Christoph Becher - Academia.edu (original) (raw)
Papers by Christoph Becher
Procedia Engineering, 2004
ABSTRACT
We design photonic crystal microcavities in diamond films for applications in quantum information... more We design photonic crystal microcavities in diamond films for applications in quantum information yielding high quality factors Q>66000 and small mode volume Vap1.1(lambda/n)3. The calculated quality factors show a strong dependence on material absorption.
Foot and Ankle Surgery, 2006
A case of an osteochondral defect of the second metatarsal head treated with autogenous osteochon... more A case of an osteochondral defect of the second metatarsal head treated with autogenous osteochondral transplantation from the talonavicular joint is presented. At 6-months follow-up, the patient had returned to previous activities with no complaints. MRI evaluation showed good congruency of the joint surface and complete incorporation of the osteochondral autograft.
We present, characterize, and apply a photonic quantum interface between the near infrared and te... more We present, characterize, and apply a photonic quantum interface between the near infrared and telecom spectral regions. A singly resonant optical parametric oscillator (OPO) operated below threshold, in combination with external filters, generates high-rate ($>2.5\cdot10^6~{\rm s}^{-1}$) narrowband photon pairs ($\sim 7$ MHz bandwidth); the signal photons are tuned to resonance with an atomic transition in Ca$^+$, while the idler photons are at telecom wavelength. Quantum interface operation is demonstrated through high-rate absorption of single photons by a single trapped ion ($\sim 670~{\rm s}^{-1}$), heralded by coincident telecom photons.
We report on the self-guided operation of a singly resonant, thermally loaded CW OPO and its impr... more We report on the self-guided operation of a singly resonant, thermally loaded CW OPO and its improved characteristics of mode quality and stability in the case of a MgO:PPLN crystal pumped at 532 nm.
Proceedings of 1994 Nonlinear Optics: Materials, Fundamentals and Applications
A detailed characterization of this KTiOPO4 optical parametric oscillator (OPO) system and its sp... more A detailed characterization of this KTiOPO4 optical parametric oscillator (OPO) system and its spectral properties will be presented, including investigations which use the radiation of an injection-locked 1W, 764nm diode laser array as pump source
We introduce a process for the fabrication of high quality, spatially isolated nano-diamonds on i... more We introduce a process for the fabrication of high quality, spatially isolated nano-diamonds on iridium via microwave plasma assisted CVD-growth. We perform spectroscopy of single silicon-vacancy (SiV)-centres produced during the growth of the nano-diamonds. The colour centres exhibit extraordinary narrow zero-phonon-lines down to 0.7 nm at room temperature. Single photon count rates up to 4.8 Mcps at saturation make these
Conference on Lasers and Electro-Optics 2010, 2010
1Department of Physics, Pusan National University, Busan 609-735, Rep. Korea 2Universität des Saa... more 1Department of Physics, Pusan National University, Busan 609-735, Rep. Korea 2Universität des Saarlandes, Fachrichtung 7.3 (Technische Physik), 66123 Saarbrücken, Germany 3Division of Physical Metrology, Korea Research Institute of Standards and Science (KRISS), ...
Conference on Lasers and Electro-Optics/International Quantum Electronics Conference and Photonic Applications Systems Technologies, 2004
We measure the spontaneous emission lifetime of the D5/2 level of a single Ca+-ion by pii-pulse e... more We measure the spontaneous emission lifetime of the D5/2 level of a single Ca+-ion by pii-pulse excitation and quantum state detection. As the trapped ion is well localized we map the standing-wave cavity vacuum field
Physical Realizations of Quantum Computing - Are the DiVincenzo Criteria Fulfilled in 2004?, 2006
We present a series of experiments where up to three ions held in a Paul trap are entangled, a gi... more We present a series of experiments where up to three ions held in a Paul trap are entangled, a given number of ions is selectively read out while conditional singlequantum-bit (qubit) operations are performed coherently on the remaining ion(s). Using these techniques, we demonstrate also a state transfer of a quantum bit from one ion to another one using two measurements and entanglement between an auxiliary ion and the target ion-also known as teleportation.
