We demonstrate a 1 GHz prismless femtosecond Ti:sapphire ring laser which emits 890 mW for 7.6W of pump power over a continuum extending from 585 to 1200 nm at -20 dB below the maximum. A broadband continuum is obtained without careful mirror dispersion compensation, with the net cavity group-delaydispersion having -50 to +100 fs 2 oscillations from 700 to 900 nm. Further broadening is obtained by use of a slightly convex cavity mirror that increases selfphase modulation. 17% (75%) of the intracavity (output) power is generated in single-pass through the crystal, outside the cavity bandwidth and concentrated in the low gain infrared region from 960 to 1200 nm. This laser seems well suited for optical frequency metrology, possibly allowing easier stabilization of the carrier-to-envelope offset frequency without use of photonic fibers.OCIS codes: 140.7090, 320.7160, 120.3940 Femtosecond lasers are the basis of optical frequency combs, which have revolutionized frequency metrology and precision measurements in the recent past years 1 . They have been used, for example, for direct measurements of frequencies of several hundred THz 2 , in optical atomic clocks 3 and for phase-sensitive nonlinear optics experiments 4 . For measurement and control of the carrier-to-envelope offset frequency 1 (f ceo ) in optical frequency combs, a femtosecond laser whose spectrum covers one octave is desirable. Although the use of a microstructure fiber offers a solution to this, there are problems for continuous and long-term operation, which is important for clocks and other applications. In this way, the advent of femtosecond lasers (in particular Ti:sapphire) emitting a broadband continuum 5,6,7,8,9 has attracted interest. These lasers have been demonstrated with stationary-wave, longer cavities operating with prisms in order to compensate for group delay dispersion (GDD), or with short, traveling-wave, prismless ring cavities that use chirped mirrors. In the first case, repetition rates are typically smaller, near 100 MHz or below, while the second case allows for repetition rates of one Gigahertz or higher, which are often preferred for optical frequency measurements. Measurement and stabilization of f ceo has also been demonstrated with such lasers 7,8,9 . In this letter, we report what to our knowledge is the most broadband femtosecond spectrum to date, obtained from a Ti:sapphire laser whose spectrum covers from 585 to 1200 nm at a level of -20 dB below the maximum. It operates stably with an output power of 890 mW for 7.6 W of pump power, and a repetition rate near 1 GHz. We discuss its characterization and the points which we found to be important for stable ultra broadband operation.The main laser cavity described here consists of a 4-mirror bow-tie ring cavity comprising two curved mirrors (including the input coupler (IC)), with broadband high reflecting (HR) coatings and radius of curvature of 3 cm, a HR flat mirror and a flat output coupler (OC) with a transmission of 2 % from 730 to 870 nm. All mirrors are commercia...

We report on the combined action of a cw diode laser and a train of ultrashort pulses when each of them drives one step of the 5S-5P-5D two-photon transition in rubidium vapor. The fluorescence from the 6P(3/2) state is detected for a fixed repetition rate of the femtosecond laser while the cw-laser frequency is scanned over the rubidium D(2) lines. This scheme allows for a velocity selective spectroscopy in a large spectral range including the 5D(3/2) and 5D(5/2) states. The results are well described in a simplified frequency domain picture, considering the interaction of each velocity group with the cw laser and a single mode of the frequency comb.

We report a self-starting prismless femtosecond Ti:sapphire ring laser whose repetition rate has been gradually increased from 1 to 2.12 GHz. A broadband spectrum extending from 650 to 1040 nm, in which 17% of the intracavity power is generated in a single-pass through the crystal, is preserved in spite of the reduction in peak power. An average power of 0.95 W was obtained for 7.5 W of pump power, with very stable operation verified over 22 hours. Pulses from this laser have been fully characterized in spectral phase, and then compressed to 5.9 femtoseconds using multiphoton intrapulse interference phase scan (MIIPS).

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We consider two long resistive straight parallel wires carrying opposite constant currents and calculate the potential and electric field everywhere in space and the surface charge densities along the wires. The problem is solved through Laplace’s equation in bi-cylinder coordinates, far from the battery. We compare these calculations with previous known results that used different methods. We also calculate the numerical solution for the case in which the battery is present, and show the equipotentials and surface charges close to the battery.