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Thermal lensing investigation on bulk ceramics and thin-film PLZT using visible and far-infrared laser beams
Abstract
The real-time thermo-optical properties of thin-film relaxor ferroelectric (9/65/35) lead lanthanum zirconate titanate (PLZT) films (∼2 μm) were investigated and compared to identical composition of thick PLZT ceramics (∼1 mm). Since PLZT absorbs strongly in the far-infrared, a CO2 laser beam (λ = 10.6 μm) was used to create a Gaussian temperature distribution at the surface of the material, emulating a lens. Subsequently, a low power visible He–Ne laser, travelling along the same path as the CO2 laser, probed the optical properties of the induced PLZT thermal lens. It was found that identical composition thin-film and thick PLZT ceramics have opposite thermal lensing behaviors. An explanation of this phenomenon is provided from basic physical concepts.
... He and his colleagues published series of articles concerning the appearance of aberration pattern ( rotation of the plane of polarization, time dependences of the intensity of the central spot, and elongation of the aberration rings) formed as a result of self-focusing of a light beam caused by the Fréedericksz transition [2][3][4][5][6][7][8]. For various reasons the diffraction pattern in the shape of concentric rings was studied, viz, strong self-defocusing effect and foure-wave mixing in bacteriorhodopsin films [9] absorbing solution [10], optical multistability in nematic liquid crystal [11], organically modified sol-gel materials [12], mercury dithizonate [13], femtosecond Bessel beams [14], self-focusing spatial beams [15] and bulk ceramic and thin film PLZT [16]. There is considerable interest in finding materials ...
E Ex xp pe er ri im me en nt ta al l a an nd d T Th he eo or re et ti ic ca al l S St tu ud dy y o of f t th he e L La as se er r I In nd du uc ce ed d D Di if ff fr ra ac ct ti io on n P Pa at tt te er rn n i in n t th he e A Ac ci id d O Or ra an ng ge e 1 10 0 D Dy ye e: : P Po ol ly ya ac cr ry yl la am mi id de e G Ge el l Abstract: We observed and studied diffraction rings generated in an Acid Orange 10 dye doped Polyacrylamide gel (AO10: PAA gel) using cw visible laser beam. The number of rings increases almost exponentially with increasing input power and concentration of the samples. The refractive index change, ∆n, effective nonlinear refractive index, nR 2 R, variation of thermo-optic coefficient ,dn/dT, figure of merit ,W, and thermal figure of merit ,H, are found to be 0.004788 , 10P-5 P cmP 2 P /Watt, 1.01×10P-4 P 1/P o P C, 13.7 and 0.45×10P-4 P respectively. The effective nonlinear refractive index, nR 2 R, was determined based on the observed number of rings. This large nonlinearity is attributed to a thermal effect. Theoretical diffraction patterns that agree well with experimental one are generated using a wave theory.
... A directional beam that can target the volume of a region and can control temperature in the same time would become a powerful tool in clinical trials. The power of this technique with these two lasers working in tandem was applied successfully in thermal lensing [21] in a PLZT sample having a thickness ranging from 2 μm to 1 mm. From these previous findings, the method being proposed could also be useful to process materials, which absorb the CO 2 wavelength at λ 10.6, 9.6, or 9.3 μm from commercially available CO 2 lasers. ...
Temperature of water-based substances is investigated by aiming a pulsed laser beam at the water–air surface. This method of controlling temperature is believed to be flexible in medical applications as it avoids the use of thermal devices, which are often cumbersome and generate rather larger temperature swing with time. The control of temperature in this laser method is modeled by the heat conduction equation. In this investigation, it is assumed that the energy delivered by the laser is confined within a very thin surface layer of roughly 10 μm. It is shown that the temperature can be very well controlled by a laser at a steady temperature, and we demonstrate that the method can be adapted to work in tandem with another laser beam.