Techniques in Foot & Ankle Surgery, 2004
Cheilectomy is an established method for the treatment of hallux rigidus. In a prospective study,... more Cheilectomy is an established method for the treatment of hallux rigidus. In a prospective study, dorsal cheilectomy combined with an extensive plantar release and microfracture technique was performed in 36 patients with 37 cases of hallux rigidus. Patients were rated using the American Orthopaedic Foot & Ankle Society Metatarsophalangeal-Interphalangeal Score and a visual analogue score. Preoperative radiographs showed 25 cases of grade 2 and 12 cases of grade 3. Score results improved significantly from 43 points preoperatively to 78 points (range 35-100 points), both after 1 and 2 years postoperatively. The outcome of the Visual Analogue Score after 2 years was 7.1 for pain (preoperative: 2.2; 1 year: 7.0), 7.1 for function (preoperative: 2.8; 1 year: 6.7), and 7.4 for satisfaction (preoperative: 1.1; 1 year: 6.6). Clinical examination showed an average improvement in range of motion of 22°. Patients classified as grade 3 were found to have poorer results than grade 2. The described technique has proven to be an effective method to relieve pain and improve function. However, longer-term results remain to be evaluated.
Operative Techniques in Orthopaedics, 2014
The treatment of osteochondral defects of the talus is still controversial. Matrix-guided treatme... more The treatment of osteochondral defects of the talus is still controversial. Matrix-guided treatment options for covering of the defect with a scaffold have gained increasing popularity. Cellular-based autologous chondrocyte implantation (ACI) has undergone a generational development overcoming the surgical drawbacks related to the use of the periosteal flap over time. As ACI is associated with high costs and limited in availability, autologous matrix-induced chondrogenesis, a single-step procedure combining microfracturing of the subchondral bone to release bone marrow mesenchymal stem cells in combination with the coverage of an acellular matrix, has gained increasing popularity. The purposes of this report are to present the arthroscopic approach of the matrix-guided autologous matrix-induced chondrogenesis technique and generational development of ACI in the treatment of chondral and osteochondral defects of the talus.
Conference on Lasers and Electro-Optics/International Quantum Electronics Conference and Photonic Applications Systems Technologies, 2004
We measure the spontaneous emission lifetime of the D5/2 level of a single Ca+-ion by Pi-pulse ex... more We measure the spontaneous emission lifetime of the D5/2 level of a single Ca+-ion by Pi-pulse excitation and quantum state detection. As the trapped ion is well localized we map the standing-wave cavity vacuum field.
Foot & ankle international, 2005
The microfracture technique has been used successfully for the treatment of cartilage defects in ... more The microfracture technique has been used successfully for the treatment of cartilage defects in the knee. The purpose of this study was to evaluate the microfracture technique in the treatment of osteochondral and degenerative chondral defects of the talus. In a prospective study, 30 ankles in 30 consecutive patients (17 men and 13 women; average age, 41 years; range 20 to 74 years were treated with arthroscopic microfracture. Twenty patients had osteochondral defects and 10 had degenerative chondral defects. Patients were evaluated with clinical examination and MRI preoperatively and at 3, 6, 12, and 24 months postoperatively. At a mean followup of 2 years (range 22 to 27 months), 29 patients were available for follow-up. The results for all ankles according to the Hannover Scoring System were 45% excellent, 38% good, and 17% satisfactory. Results in patients older than 50 years were not inferior to those in younger patients. Visual Analog Score revealed an average of 8 +/- 2 for ...
Conference on Lasers and Electro-Optics 2010, 2010
ABSTRACT We report on a diode laser pumped continuous wave, pump enhanced idler-resonant optical ... more ABSTRACT We report on a diode laser pumped continuous wave, pump enhanced idler-resonant optical parametric oscillator. Cavity stabilization by a Pound-Drever-Hall scheme using direct modulation of the diode laser enables long-time frequency and amplitude stable output.
Nonlinear Optics, 2011
ABSTRACT We report on quantum frequency downconversion using a ZnO:PPLN ridge waveguide. An inter... more ABSTRACT We report on quantum frequency downconversion using a ZnO:PPLN ridge waveguide. An internal conversion efficiency of 73% is achieved. We identify Raman scattering to be the dominant noise source in the frequency converter.
