(b) Write out the equations for the time dependence of ρ11, ρ22, ρ12 and ρ21 assuming that a light field interaction V = -μ12Ee iωt + c.c. couples only levels |1> and |2>, and that the excited levels exhibit spontaneous decay. (8 marks) (c) Under steady-state conditions, find the ratio of populations in states |2> and |3>. (3 marks) (d) Find the slowly varying amplitude ̃ ρ 12 of the polarization ρ12 = ̃ ρ 12e iωt . (6 marks) (e) In the limiting case that no decay is possible from intermediate level |3>, what is the ground state population ρ11(∞)? (2 marks) 2. (15 marks total) In a 2-level atom system subjected to a strong field, dressed states are created in the form |D1(n)> = sin θ |1,n> + cos θ |2,n-1> |D2(n)> = cos θ |1,n> sin θ |2,n-1>

The Quantum Theory of Light

1: Magnetic Particles: Preparation, Properties and Applications: M. Ozaki. 2: Maghemite (gamma-Fe2O3): A Versatile Magnetic Colloidal Material C.J. Serna, M.P. Morales. 3: Dynamics of Adsorption and Oxidation of Organic Molecules on Illuminated Titanium Dioxide Particles Immersed in Water M.A. Blesa, R.J. Candal, S.A. Bilmes. 4: Colloidal Aggregation in Two-Dimensions A. Moncho-Jorda, F. Martinez-Lopez, M.A. Cabrerizo-Vilchez, R. Hidalgo Alvarez, M. Quesada-PMerez. 5: Kinetics of Particle and Protein Adsorption Z. Adamczyk.

Surface and Colloid Science

In the laser treatment of a workpiece (9), e.g. for surface hardening, melting, alloying, cladding, welding or cutting, the adverse effect of reflectivity of the surface, when a pure, monochromatic laser (6) is used, is remedied by the simultaneous application of a relatively shorter wavelength beam (1). The two beams (1)(5) may be combined by a beam coupler (4) or may reach the workpiece (9) by separate optical paths (not shown). The shorter wavelength beam (1) improves the coupling efficiency of the higher- powered laser beam (5).

Laser Material Processing

Journal of Physics Condensed Matter: Preface

The photoinduced surface wettability conversion reactions of ZnO and TiO2 thin films were investigated by means of water contact angle measurement and X-ray photoelectron spectroscopy. Before ultraviolet (UV) illumination, ZnO and TiO2 films exhibited water contact angles of ∼109 and ∼54°, respectively. UV illumination turned both surfaces to highly hydrophilic with water contact angles smaller than 10°. Storage in the dark reconverted the highly hydrophilic films to their original states. Reversible surface wettability conversion reactions were achieved by alternate UV illumination and storage in the dark on both the films. The similar behaviors of wettability conversion observed on ZnO and TiO2 surfaces suggest that they follow a similar conversion mechanism. Preferential adsorption of water molecules on the photogenerated surface defective sites is ascribed to the formation of highly hydrophilic ZnO and TiO2 surfaces. Achievement of highly hydrophilic ZnO and TiO2 surfaces by high-temperature annealing...

Photoinduced Surface Wettability Conversion of ZnO and TiO2 Thin Films

This work elucidates the basic mechanisms active in microstructure and the associated surface energy for a widely used bioinert ceramic, magnesia partially stabilized zirconia (MgO–PSZ) following CO2 laser treatment. CO2 laser irradiation results in rapid heating of the surface and consequently leads to the surface densification and crystal growth in the melted layer of the MgO–PSZ. There was an increase in the tetragonal phase after CO2 laser treatment and columnar crystal structure in the upper-most layer and irregular grain in the heat affected zone. Various power densities of laser treatment brought about different microstructures on the modified MgO–PSZ. Contact angle measurement of a set of test liquids was used to estimate the surface energy of the MgO–PSZ before and after CO2 laser treatment. It was found that the surface energy of MgO–PSZ had been enhanced after CO2 laser treatment and its increase was related to the phase change (represented by microstructure) and crystal size of MgO–PSZ.

On the role of microstructure form and dimension in surface energy changes in a magnesia partially stabilized zirconia bioceramic following CO2 laser irradiation

Due to their attractive mechanical properties, bioinert zirconia bioceramics are frequently used in the high load-bearing sites such as orthopaedic and dental implants, but they are chemically inert and do not naturally form a direct bond with bone and thus do not provide osseointegration A CO2 laser was used to modify the surface properties with the aim to achieve osseointegration between bioinert zirconia and bone The surface characterisation revealed that the surface roughness decreased and solidified microstructure occurred after laser treatment Higher wettability characteristics generated by the CO2 laser treatment was primarily due to the enhancement of the surface energy, particularly the polar component, determined by microstructural changes An in vitro test using human fetal osteoblast cells (hFOB) revealed that osteoblast cells adhere better on the laser treated sample than the untreated sample The change in the wettability characteristics could be the main mechanism governing the osteoblast cell adhesion on the YPSZ

Osteoblast cell adhesion on a laser modified zirconia based bioceramic.