... In this chapter, I will conduct a review on some of the fundamental material properties of relaxor ferroelectric PLZT ceramics, which include the dielectric, ferroelectric, electromechanical, electro-optical and thermo-optical behaviours. Further details on each section can be found in the references (Lévesque and Sabat 2011; Sabat, Rochon, and Mukherjee 2008 ...
The operating principles for photothermal spectroscopy of solids and heterogeneous materials are considerably different from those of the homogeneous samples. Several types of heterogeneity should be considered when analyzing solid samples. It is possible for heterogeneous samples only with control over the sample thermal properties and elaborate mathematical treatment of the data. This chapter addresses the theory for the temperature change and photothermal deflection spectroscopy signal production. Photothermal spectroscopy of surface and bulk absorbing samples can be used to quantitate the absorbance of the solid sample. Another interesting sample type is that of the layered sample. The methods for finding the temperature change for the surface point source can be applied to situations where a pulsed or continuous Gaussian profile laser beam is used to excite a sample with surface absorption. The chapter ends with a short survey of the analytical applications of the photothermal techniques used for heterogeneous sample analysis.
Optical bistability in PLZT ceramics due to the Ar laser induced heating and changes of the optical thickness of a plane parallel PLZT plate (behaving as the Fabry-Perot cavity) is observed. Such PLZT ceramics plate is used also as an extracavity laser mirror. Thermooptical tuning of the mirror causes a non-liner behaviour of such system. A negative feedback brought by the thermooptic mirror can be used to stabilise the laser output. On the contrary, the competitive action of the PLZT plate as the coupled mirror, on one hand, and as the non-linear Fabry-Perot cavity, on the other hand, can cause periodical fluctuations in the output of the laser.
Thermal lensing in relaxor type ferroelectrics as a function of temperature has been investigated by using pulse/probe method. Enhanced thermo-optical (TO) properties had been observed in 3d elements (Cu, Co) doped PLZT ceramics and in sodium-bismuth titanate single crystals near phase transitions (PT). Comparison of TO signals for several doped PLZT materials reveals that 0.5 wt.% Cu doping is responsible for improved thermal lensing parameters interpreted by optimal light absorption, heat transfer and possible PT adjustment. TO experiments in sodium-bismuth titanate single crystals ([001] cut) show enhancement of TO properties in the region of PT and coexisting phases (rhombohedral and tetragonal).
Transition lines between various phases in the electric-field?temperature
phase diagram of 9/65/35 lanthanum lead zirconate titanate
ceramics were determined by measurements of the temperature and
electric-field?dependent dielectric constant. Above the critical field
(EC) the dc bias electric field induces a transition from the relaxor
to the ferroelectric phase, while below EC the system exhibits a freezing
transition between the ergodic and nonergodic relaxor state. Transition
lines are discussed in terms of the spherical random-bond?random-field model
of relaxor ferroelectrics. Measurements in the quasistatic temperature
regime confirm the prediction of the model that the nonlinear dielectric
response shows a sharp peak at the freezing transition temperature.
A thorough investigation of optical losses for the 1064 nm emission in Nd 3 + -doped lead lanthanum zirconate titanate (PLZT) transparent ceramics is presented. Thermal lens experiments were carried out to evaluate thermo-optical properties and the fluorescence quantum efficiency of the emitting level F 3 ∕ 2 4 . Excited-state absorption losses were measured in the emitting wavelength region, and the Auger upconversion energy transfer parameter γ was calculated. By using γ, the pump-intensity dependence of the optical gain at 1064 nm , the fluorescence quantum efficiency, and the generation of heat in the ceramic were simulated for a high 803 nm pump-power regime. Since the radiative and nonradiative losses in Nd : PLZT were verified to be considerably lower than in various commercial laser crystals and glasses, it is suggested that this material might become an interesting alternative for high-power laser emission.
Thermo-optical phenomena in absorbing media containing nanosize ferromagnetic or ferroelectric particles in liquid or solid state matrix are investigated. Enhanced thermo-optical properties have been observed in lanthanum doped lead zirconate-titanate (PLZT) ceraMisc, sodium-bismuth titanate single crystals and ferrofluids near phase transitions.