Conference on Lasers and Electro-Optics 2010, 2010
We propose a practical implementation for single-photon down conversion based on difference frequ... more We propose a practical implementation for single-photon down conversion based on difference frequency generation by a nonlinear crystal. A theoretical model is presented, where the quantum noise sources, relevant to the process, are identified.
Conference Digest. 2000 Conference on Lasers and Electro-Optics Europe (Cat. No.00TH8505), 2000
ABSTRACT Summary form only given. We give an overview on selected examples of diode pumped OPOs. ... more ABSTRACT Summary form only given. We give an overview on selected examples of diode pumped OPOs. We report on diode pumped triply and doubly-resonant CW OPOs with low threshold powers in the range of about 100 μW to 100 mW. Such OPOs are of interest, e.g. for a phase-coherent all-optical frequency division, such as in a self-phase-locked degenerate OPO. We present an all-optical frequency-by-3 divider, where a two-section PPLN crystal enables operation of the OPO simultaneously with intracavity frequency doubling of the idler wave, for an optical phase-locking of the signal wave at twice the idler frequency. The OPO converts the 812 nm wavelength of an AlGaAs diode laser into a signal wavelength of 1218 nm and an idler wavelength of 2436 nm, where these wavelengths are exact (integer) multiples of the pump wavelength. At higher diode pump powers, such as provided by MOPA systems, it becomes possible to operate singly-resonant CW-OPOs (SROs) well above threshold. We describe a signal-resonant ring-cavity SRO which is based on PPLN and is pumped with an InGaAs diode MOPA system at wavelengths around 925 nm. The SRO shows a threshold of 1.6 W whereas the single-frequency maximum 2.07 μm idler output power is 0.5 W at a pump power of 2.5 W. Coarse and quick tuning across hundreds of nanometers is achieved by tuning the diode laser over an interval of 1.5 nm. More than 50 GHz continuous (mode-hop free) tuning of the idler wave is possible by continuous tuning of the diode laser wavelength
Procedia Engineering, 2004
ABSTRACT
We design photonic crystal microcavities in diamond films for applications in quantum information... more We design photonic crystal microcavities in diamond films for applications in quantum information yielding high quality factors Q>66000 and small mode volume Vap1.1(lambda/n)3. The calculated quality factors show a strong dependence on material absorption.
Foot and Ankle Surgery, 2006
A case of an osteochondral defect of the second metatarsal head treated with autogenous osteochon... more A case of an osteochondral defect of the second metatarsal head treated with autogenous osteochondral transplantation from the talonavicular joint is presented. At 6-months follow-up, the patient had returned to previous activities with no complaints. MRI evaluation showed good congruency of the joint surface and complete incorporation of the osteochondral autograft.
We present, characterize, and apply a photonic quantum interface between the near infrared and te... more We present, characterize, and apply a photonic quantum interface between the near infrared and telecom spectral regions. A singly resonant optical parametric oscillator (OPO) operated below threshold, in combination with external filters, generates high-rate ($>2.5\cdot10^6~{\rm s}^{-1}$) narrowband photon pairs ($\sim 7$ MHz bandwidth); the signal photons are tuned to resonance with an atomic transition in Ca$^+$, while the idler photons are at telecom wavelength. Quantum interface operation is demonstrated through high-rate absorption of single photons by a single trapped ion ($\sim 670~{\rm s}^{-1}$), heralded by coincident telecom photons.
We report on the self-guided operation of a singly resonant, thermally loaded CW OPO and its impr... more We report on the self-guided operation of a singly resonant, thermally loaded CW OPO and its improved characteristics of mode quality and stability in the case of a MgO:PPLN crystal pumped at 532 nm.
