High Repetition Rate Mode-locked Lasers Research Articles

Mode-Locking With Ultra-Low Intra-Cavity Pulse Intensity Using Enhanced Kerr Nonlinearity

Kerr lens mode locking strongly depends upon intensity. Low pulse intensity weakens the nonlinear Kerr lens, and eventually mode locking is not supported. We demonstrate efficient mode-locking in a Ti:Sapphire laser oscillator with record-low intra-cavity pulse intensity (18 GW/cm2) and intra-cavity average power (340 mW). Using an additional nonlinear window in the cavity, the Kerr nonlinearity can be enhanced by an order of magnitude compared to the standard Ti:Sapphire cavity, allowing mode locking with an output coupler reflectivity as low as R = 55% and record-low intra-cavity pulse intensity. Our results provide an important new possibility to control mode-locking in cavities with very low intra-cavity pulse intensity, such as semiconductor laser oscillators and high-repetition rate mode-locked lasers.

Stable, dual mode, high repetition rate mode-locked laser based on a microring resonator

We demonstrate a novel mode locked ultrafast laser, based on an integrated high-Q microring resonator. Our scheme exhibits stable operation of two slightly shifted spectral optical comb replicas. It generates a highly monochromatic radiofrequency modulation of 65.8MHz with a linewidth < 10kHz, on a 200GHz output pulse train.

Broadband graphene electro-optic modulators with sub-wavelength thickness

Graphene's featureless optical absorption, ultrahigh carrier mobility, and variable optical absorption by an applied gate voltage enable a new breed of optical modulators with broad optical and electrical bandwidths. Here we report on an electro-optic modulator that integrates single-layer graphene in a sub-wavelength thick, reflective modulator structure. These modulators provide a large degree of design freedom, which allows tailoring of their optical properties to specific needs. Current devices feature an active aperture ~100 µm, and provide uniform modulation with flat frequency response from 1 Hz to >100 MHz. These novel, low insertion-loss graphene-based modulators offer solutions to a variety of high-speed amplitude modulation tasks that require optical amplitude modulation without phase distortions, a flat frequency response, or ultra-thin geometries, such as for controlling monolithic, high-repetition rate mode-locked lasers or active interferometers.

A Multifrequency Phase Fluorometer Using the Harmonic Content of a Mode-Locked Laser

ABSTRACT We describe the construction and operation of a cross-correlation phase and modulation fluorometer which uses the harmonic content of a high repetition rate mode-locked laser as the excitation source. A mode-locked argon ion laser is used to synchronously pump a dye laser. The pulse train output from the dye laser is amplitude modulated by an acousto-optic modulator and then frequency doubled with an angle tuned frequency doubler. With the particular dye utilized in these studies, the ultraviolet light obtained was continuously tunable over the range 280-310 nm. In the frequency domain the high repetition rate pulsed source gives a large series of equally spaced harmonic frequencies. The frequency spacing of the harmonics is determined by the repetition frequency of the laser. Amplitude modulation of the pulse train permits variation of the frequency quasi-continuously from a few hertz to gigahertz. Use of cross-correlation techniques permits precise isolation of individual frequencies. The cross-correlation frequency required for the analysis of the phase delay and modulation ratio is obtained using coupled frequency synthesizers. In the present instrument three synthesizers are used. One drives the pump mode-locker head, a second drives the acousto-optic modulator and the third is used to modulate the response of the photomultiplier tubes which detect the signal. The accuracy, reproducibility and sensitivity of the instrumentation have been determined. Experimental data are provided to show use of this high frequency cross-correlation phase-modulation fluorometer for the determination of fluorescence lifetimes and rotational motions of tryptophan in solution and in proteins.