The surface of the bio-material polymethyl methacrylate (PMMA) was treated with CO2, Nd:YAG, excimer and high power diode laser (HPDL) radiation. The laser radiation was found to effect varying degrees of change to the wettability characteristics of the material depending upon the laser used. It was observed that interaction with CO2, Nd:YAG and HPDL effected very little change to wettability characteristics of the PMMA. In contrast, interaction of the PMMA with excimer laser radiation resulted an increase in a marked improvement in the wettability characteristics. After excimer laser treatment the surface O2 content was found to have increased and the material was seen to be more polar in nature. The work has shown that the wettability characteristics of the PMMA could be controlled and/or modified with laser surface treatment. However, a wavelength dependence of the change of the wetting properties could not be deduced from the findings of this work.

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Modification of the wettability characteristics of polymethyl methacrylate (PMMA) by means of CO2, Nd:YAG, excimer and high power diode laser radiation

The factors responsible for modifications to the wettability characteristics of a titanium (Ti6Al4V) alloy bio-metal following Nd:YAG laser treatment and the effects thereof on the response of osteoblast cells were considered in this work. It was found that interaction of the Nd:YAG laser beam with the Ti6Al4V alloy resulted in the wettability characteristics of the bio-metal improving. Such improvements in the wettability characteristics of the Ti6Al4V alloy were found to be due to: an increase in the surface roughness; and increase in the surface oxygen content and an increase in the polar component of the surface energy. From the cell response tests it was determined that the osteoblast cell adhesion and proliferation on the Nd:YAG laser treated Ti6Al4V alloy samples was considerably greater than on the untreated samples. By isolating the effects of surface roughness it was possible to confirm or refute the existence of a correlation between wettability characteristics and osteoblast cell bioactivity for the Nd:YAG laser treated Ti6Al4V alloy. The findings indicated that the aspects of wettability characteristics: surface oxygen content and polar component of the surface energy play an important role in promoting cell proliferation, particularly when surface roughness was simultaneously increased. Thus it was possible to conclude that the wettability characteristics of the Nd:YAG laser treated Ti6Al4V alloy were correlated to osteoblast cell bioactivity.

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On the correlation between Nd:YAG laser-induced wettability characteristics modification and osteoblast cell bioactivity on a titanium alloy

This paper is focused on laser shock peening (LSP) of titanium alloy (Ti-6Al-7Nb) for the first-time. This was to improve upon the artificial implant failures caused by destitute wear resistance of titanium alloys. As such, millions of patients are suffering from osteoarthritis pain, which costs billions of pounds annually to end users as they either have to undergo a complete replacement of the particular implants or a second surgery subject to implant failures. Therefore, the effect of multiple impacts on the mechanical properties and sliding wear behaviour of Ti-6Al-7Nb subjected to LSP were investigated. Ti-6Al-7Nb has the advantage of biocompatibility as the material can be applicable for orthopaedic implants. It is critical to improve the mechanical properties and wear resistance. LSP is one of the most effective methods to improve mechanical properties. Thus, in this study X-ray diffraction (XRD); Scanning Electron Microscope (SEM); surface roughness using 3-D profiling; microhardness using Vickers indentation method; and sliding wear with a tribometer were employed to measure the effect of Ti-6Al-7Nb alloy subjected LSP. It was found that the microhardness of Ti-6Al-7Nb alloy can be effectively improved from 290 HV30 to 369 HV30. In addition, the average the grain size was measured to be 10 μm and showed a reduction of 67%. The surface roughness was increased after multiple LSP from 0.15 μm to 0.52 μm. However, the wear resistance was improved by 44% after multiple LSP. The findings from this work will contribute towards extending the services time of orthopaedic implants and help patients undergo reduced number of surgeries.

Jonathan Lawrence

Papers

On the role of microstructure form and dimension in surface energy changes in a magnesia partially stabilized zirconia bioceramic following CO2 laser irradiation

Osteoblast cell adhesion on a laser modified zirconia based bioceramic.

Modification of the wettability characteristics of polymethyl methacrylate (PMMA) by means of CO2, Nd:YAG, excimer and high power diode laser radiation

On the correlation between Nd:YAG laser-induced wettability characteristics modification and osteoblast cell bioactivity on a titanium alloy

Improvement in mechanical properties of titanium alloy (Ti-6Al-7Nb) subject to multiple laser shock peening