System, device, and material issues for the design and realization of smart spatial light modulators are discussed. Silicon and lead lanthanum zirconate titanate (PLZT) are two promising materials that meet the system requirements. Two different technologies for the integration of Si and PLZT are described. Results show that large-scale smart spatial light modulators can be realized with Si/PLZT technologies.
Single crystals of SbSI have shown large changes in refractive index through the paraelectric–ferroelectric transition for light polarized parallel to the ferroelectric c axis. Near the absorption edge, the observed change is discontinuous. Large changes in refractive index can also be induced by pulsed electric fields along the c axis. The extreme anisotropy of SbSI is indicated by the large partial birefringences observed in the paraelectric phase.
Relaxor lead lanthanum zirconate titanate (PLZT) thin films, with compositions of ( 7 / 65 / 35 ), ( 8 / 65 / 35 ), and ( 9 / 65 / 35 ), have been investigated as optical waveguides. Resonant structures were observed in the reflected light beam that passes through these thin films after coupling with a laser-inscribed azo polymer surface relief diffraction grating. The temperature was then varied on the PLZT thin films between − 20 and 70 ° C , and a shift in the above resonance peaks was observed that is due to a change in the refractive index of the samples. The temperature dependence of the refractive index of the tested PLZT thin films was subsequently plotted and was found to decrease linearly with an increase in temperature at different rates for all the thin-film compositions tested.
This review of the PLZT materials and their applications describes the present state of the technology and emphasizes the latest developments in the field of electrooptic ceramics. Despite the reported development of new, transparent materials in other compositional systems, the PLZT's still remain the standard of the industry and continue to find an ever increasing number of applications in the areas of shutters, filters, displays, and spatial light modulators. Their fast response, high resolution and wide operating temperature range make them viable candidates for several emerging technologies including high resolution, non-impact, facsimile printing, electrophotographic copying, color reproduction and integrated optical processing. With the presently successful development of sputtered PLZT thin films, both bulk and thin film PLZT materials can now be considered for future electrooptic devices.
In this work thermal lens spectrometry, thermal relaxation calorometry and optical interferometry were employed to determine the thermo-optical properties of transparent PLZT 10/65/35 ceramics. The thermal diffusivity, the specific heat and the temperature coefficient of the optical path length change were determined. These parameters are important to obtain the figure of merit of this material in terms of its application as optical components used under high power laser excitation.
Local confinement of the electromagnetic fields in a waveguide is a boundary condition problem which is often discussed as an example of wave propagation. A wave can also propagate in the air in a region without boundaries. In this case, the beam of electromagnetic waves is merely diverging as no condition of total internal reflection exists in a uniform medium such as air. We develop equations predicting the proper separation distance between a pair of lenses to collimate a far-infrared laser beam for both a Galilean and Keplerian telescopic systems. For a typical CO2 laser Gaussian beam at λ=10.6μm, it is found that the separation distance is much more than the simple sum of the focal lengths for both lenses used in a given telescopic system. This substantial increase in the separation distance between the pair of lenses is mostly due to the divergence of the emitting radiation of the CO2 laser in the air, which is large compared to that of other commercially available laser sources. Some experimental results are given for both the Galilean and Keplerian telescopes and the discrepancies are compared from the calculations. A simple methodology is also described to test the collimation of the invisible CO2 laser beam after it is transmitted through the pair of collimated ZnSe lenses. Good estimations for the separation distance between a pair of collimation lenses and beam magnifications are very useful when focusing a beam of CO2 laser to a very small spot in various designs, where high-power density is required. Computations for the separation distance and magnification are found to be very close to the experimental values reported with a discrepancy of less than 4%.
