A diode-pumped bulk Er3+: Yb3+: glass laser has been passively CW modelocked for the first time. Reliable, self-starting passive modelocking using semiconductor saturable absorber mirrors (SESAMs) is demonstrated, with pulses as short as 2.5 ps being obtained with an average output power of 68mW at the telecommunications wavelength of~ 1.5µm.

There has been growing interest in compact lasers producing picosecond pulses at the telecommunications wavelength around 1.5µm. Many applications require a clean train of pulses in the picosecond regime with pulse repetition rates not necessarily in the multi-gigahertz regime. Examples are measurements of the time response of optical switches and detectors, or material investigations for semiconductor optical amplifiers in all-optical switches. Currently mainly Cr4+: YAG and Er3+: Yb3+: glass are used as gain material for pulsed bulk lasers around 1.5µm. Cr4+: YAG has been passively modelocked by Kerr lens modelocking (KLM)[4] or by semiconductor saturable absorber mirrors [2]. However, this laser requires a high-brightness multi-Watt pump because of its weak absorption and high laser threshold. Er3+: Yb3+: glass is a quasi-threelevel gain material which can easily be diode-pumped, because codoping with ytterbium facilitates an efficient pump process around 980nm without increasing the reabsorption losses [3]. Actively modelocked operation of a bulk Er3+: Yb3+: glass laser has been demonstrated [4] producing 9.6 ps at 3mW output power. Passively modelocked erbium-doped fiber lasers have been shown to produce sub-picosecond pulses with nanojoule pulse energies using different approaches [5, 6]. However, the pulses of the sideand cladding-pumped erbium laser [6] show large wings, which contain a significant amount of the energy. The additive-pulse-modelocking approach using the rejection port for output coupling [5] shows better pulse quality but depends on a rather sophisticated and expensive master-oscillator/power amplifier pump source. In this Letter we report the first demonstration of a passively CW modelocked diode-pumped bulk Er3+: Yb3+: glass laser yielding good stability and pulse quality.