Tightly locked optical frequency comb from a semiconductor disk laser.

Ultrafast semiconductor disk lasers (SDLs) passively modelocked using semiconductor saturable absorbers mirrors (SESAMs) generate optical frequency combs (OFCs) with gigahertz line spacings - a regime where solid-state and fiber lasers struggle with geometrical and Q-switching limitations. We stabilized both the frequency comb spacing and the offset without any additional external optical amplification or pulse compression. The overall noise performance is competitive with other gigahertz OFCs. A SESAM-modelocked vertical external-cavity surface-emitting laser (VECSEL) at a center wavelength around 1 µm generates 122-fs pulses with 160 mW average output power and we only needed 17-pJ pulse energy coupled into a silicon nitride (Si3N4) waveguide for supercontinuum generation (SCG) and OFC offset stabilization.

Frequency comb offset detection using supercontinuum generation in silicon nitride waveguides.

We present the first direct carrier-envelope-offset (CEO) frequency detection of a modelocked laser based on supercontinuum generation (SCG) in a CMOS-compatible silicon nitride (Si(3)N(4)) waveguide. With a coherent supercontinuum spanning more than 1.5 octaves from visible to beyond telecommunication wavelengths, we achieve self-referencing of SESAM modelocked diode-pumped Yb:CALGO lasers using standard f-to-2f interferometry. We directly obtain without amplification strong CEO beat signals for both a 100-MHz and 1-GHz pulse repetition rate laser. High signal-to-noise ratios (SNR) of > 25 dB and even > 30 dB have been generated with only 30 pJ and 36 pJ of coupled pulse energy from the megahertz and gigahertz laser respectively. We compare these results to self-referencing using a commercial photonic crystal fiber and find that the required peak power for CEO beat detection with a comparable SNR is lowered by more than an order of magnitude when using a Si(3)N(4) waveguide.

[Injuries and posttraumatic osteoarthritis of the first carpometacarpal joint]. / Verletzungen des Sattelgelenks und posttraumatische Rhizarthrose.

BACKGROUND: Precise function of the hand is crucially characterized by opposition movement of the thumb, only possible because of the functional anatomy of the first carpometacarpal joint. High functional demands to this joint consequently lead to the highest rate of osteoarthritis of the hand joints and loss of function. Carpometacarpal (CMC) osteoarthritis of the thumb is rarely seen in posttraumatic cases. It can be caused by fractures involving the joint surfaces of both, the trapezium or the first metacarpal, whereas dislocations of the carpometacarpal joint itself only occasionally lead to osteoarthritis. OBJECTIVES: Identification and compilation of current concepts in diagnosis and therapy of posttraumatic carpometacarpal osteoarthritis of the thumb. METHODS: Selective PubMed and Cochrane review, data obtained from own patient investigations and author's experiences were used. RESULTS: Adequate treatment of the injury will minimize the risk for future malfunction. In early stages, arthroscopy is a valuable method for the diagnosis and treatment of posttraumatic rhizarthrosis. For all stages, a multitude of operative procedures are described and being used but yet not finally assessed for effectiveness. Advanced osteoarthritis of the first CMC joint is widely treated by trapeziectomy, which is suitable for most patients, and considered as gold standard. Additional procedures like suspension, interposition or k-wire transfixation do not provide any significant advantage and lead to comparable results. It is advisable to treat hyperextension of the metacarpophalangeal joint of the thumb at any stage of CMC osteoarthritis.

SESAM modelocked Yb:CaGdAlO4 laser in the soliton modelocking regime with positive intracavity dispersion.

We demonstrate femtosecond SESAM modelocking in the near-infrared by using cascaded quadratic nonlinearities (phase-mismatched second-harmonic generation, SHG), enabling soliton modelocking in the normal dispersion regime without any dispersion compensating elements. To obtain large and negative self-phase modulation (SPM) we use an intracavity LBO crystal, whose temperature and angles are optimized with respect to SPM, nonlinear losses, and self-starting characteristics. To support femtosecond pulses, we use the very promising Yb:CaGdAlO(4) (CALGO) gain material, operated in a bulk configuration. The LBO crystal provides sufficient negative SPM to compensate for its own GDD as well as the positive GDD and SPM from the gain crystal. The modelocked laser produces pulses of 114 fs at 1050 nm, with a repetition rate of 113 MHz (average output power 1.1 W). We perform a detailed theoretical study of this soliton modelocking regime with positive GDD, which clearly indicates the important design constraints in an intuitive and systematic way. In particular, due to its importance in avoiding multi-pulsed modelocking, we examine the nonlinear loss associated with the cascading process carefully and show how it can be suppressed in practice. With this modelocking regime, it should be possible to overcome the limits faced by current state of the art modelocked lasers in terms of dispersion compensation and nonlinearity management at high powers, suppression of Q-switching in compact GHz lasers, and enabling femtosecond soliton modelocking at very high repetition rates due to the high nonlinearities accessible via cascading combined with eliminating the need for intracavity dispersion compensation.