Laser-induced ferroelectric and photonic structures in lithium niobate crystals

The influence of laser illumination on ferroelectric domain engineering, waveguide formation and surface micro-structuring in lithium niobate (LN) is investigated. The ability to combine and to manipulate the size and depth of poling inhibited (PI) domains, which are produced by UV-laser irradiation of the +z face of congruent lithium niobate crystals followed by electric field poling, is demonstrated. It is therefore possible to produce complex domain structures, by partially overlapping individual UV laser irradiated tracks thus increasing the utility of this method for the fabrication of surface microstructures. Investigation of the electro-optic performance of ferroelectric/photonic composite structures, which occur naturally as a consequence of the PI process, had shown a significant enhancement (by ~ 36.7 % under the experimental conditions used) of the inherent electro-optic coefficient of the crystal attributed to large range stress at the domain boundaries. The feasibility of UV laser induced PI domain engineering in proton exchanged waveguides in LN was investigated showing that PI domain inversion is in principle possible. It requires however high laser intensity illumination which may produce significant surface damage. Additionally it was found that the proton concentration was also affected by the UV laser irradiation resulting in modifications of the original proton exchanged waveguide structure. Finally, an alternative to UV laser irradiation as a means for PI domain engineering and waveguide formation in LN is presented. This alternative method uses visible c.w. laser irradiation and an amorphous silicon absorbing layer to couple energy into the LN crystal thus emulating the direct absorption that occurs at UV wavelengths

Σιδηροηλεκτρικές και φωτονικές δομές επαγόμενες από ακτινοβολία λέιζερ σε κρυστάλλους νιοβικού λιθίου

The influence of laser illumination on ferroelectric domain engineering, waveguide formation and surface micro-structuring in lithium niobate (LN) is investigated. The ability to combine and to manipulate the size and depth of poling inhibited (PI) domains, which are produced by UV-laser irradiation of the +z face of congruent lithium niobate crystals followed by electric field poling, is demonstrated. It is therefore possible to produce complex domain structures, by partially overlapping individual UV laser irradiated tracks thus increasing the utility of this method for the fabrication of surface microstructures. Investigation of the electro-optic performance of ferroelectric/photonic composite structures, which occur naturally as a consequence of the PI process, had shown a significant enhancement (by ~ 36.7 % under the experimental conditions used) of the inherent electro-optic coefficient of the crystal attributed to large range stress at the domain boundaries. Τhe feasibility of UV laser induced PI domain engineering in proton exchanged waveguides in LN was investigated showing that PI domain inversion is in principle possible. It requires however high laser intensity illumination which may produce significant surface damage. Additionally it was found that the proton concentration was also affected by the UV laser irradiation resulting in modifications of the original proton exchanged waveguide structure. Finally, an alternative to UV laser irradiation as a means for PI domain engineering and waveguide formation in LN is presented. This alternative method uses visible c.w. laser irradiation and an amorphous silicon absorbing layer to couple energy into the LN crystal thus emulating the direct absorption that occurs at UV wavelengths.Η επίδραση της ακτινοβολίας λέιζερ στη μηχανική των σιδηροηλεκτρικών περιοχών, τον σχηματισμό κυματοδηγών και τη μικροδόμηση της επιφάνειας κρυστάλλων νιοβικού λίθίου διερευνώνται. Συγκεκριμένα, παρουσιάζεται η δυνατότητα συνδυασμού και χειρισμού του μεγέθους/βάθους περιοχών όπου αναστέλλουν την αναστροφή της πολωσιμότητας (PI), οι οποίες δημιουργούνται μέσω ακτινοβόλησης υπεριώδους ακτινοβολίας λέιζερ της +z επιφάνειας κρυστάλλων νιοβικού λιθίου, ακολουθούμενη από πόλωση του ηλεκτρικού πεδίου. Είναι επομένως δυνατό να παραχθούν πολύπλοκες δομές σιδηροηλεκτρικών περιοχών με μερική επικάλυψη μεμονωμένων ακτινοβολούμενων ιχνών, αυξάνοντας έτσι τη χρησιμότητα αυτής της μεθόδου για την κατασκευή μικροδομών. Επίσης διερευνάται η ηλεκτρο-οπτική απόδοση σιδηροηλεκτρικών/φωτονικών σύνθετων δομών, η οποία εμφανίζεται ως φυσική συνέπεια της διαδικασίας PI, επιδεικνύοντας σημαντική ενίσχυση (κατά ~36,7% υπό τις χρησιμοποιούμενες πειραματικές συνθήκες) του εγγενούς ηλεκτρο-οπτικού συντελεστή του κρύσταλλου. Παράλληλα, η δυνατότητα εφαρμογής της μηχανικής των σιδηροηλεκτρικών περιοχών επαγόμενης με υπεριώδους ακτινοβολίας λέιζερ σε κυματοδηγούς νιοβικού λίθιου ανταλλαγής πρωτονίων μελετήθηκε δείχνοντας ότι η αντιστροφή PI περιοχών είναι καταρχήν δυνατή. Ωστόσο παρατηρήθηκε ότι η υψηλής έντασης λέιζερ ακτινοβολία που απαιτείται μπορεί να προκαλέσει σημαντική ζημιά στην επιφανειακή ποιότητα του κρυστάλλου. Επιπρόσθετα, βρέθηκε ότι η συγκέντρωση πρωτονίων επηρεάστηκε από την υπεριώδη ακτινοβολία λέιζερ με αποτέλεσμα τη τροποποίηση της αρχικής δομής του κυματοδηγού. Τέλος, παρουσιάζεται ως εναλλακτική λύση της υπεριώδους ακτινοβολίας λέιζερ για στη μηχανική των PI σιδηροηλεκτρικών περιοχών και τον σχηματισμό κυματοδηγών στο νιοβικό λίθιο, χρησιμοποιώντας ορατής ακτινοβολίας λέιζερ σε συνδυασμό με ένα υμένιο απορρόφησης άμορφου πυριτίου