Proceedings of 1994 Nonlinear Optics: Materials, Fundamentals and Applications
A detailed characterization of this KTiOPO4 optical parametric oscillator (OPO) system and its sp... more A detailed characterization of this KTiOPO4 optical parametric oscillator (OPO) system and its spectral properties will be presented, including investigations which use the radiation of an injection-locked 1W, 764nm diode laser array as pump source
We introduce a process for the fabrication of high quality, spatially isolated nano-diamonds on i... more We introduce a process for the fabrication of high quality, spatially isolated nano-diamonds on iridium via microwave plasma assisted CVD-growth. We perform spectroscopy of single silicon-vacancy (SiV)-centres produced during the growth of the nano-diamonds. The colour centres exhibit extraordinary narrow zero-phonon-lines down to 0.7 nm at room temperature. Single photon count rates up to 4.8 Mcps at saturation make these
Conference on Lasers and Electro-Optics 2010, 2010
1Department of Physics, Pusan National University, Busan 609-735, Rep. Korea 2Universität des Saa... more 1Department of Physics, Pusan National University, Busan 609-735, Rep. Korea 2Universität des Saarlandes, Fachrichtung 7.3 (Technische Physik), 66123 Saarbrücken, Germany 3Division of Physical Metrology, Korea Research Institute of Standards and Science (KRISS), ...
Conference on Lasers and Electro-Optics/International Quantum Electronics Conference and Photonic Applications Systems Technologies, 2004
We measure the spontaneous emission lifetime of the D5/2 level of a single Ca+-ion by pii-pulse e... more We measure the spontaneous emission lifetime of the D5/2 level of a single Ca+-ion by pii-pulse excitation and quantum state detection. As the trapped ion is well localized we map the standing-wave cavity vacuum field
Physical Realizations of Quantum Computing - Are the DiVincenzo Criteria Fulfilled in 2004?, 2006
We present a series of experiments where up to three ions held in a Paul trap are entangled, a gi... more We present a series of experiments where up to three ions held in a Paul trap are entangled, a given number of ions is selectively read out while conditional singlequantum-bit (qubit) operations are performed coherently on the remaining ion(s). Using these techniques, we demonstrate also a state transfer of a quantum bit from one ion to another one using two measurements and entanglement between an auxiliary ion and the target ion-also known as teleportation.
Techniques in Foot & Ankle Surgery, 2004
Cheilectomy is an established method for the treatment of hallux rigidus. In a prospective study,... more Cheilectomy is an established method for the treatment of hallux rigidus. In a prospective study, dorsal cheilectomy combined with an extensive plantar release and microfracture technique was performed in 36 patients with 37 cases of hallux rigidus. Patients were rated using the American Orthopaedic Foot & Ankle Society Metatarsophalangeal-Interphalangeal Score and a visual analogue score. Preoperative radiographs showed 25 cases of grade 2 and 12 cases of grade 3. Score results improved significantly from 43 points preoperatively to 78 points (range 35-100 points), both after 1 and 2 years postoperatively. The outcome of the Visual Analogue Score after 2 years was 7.1 for pain (preoperative: 2.2; 1 year: 7.0), 7.1 for function (preoperative: 2.8; 1 year: 6.7), and 7.4 for satisfaction (preoperative: 1.1; 1 year: 6.6). Clinical examination showed an average improvement in range of motion of 22°. Patients classified as grade 3 were found to have poorer results than grade 2. The described technique has proven to be an effective method to relieve pain and improve function. However, longer-term results remain to be evaluated.
Operative Techniques in Orthopaedics, 2014
The treatment of osteochondral defects of the talus is still controversial. Matrix-guided treatme... more The treatment of osteochondral defects of the talus is still controversial. Matrix-guided treatment options for covering of the defect with a scaffold have gained increasing popularity. Cellular-based autologous chondrocyte implantation (ACI) has undergone a generational development overcoming the surgical drawbacks related to the use of the periosteal flap over time. As ACI is associated with high costs and limited in availability, autologous matrix-induced chondrogenesis, a single-step procedure combining microfracturing of the subchondral bone to release bone marrow mesenchymal stem cells in combination with the coverage of an acellular matrix, has gained increasing popularity. The purposes of this report are to present the arthroscopic approach of the matrix-guided autologous matrix-induced chondrogenesis technique and generational development of ACI in the treatment of chondral and osteochondral defects of the talus.
