Passive mode-locking of a diode-pumped Nd:YVO_4 laser by intracavity SHG in PPKTP

Abstract

Experimental results on passive mode-locking of a Nd:YVO(4) laser using intracavity frequency doubling in periodically poled KTP (PPKTP) crystal are reported. Both, negative cascaded chi((2)) lensing and frequency doubling nonlinear mirror (FDNLM) are exploited for the laser mode-locking. The FDNLM based on intensity dependent reflection in the laser cavity ensures self-starting and self-sustaining mode-locking while the cascaded chi((2)) lens process contributes to substantial pulse shortening. This hybrid technique enables generation of stable trains of pulses at high-average output power with several picoseconds pulse width. The pulse repetition rate of the laser is 117 MHz with average output power ranging from 0.5 to 3.1 W and pulse duration from 2.9 to 5.2 ps.

χ(2)-Lens Mode-Locking of a Nd:YVO4 Laser with High Average Power and Repetition Rate up to 600 MHz

“…The average power in ML is close to the maximum achievable in continuous-wave (CW) operation. This behavior is typical for χ (2) -lens mode-locked lasers [4,5]. The pulse duration (FWHM) is 6.1 ps, derived from the measured autocorrelation curve, assuming sech 2 -pulse shape (Fig.…”

“…Moreover, the residual absorption of SESAMs can lead to heating or thermal damage of the absorber, especially for operation at high intra-cavity power and high repetition rate. As an alternative to SESAMs, χ (2) -lens mode-locking has been demonstrated with Nd:YVO 4 and Nd:GdVO 4 lasers emitting output power of several watts with transform-limited pulses [4,5]. In rhis technique two physical processes govern the mode-locking operation: resonator intensity dependent loses due to intra-cavity χ (2) -lens formation and soliton-like pulse shaping due to negative intra-cavity self-phase modulation introduced by phase mismatched SHG.…”

Nd:YVO_4 amplifier for ultrafast low-power lasers

“…The shortest pulses reported for an Nd:YVO 4 oscillator were 2.9 ps long at 0.5 W output power, employing cascaded χ 2 ∶χ 2 nonlinearity [9], whereas the pulse width increases (≈ 5 ps) at higher power levels (3 to 11 W) [9][10][11].…”

Diode-pumped 1988-nm Tm:YAP laser mode-locked by intracavity second-harmonic generation in periodically poled LiNbO_3

“…A FDNLM can provide a low self-starting threshold but has the disadvantage of longer pulse duration due to group velocity mismatch (GVM). The second mechanism is cascaded second-order nonlinear mode locking (CSM), which has a relatively high self-starting threshold, but it contributes substantially to pulse shortening, and can help to achieve continuous-wave mode locking (CWML) [23][24][25][26]. In both schemes, the frequency-doubling crystal can be either birefringence-phase-matching materials or quasi-phase-matching (QPM) ones.…”