of bulk material. The large nonlinear refraction with high nonlinear figure of merit is an ideal optical property for nonlinear optical applications.

Z-scan and four-wave mixing characterization of semiconductor cadmium chalcogenide nanomaterials

The possible physical origin of third-order nonlinearity of cadmium chalcogenide (Te, Se, and S) semiconductor nanocrystals were discussed based on the results of both Z-scan and degenerate four-wave mixing spectroscopies at 532, 775, 800, and 1064 nm in nanosecond, picosecond, and femtosecond time scale for nonlinear photonic applications.

I-scan measurements of the nonlinear refraction and nonlinear absorption coefficients of some nanomaterials

We give the analytical expressions of the nonlinear transmittance of materials through an aperture in the far field with finite aperture size. The result can be used under the conditions of and . Based on this equation, the nonlinear refractive index coefficients of some nanomaterials from both the closed I-scan and Z-scan measurements at 800 nm and 1064 nm were extracted, respectively. The obtained values from I-scan measurements are comparable with those from the Z-scan measurements. The nonlinear absorptions of these materials were also studied by fulfilling the open I-scan and Z-scan measurements. The advantages of I-scan technology were discussed.

Evaluation of nonlinear optical properties of cadmium chalcogenide nanomaterials

Abstract High quality semiconductor nanomaterials were synthesized through colloidal methods, and evaluated nonlinear optical properties for optical power limiting applications. The nonlinear refraction ( γ ) and the nonlinear figure of merit (FOM= γ / βλ ) of CdTe nanomaterials in toluene (∼8×10 −5 mol/l ) were estimated to be ∼−1×10 −13 m 2 / W and ∼200, respectively. The optical power limiting through CdTe nanoscale materials was mainly by the nonlinear refraction because of the high nonlinear FOM.

Nonlinear refraction and nonlinear absorption measurements of CdTe nanoscale materials embedded in PMMA using ultrafast laser pulse

Experimental investigations have shown that CdTe semiconductor microcrystals possess large third-order susceptibilities and short response times at both resonant and non-resonant wavelengths (580 nm and 1064 nm). These excellent properties indicate their potential applications in nonlinear photonic devices. In this work, we measured the nonlinear refraction and nonlinear absorption coefficients of CdTe nanocrystals using Z-scan method at 800 nm. Application in optical limiting of the sample was also demonstrated. The samples used were made by ball milling process and then embedded in polymethylmethacrylate (PMMA). The two photon absorption (TPA) and nonlinear refraction were evaluated from the normalized transmittance with open aperture and with closed-aperture, respectively. Optical limiting studies were carried out as a function of input intensity at 800 nm. The input intensities were varied from 5 to 70 kW/cm2. The transmitted power was collected by a photo-detector through a 2-mm diameter aperture. We found that the transmitted power decreased significantly over the input intensity range of 10-20 kw/cm2.

Nonlinear Optical Spectroscopy of Cadmium Chalcogenide Nanocrystals

We report on the nonlinear optical properties of cadmium telluride (CdTe) semiconductor colloidal quantum dots. Transmission electron microscopy measurements revealed that the size of CdTe nanocrystal quantum dots, dependent on the growth reaction time, was ∼2-10 nm or near the exciton Bohr radius. The strong blue-shifts of the CdTe, CdSe and CdS nanocrystal absorption spectra and the atomic-like discrete energy states of exciton indicate an exciton quantum confinement. These are completely different optical properties from the bulk crystals. The energy transition for exciton absorption was assigned as h 1 →e+, h 2 →e+, h 1 +→e-, and h 2 +→e- for the 1st, 2nd, 3rd and 4th exciton absorption peaks. Z-scan and I-scan nonlinear spectroscopy revealed that the CdTe nanocrystal quantum dot in toluene (∼8 × 10 -5 mol/L) has the negative nonlinearity (self-defocusing) with ∼ -1 × 10 -13 m 2 /W and a high nonlinear figure of merit of ∼200. For the optical power self-limiting experiment, the CdTe nanocrystal was almost opaque above ∼0.8 MW/cm 2 at the position of z∼6.9 cm.

Large pure refractive nonlinearity of nanostructure silica aerogel at near infrared wavelength

The nonlinear refraction coefficient of the third-order susceptibility of silica aerogel was estimated to be /spl sim/-1.5/spl times/10/sup -15/ m/sup 2//W (/spl sim/-3.67/spl times/10/sup -9/ esu) by a signal-beam z-scan technique with /spl sim/1 ps Ti:sapphire lasers. The third-order nonlinear refraction coefficient of nanostructure silica aerogel is almost five orders larger than the nonlinear (/spl chi//sup 3/) refraction of bulk material. The large nonlinear refraction originates mainly from the direct excitation to the surface trapped states, and the one-photon resonance process.

Large nonlinear optical susceptibility of SiO/sub 2/ aerogel

Summary from only given. The third-order nonlinear susceptibility of silica aerogel was measured by a single beam z-scan technique. The excitation source was 1 ps pulse of the Ti:sapphire laser operating at a wavelength of 800 nm.

Transition metal ion-doped cadmium-telluride saturable absorbers for passively Q-switched laser application

Summary form only given. To our knowledge, this is the first report of the saturable absorption properties of Cr-doped, and CoMn-codoped CdTe. TM-doped CdTe has a wider absorption band (/spl sim/1.5-2.5 /spl mu/m for Cr/sup 2+/ and /spl sim/1.4-2.5 /spl mu/m for Co/sup 2+/) compared with TM-doped ZnSe (/spl sim/1.4-1.9 /spl mu/m), and thus they can be operated as saturable absorbers over a wide mid-infrared spectral range. Moreover, a TM-doped CdTe binary compound is easier to grow compared to the CdMnTe ternary compound. We present the saturable absorption properties of Cr-doped, and CoMn-codoped CdTe at 2.09 /spl mu/m, for passive Q-switching. The saturation experiments at room temperature were carried out using a Cr,Tm,Ho:YAG laser. The ground state absorption (GSA) and the excited-state absorption (ESA) cross-sections, and bleaching factors were estimated. Transmittance as a function of energy fluence, without Fresnel loss correction, for Cr:CdTe and CoMn:CdTe are shown. Using Burshteins model of a slow saturable absorber, where a laser pulse is very short compared with the excited state decay time of the saturable absorber, and considering the background absorption, the bleaching factors of Cr/sup 2+/:CdTe and Co/sup 2+/ and Mn/sup 2+/:CdTe are estimated to be 1.57 and 1.67, respectively.