UV laser-induced poling inhibition in proton exchanged LiNbO3 crystals

The applicability of the UV laser-induced poling inhibition method for ferroelectric domain engineering in proton exchanged lithium niobate planar waveguides is investigated. Our results indicate that intense UV irradiation of proton exchanged lithium niobate samples can indeed produce poling inhibited domains in this material under certain irradiation conditions. However, there is strong indication that the temperature gradient that is formed during UV irradiation modifies the local proton concentration leading to changes in the refractive index profile of the original planar waveguide

UV laser-induced poling inhibition in proton exchanged LiNbO3 crystals

The applicability of the UV laser-induced poling inhibition method for ferroelectric domain engineering in proton exchanged lithium niobate planar waveguides is investigated. Our results indicate that intense UV irradiation of proton exchanged lithium niobate samples can indeed produce poling inhibited domains in this material under certain irradiation conditions. However, there is strong indication that the temperature gradient that is formed during UV irradiation modifies the local proton concentration leading to changes in the refractive index profile of the original planar waveguide

Non-Destructive Characterization of Selected Types of Films and Other Layers via White Light Reflectance Spectroscopy (WLRS)

In this work, we consider White Light Reflectance Spectroscopy (WLRS) as an optical methodology for the accurate, fast and non-destructive measurement of film thickness in the 1 nm to the 1 mm range and for applications that include microelectronics, photonics, bioanalysis and packaging. Films to which WLRS is applicable can be either homogeneous or layered-composite ones, while thickness and composition might be fixed or varying with time; in the latter case, real-time monitoring of the kinetics of processes such as certain transitions, film dissolution and bioreactions is possible. We present the basic principles of WLRS and a selection of characteristic application examples of current interest, and we also briefly compare WLRS with alternative methods for film measurement

Teratoma occupying the left hemithorax

<p>Abstract</p> <p>Background</p> <p>Teratomas are manifested with a great variety of clinical and radiological features, while sometimes they simply represent incidental findings.</p> <p>Case presentation</p> <p>A rare case of benign teratoma of the dermoid cyst type, in an adult 40-year-old female patient, is reported. The patient had presented recurrent pulmonary infections for the previous 2 months, persistent cough, and progressively aggravating dyspnea. A chest X-ray showed total atelectasis of the left lung, and the thoracic CT-scan revealed a huge mass, containing multiple elements of heterogeneous density, probably originating from the mediastinum, occupying the whole left hemithorax. The mass compressed the vital structures of the mediastinum, great vessels and airways, and a chest MRI was performed to accurately detect the anatomical relations. The patient underwent left thoracotomy and the tumor was totally resected. The size of the tumor was extremely large although no invasion to the vessels or to the airway had occurred. Adherence to the adjacent left pulmonary artery and left main bronchus was present, but without erosion or fistulization. The postoperative course was uneventful, while the histological examination confirmed a teratoma.</p> <p>Conclusion</p> <p>A teratoma is a non-homogeneous pathological entity, clinically, radiologically or histologically. It is predominantly diagnosed between the second and fourth decade and the incidence is equal for both sexes. Symptoms are absent in one half of the patients. The case reported is noteworthy as the tumor appeared with total atelectasis of the left lung, and symptoms started 2 months prior to diagnosis. Total removal of the tumor is adequate treatment for this type of teratoma and the prognosis is excellent.</p

Laser-induced ferroelectric domain engineering in LiNbO₃ crystals using an amorphous silicon overlayer

We report laser-induced poling inhibition and direct poling in lithium niobate crystals (LiNbO3), covered with an amorphous silicon (a-Si) light-absorbing layer, using a visible (488 nm) continuous wave (c.w.) laser source. Our results show that the use of the a-Si overlayer produces deeper poling inhibited domains with minimum surface damage, as compared to previously reported UV laser writing experiments on uncoated crystals, thus increasing the applicability of this method in the production of ferroelectric domain engineered structures for nonlinear optical applications. The characteristics of the poling inhibited domains were investigated using differential etching and piezoresponse force microscopy