Changes in the refractive indices Δn1 and Δn3 of clamped transparent relaxor ferroelectric (9.5/65/35) and (9.0/65/35) PLZT ceramics were measured as a function of temperature ranging from −30°C to 60°C, and at various transversely applied DC electric fields E3DC. It was found that the refractive index of both PLZT compositions increased linearly with temperature under no DC bias, indicating a constant electronic polarizability of the samples in the tested temperature range. The rate of increase of Δn3 with temperature became higher for both compositions upon the application a DC bias field (E3DC=774kV/m) due to increased electronic polarizability of the samples, while the rate of increase of Δn1 with temperature remained unchanged and was independent of the DC field applied. The quadratic electro-optic coefficients of these two PLZT compositions were also obtained at 0, 20 and 40°C, and a significant non-linearity was observed: an 85% decrease in the electro-optic coefficient of PLZT (9.5/65/35) was measured at 40°C compared to 0°C, while a similar 60% drop was measured for PLZT (9.0/65/35).
Transparent ferroelectric ceramic materials suitable for a variety of electrooptic applications were found in the quaternary (Pb,La)(Zr,Ti)O3 system. These PLZT materials are prepared from mixed oxides and hot-pressed typically at 1100°C for 16 h at 2000 psi. Modifying the lead zirconate-titanate system with lanthana linearly reduces the Curie point with increasing lanthana. Transmission measurements in the visible and infrared show that these materials exhibit a nearly constant response from the absorption edge of 0.37 μ to ∼6 μm. The highest transmission values, essentially 100% (neglecting reflection losses of ∼18%) for thin polished plates, were noted for compositions containing 8 at.% La or more. Specific compositions within the system display electrooptic memory or conventional linear or quadratic electrooptic effects; on the basis of the magnitude of the electrooptic effects, they compare quite favorably with single crystals.
Physical, electrical, and optical properties of selected compositions within the lead lanthanum zirconate-titanate (PLZT) system are presented, including chemically and thermally etched microstructures, examples of residual porosity defects, temperature dependence of remanent polarization and coercive field, lateral switching strains, and thermal expansion and optical transmission data. Optical-quality ceramics were produced by stringent raw material selection and improved ceramic processing and hot-pressing. Optimum results were obtained from starting oxides with higher purity (99.9%) and smaller particle size (<2 μm) than those used in previous investigations. These oxides were processed by methods developed to minimize segregation and promote chemical homogeneity and hot-pressed at temperatures (1050° to 1250°C) higher than those used previously to remove residual porosity.
This paper gives a detailed summary of the International Standardization Organization working draft concerning measurement methods for laser beam width, divergence and propagation factor. Some of the important reasons for the multiple methods included in the draft are presented. A comparison of the differences between various definitions of, and methods for, measuring beam width is given. The document is not yet final and comment on the definitions and methods proposed is invited.
The refractive index and the optical energy gap of Pb1–x
Ge
x
Te (0x0.11) have been determined from transmission- and reflectivity measurements in the temperature range from 4.2 K to 300 K. At the ferroelectric phase transition a change of the temperature coefficient of both quantities is observed. A two bandkp model calculation demonstrates a correlation of the optical energy gap with the high frequency dielectric constant. For higher values ofx (x=0.09) a splitting of absorption edge and birefringence have been observed.
Ferroelectric PLZT thin films were prepared onto Pt and fused‐quartz substrates by the rf sputtering method using powder targets with a few wt% of excess PbO. The structures of films were analyzed by x‐ray diffraction and classified into three types depending on substrate temperatures: the perovskite type (PLZT); the pyrochlore type, and the coexistence of both types. For the preparation of PLZT thin films, the substrate temperature was kept above 550 °C. Excess PbO seemed to act as a flux for crystal growth. The Curie temperature and hysteresis loops of thin films were investigated and it was confirmed that ferroelectric PLZT thin films could be obtained without annealing.
Preparation of epitaxial PLZT thin films on sapphire has been investigated, and excellent ferroelectric properties such as piezoelectricity and electrooptic effect with high transparency were obtained in thin films. Moreover, a preparation process was developed involving the multitarget sputtering method, and strict control of film composition and epitaxial growth with the buffer layer of graded composition were performed. Using these PLZT thin films, some optical applications, including an acoustooptic deflector and an electrooptic guided-light switch, are shown.< >
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