Conference on Lasers and Electro-Optics/International Quantum Electronics Conference and Photonic Applications Systems Technologies, 2004
We measure the spontaneous emission lifetime of the D5/2 level of a single Ca+-ion by Pi-pulse ex... more We measure the spontaneous emission lifetime of the D5/2 level of a single Ca+-ion by Pi-pulse excitation and quantum state detection. As the trapped ion is well localized we map the standing-wave cavity vacuum field.
Foot & ankle international, 2005
The microfracture technique has been used successfully for the treatment of cartilage defects in ... more The microfracture technique has been used successfully for the treatment of cartilage defects in the knee. The purpose of this study was to evaluate the microfracture technique in the treatment of osteochondral and degenerative chondral defects of the talus. In a prospective study, 30 ankles in 30 consecutive patients (17 men and 13 women; average age, 41 years; range 20 to 74 years were treated with arthroscopic microfracture. Twenty patients had osteochondral defects and 10 had degenerative chondral defects. Patients were evaluated with clinical examination and MRI preoperatively and at 3, 6, 12, and 24 months postoperatively. At a mean followup of 2 years (range 22 to 27 months), 29 patients were available for follow-up. The results for all ankles according to the Hannover Scoring System were 45% excellent, 38% good, and 17% satisfactory. Results in patients older than 50 years were not inferior to those in younger patients. Visual Analog Score revealed an average of 8 +/- 2 for ...
Conference on Lasers and Electro-Optics 2010, 2010
ABSTRACT We report on a diode laser pumped continuous wave, pump enhanced idler-resonant optical ... more ABSTRACT We report on a diode laser pumped continuous wave, pump enhanced idler-resonant optical parametric oscillator. Cavity stabilization by a Pound-Drever-Hall scheme using direct modulation of the diode laser enables long-time frequency and amplitude stable output.
Nonlinear Optics, 2011
ABSTRACT We report on quantum frequency downconversion using a ZnO:PPLN ridge waveguide. An inter... more ABSTRACT We report on quantum frequency downconversion using a ZnO:PPLN ridge waveguide. An internal conversion efficiency of 73% is achieved. We identify Raman scattering to be the dominant noise source in the frequency converter.
Conference on Lasers and Electro-Optics 2010, 2010
We propose a practical implementation for single-photon down conversion based on difference frequ... more We propose a practical implementation for single-photon down conversion based on difference frequency generation by a nonlinear crystal. A theoretical model is presented, where the quantum noise sources, relevant to the process, are identified.
Conference Digest. 2000 Conference on Lasers and Electro-Optics Europe (Cat. No.00TH8505), 2000
ABSTRACT Summary form only given. We give an overview on selected examples of diode pumped OPOs. ... more ABSTRACT Summary form only given. We give an overview on selected examples of diode pumped OPOs. We report on diode pumped triply and doubly-resonant CW OPOs with low threshold powers in the range of about 100 μW to 100 mW. Such OPOs are of interest, e.g. for a phase-coherent all-optical frequency division, such as in a self-phase-locked degenerate OPO. We present an all-optical frequency-by-3 divider, where a two-section PPLN crystal enables operation of the OPO simultaneously with intracavity frequency doubling of the idler wave, for an optical phase-locking of the signal wave at twice the idler frequency. The OPO converts the 812 nm wavelength of an AlGaAs diode laser into a signal wavelength of 1218 nm and an idler wavelength of 2436 nm, where these wavelengths are exact (integer) multiples of the pump wavelength. At higher diode pump powers, such as provided by MOPA systems, it becomes possible to operate singly-resonant CW-OPOs (SROs) well above threshold. We describe a signal-resonant ring-cavity SRO which is based on PPLN and is pumped with an InGaAs diode MOPA system at wavelengths around 925 nm. The SRO shows a threshold of 1.6 W whereas the single-frequency maximum 2.07 μm idler output power is 0.5 W at a pump power of 2.5 W. Coarse and quick tuning across hundreds of nanometers is achieved by tuning the diode laser over an interval of 1.5 nm. More than 50 GHz continuous (mode-hop free) tuning of the idler wave is possible by continuous tuning of the diode laser wavelength