Active and passive mode-locking of the Cr2+:ZnSe laser

Abstract

We report purely active mode-locking of Cr 2+ :ZnSe laser with 15-30 ps pulses as well as acousto-optically initiated passive mode-locking with ~4ps pulses at up to 400 mW of output power. Pulse-break-up is observed at intracavity peak-powers exceeding ^50 kW.

Laser crystals and ceramics: recent advances

“…The Cr 2+ ion is the latest TM lasant activator to be used in crystals [227]. Among several known laser crystals containing these 3d 4 ions ( Table 9) the most promising for obtaining broadly tunable and ultra-short-pulsed generation in the mid-IR with LD pumping is ZnSe:Cr 2+ [53,234,235].…”

Multipulse operation and limits of the Kerr-lens mode-locking stability

“…where the different steps within the full cavity round trip describe: 1) the self-phase modulation action (1), where is the field intensity, (here, and are the nonlinear and linear refraction indices, respectively, is the double length of the active medium, and is the central oscillation wavelength); 2) the Kerr-lens induced fast saturable absorber action defining the self-amplitude modulation of the field, is the modulation depth, is the inverse intensity of the loss saturation (2); note that consideration of the strong modulation is necessary in our case owing to the low critical self-focusing power in ZnSe, which is only 0.2 MW [26] as a result of the large value of ; 3) the spectral filter action with the inverse bandwidth , which coincides with the gain bandwidth, is the field carrier frequency coinciding with the minimum of the spectral loss (3); 4) the homogeneously saturated gain and the output loss action with coefficients and , respectively (4); 5) the net-GDD action with the dispersion coefficient where is the linear phase retardation of the field (5). The full round trip results from setting .…”

“…This generic scheme is suitable to model practically all the published experimental studies of multipulsing in Kerr-lens mode-locked lasers in different active media [1], [13], [14], [19], [20], [22], [23], [26]. While our main interest stays with the case of the Cr:ZnSe laser [26], we also consider the Kerr-lens mode-locked Ti:Sapphire laser to verify our model.…”

“…The stable multipulse operation in the negative GDD region was experimentally observed in Ti:sapphire [1], [19]- [21], Cr:LiSGaF [22] and Yb:KYW [23] Kerr-lens mode-locked lasers as well as in Nd:glass [24], Ti:sapphire [4], and Cr :YAG [25] lasers mode locked by a semiconductor saturable absorber mirror. In [26], the tendency toward multipulse generation was reported for the positive-GDD regime in the Cr :ZnSe laser with passive mode locking initiated by acousto-optical modulation.…”

“…At this moment, a variety of generation regimes have been demonstrated: the efficient pulsed [29] and CW [30], diode-pumped operation [31], active mode locking [32], and the active modulator-assisted passive mode locking [26]. Above all, Cr :ZnSe is of interest as the model object for the study of multiple-pulse operation.…”