Johannes A. L’huillier

Passively mode-locked picosecond Nd:YVO4 self-Raman laser

We report on a passively mode-locked Nd:YVO4 self-Raman laser which consists of two coupled resonators and generates pulses at 1176nm with a duration of 4.8ps, a repetition rate of 73MHz, and an average power of 420mW.

Terahertz generation in an actively controlled femtosecond enhancement cavity

We report on terahertz generation by Cherenkov-type optical rectification in lithium niobate using an actively controlled femtosecond pumped enhancement cavity. In this way a much higher pump power is available inside the cavity and an increased terahertz output power is obtained. The advantages of terahertz generation in the Cherenkov geometry are verified by comparing it with other types of emitters by means of electro-optical detection as well as by bolometer measurements.

Synchronously pumped femtosecond optical parametric oscillator with integrated sum frequency generation

A synchronously pumped femtosecond optical parametric oscillator (OPO) with intracavity sum frequency generation in a single, periodically poled MgO-doped LiNbO3 (MgO:PPLN) is reported. The used MgO:PPLN crystal contains in series two sections with different poling periods. The first section which generates the 2.5μm OPO idler wave is followed by a second section which generates the sum frequency of the pump and the idler radiation and thus provides at 589nm yellow 140fs long pulses with an average power of up to 190mW. This corresponds to an optical overall conversion efficiency of 15%.

Efficient generation of mode-locked pulses in Nd:YVO 4 with a pulse duration adjustable between 34 ps and 1 ns

We report on the generation of highly stable active continuous mode-locked pulses in diode pumped Nd:YVO(4) with an adjustable pulse duration between 34 ps and 1 ns. With this laser an average output power of up to 7.3 W with an excellent stability and beam quality with a M(2)-value of < 1.1 is obtained. For all pulse durations the pulses were within a factor of 1.15 above the Fourier limit. Due to these characteristics the presented system is an attractive oscillator for OPCPA concepts.

Mode-locking of a high power, 888 nm pumped Nd:YVO 4 laser using nonlinear polarization rotation via Type I second harmonic generation

Continuous-wave mode-locking of a laser exploiting the nonlinear polarization rotation (NPR) technique via Type I second harmonic generation is demonstrated for the first time. The NPR is generated by a lithium triborate crystal and transformed into nonlinear cavity losses of a 888 nm pumped Nd:YVO4 laser. Self-starting, reliable mode-locking has been achieved at a high average output power of 20.6 W and a pulse duration of 7.3 ps. Furthermore, transform limited pulses down to 2.7 ps have been demonstrated at 9.9 W.

Characterization and laser performance of a new material: 2 at. % Nd:YAG grown by the Czochralski method

We report on the optical quality and laser performance of Czochralski-grown 2-at. %-doped Nd:YAG. Using a diode pumped laser in an end pumped configuration, we compare the laser performance of this material with the performance of 1-at. %-doped Nd:YAG and 0.7-at. %-doped Nd:YVO4 crystals. Experimental results show the superior performance of 2-at. % Nd:YAG over Nd:YVO4. With a pump power of 25.7 W, a maximum output power of 12.3 W with a slope efficiency of 57% and an optical-to-optical efficiency of 48% were achieved.

High-power actively Q-switched single-mode 1342 nm Nd:YVO 4 ring laser, injection-locked by a cw single-frequency microchip laser

In this paper we report on the realization of a single-mode Q-switched Nd:YVO4 ring laser at 1342 nm. Unidirectional and single-mode operation of the ring laser is achieved by injection-locking with a continuous wave Nd:YVO4 microchip laser, emitting a single-frequency power of up to 40 mW. The ring laser provides a single-mode power of 13.9 W at 10 kHz pulse repetition frequency with a pulse duration of 18.2 ns and an excellent beam quality (M2 < 1.05). By frequency doubling of the fundamental 1342 nm laser, a power of 8.7 W at 671 nm with a pulse duration of 14.8 ns and a beam propagation factor of M2 < 1.1 is obtained. The 671 nm radiation features a long-term spectral width of 75 MHz.

Impact of the phase-mismatch in the SHG crystal and consequential self-action of the fundamental wave by cascaded second-order effects on the THG efficiency of a Q-switched 1342 nm Nd:YVO 4 laser

We report on the influence of self-focusing and self-defocusing in the phase-mismatched frequency doubling crystal on the third harmonic generation (THG) efficiency in a two crystal frequency tripling scheme. By detuning the temperature of the doubling crystal, the impact of a phase-mismatch in second harmonic generation (SHG) on the subsequent sum frequency mixing process was investigated. It was found that adjusting the temperature not only affected the power ratio of the second harmonic to the fundamental but also the beam diameter of the fundamental beam in the THG crystal, which was caused by self-focusing and self-defocusing of the fundamental beam, respectively. This self-action was induced by a cascaded χ(2) : χ(2) process in the phase-mismatched SHG crystal. Self-defocusing was observable for positive detuning and self-focusing for negative detuning of the phase-matching temperature. Hence, the THG efficiency was not symmetric with respect to the point of optimum phase-matching. Optimum THG was obtained for positive detuning and the resulting self-defocusing in combination with the focusing lens in front of the THG stage was also beneficial for the beam quality of the third harmonic.

5.7 W cw single-frequency laser at 671 nm by single-pass second harmonic generation of a 17.2 W injection-locked 1342 nm Nd : YVO 4 ring laser using periodically poled MgO : LiNbO 3

We demonstrate a continuous wave single-frequency laser at 671.1 nm based on a high-power 888 nm pumped Nd:YVO4 ring laser at 1342.2 nm. Unidirectional operation of the fundamental ring laser is achieved with the injection-locking technique. A Nd:YVO4 microchip laser serves as the injecting seed source, providing a tunable single-frequency power of up to 40 mW. The ring laser emits a single-frequency power of 17.2 W with a Gaussian beam profile and a beam propagation factor of M2<1.1. A 60-mm-long periodically poled MgO-doped LiNbO3 crystal is used to generate the second harmonic in a single-pass scheme. Up to 5.7 W at 671.1 nm with a Gaussian shaped beam profile and a beam propagation factor of M2<1.2 are obtained, which is approximately twice the power of previously reported lasers. This work opens possibilities in cold atoms experiments with lithium, allowing the use of larger ensembles in magneto-optical traps or higher diffraction orders in atomic beam interferometers.

193 fs from an Yb:YAG oscillator mode-locked using nonlinear polarization rotation via Type I SHG with intrinsic dispersion compensation.

The mode-locking technique using nonlinear polarization rotation via Type I second-harmonic generation (SHG) is demonstrated on the femtosecond timescale. The narrow spectral bandwidth of the loss modulation was broadened via a double crystal approach, which allows for mode-locking broadband gain media. We prove the predicted advantages of the technique to be correct utilizing intrinsic dispersion compensation and group-velocity mismatch management to produce 193 fs pulses. This eliminates the need for dispersion compensating elements. The technique can be applied to high-power lasers at any wavelength where a suitable SHG process is possible.