## 1 Introduction  
The ultrashort pulse lasers of infrared (IR) light have gained great attentions for ophthalmic, surgical, dental, therapeutic, and aesthetic medical applications. The pulses from the picosecond (ps) to femtosecond (fs) require less energy to ablate biological tissues and the accuracy is in the micrometer range. At the micrometer point of the tissue through which the ultrashort pulse passes, tiny harmless carbon dioxide and water vapor bubbles are generated. Solid-state diode laser offers a number of advantages over conventional laser sources, such as reduced power consumption, better spectral purity, increased lifetime and low costs, all of which are continuously improving. It is the best and only way to promote a new high-technology development on ultrafast diode lasers. The fabrications of group II-VI laser-diodes (LDs) have become quite important for ultra-short coherent light sources. Divalent chromium doped lasers of the II-VI family emitting in the mid-infrared (mid-IR) (2-3 um) have recently matured to the commercial continuous-wave lasers. The passively mode-locked femtosecond Cr\({}^{2+}\):ZnSe laser was first reported in 2006, generating \(\sim\)100 fs pulses at up to 75 mW power around 2.5 um wavelength [1]. The first Kerr-lens mode-locked (KLM-locked) Cr\({}^{2+}\):ZnSe laser has two distinct regimes. In the first, the output power and duration of the high-power soliton regime of Cr\({}^{2+}\):ZnSe laser is about 300 mW and 100 fs, respectively. In contrast, the output power and pulse duration of the chirped pulse regime of Cr\({}^{2+}\):ZnSe laser is about 170 mW and 1 ps, respectively [2]. In addition, another KLM-locked Cr\({}^{2+}\):ZnSe can generate 95 fs pulses with an output power as high as 40 mW around 2420 nm wavelength [3]. Furthermore, the first chirped-mirror dispersion controlled KLM Cr\({}^{2+}\):ZnSe laser using a semiconductor saturable absorbing mirror (SESAM) can generate nearly transform-limited 80 fs pulses at 80 mW output power around 2.4 um wavelength [4]. On the other hand, Cr\({}^{2+}\):ZnS lasers have been extensively studied both experimentally and theoretically. The zinc-blende ZnS has the larger band gap of 3.8 eV, higher thermal conductivity of 27 W/mK, higher thermal shock parameter of 7.1 W/m\({}^{1/2}\), and lower \(d\)n/\(dT\) of \(46\times 10^{-6}\) K\({}^{-1}\), compared respectively to 2.8 eV, 18 W/mK, 5.3 W/m\({}^{1/2}\), and 70 \(\times\) 10\({}^{-6}\) K\({}^{-1}\) in ZnSe [5; 6]. Therefore, the fabrication of Cr\({}^{2+}\):ZnS lasers has shown the promising prospect for high-power applications. The first continuous-wave (CW) tunable Cr\({}^{2+}\):ZnS laser was first introduced using the direct diode-pumping at 1.67 \(\upmu\)m and generating 100 mW output power of the broadly CW tunable over \(\sim\)280 nm around 2.3 \(\upmu\)m wavelength [7]. Furthermore, the first mode-locked CW Cr\({}^{2+}\):ZnS laser, passively mode-locked by a multiple quantum well InAs/GaSb based SESAM, generated \(\sim\)1.1 ps pulses at 125 mW of output power around 2.45 \(\upmu\)m [8]. Recently, the first single-crystalline KLM femtosecond Cr\({}^{2+}\):ZnS laser was reported, generating high power up to 200 mW stable around 2.4 \(\upmu\)m wavelength and clean 110 fs pulses at 180 MHz repetition rate [9]. To date, output average power up to 800 mW at 49.9 MHz repetition rate, and pulse duration as short as 34 fs at 2.4 \(\upmu\)m wavelength have been determined experimentally using the KLM-locked femtosecond Cr\({}^{2+}\):ZnS oscillator pumped by two single-emitter InP C-Mount laser diodes [10]. Due to promising unique properties advanced Cr\({}^{2+}\) doped II-VI materials for medical lasers have attracted tremendous recent attention from both fundamental and practical viewpoints and their applications have become a hot and active field in the world range wide. In recent applications, the ZnTe crystal shows attractive detection performances at frequencies below the Reststrahlen band (\(<\)5.3 THz for ZnTe) with a broadband (FWHM = 100 nm) femtosecond (fs) laser [11].