Abstract

In recent years, chromium doped ZnSe has become of increasing interest due to very efficient laser operation in the spectral range around 2.4μm [1]. Slope efficiencies of up to 73% and a maximum output power of 1.8W have been demonstrated. Furthermore, mode-locking, gain-switching, pulsed and continuous wave diode pumping have been realised so far. The broad spectral tuning range between 2134nm and 2860nm in continuous wave operation offer a wide field of application, like remote sensing, trace gas analysis and the use in medical devices. Especially for the latter, the long-wavelength range of tunability is of particular interest due to the maximum of water absorption near 2.9μm. A much further expansion of the tuning range towards shorter wavelengths is not expected, because of ground state absorption in this region. On the other hand, the possibility of laser operation beyond 3μm was proven in an earlier paper by means of excited state absorption and gain measurements [2]. This has now been confirmed in experiment. The pump source was a Q-switched Tm:YAG-laser operating at a wavelength of 2.01μm with a pulsewidth between 500 and 1000ns. The tuning element inside the Cr²⁺:ZnSe laser was a ZnSe prism. Laser oscillation up to a wavelength of 3040nm was obtained in this pulsed laser pumped operation. The shape of the laser pulses is shown in Fig. 1. After some short pulses, the Cr²⁺:ZnSe laser follows the pump pulse of the Tm:YAG laser. The maximum output energy was 0.7mJ at 2400nm. Detailed results of the tuning experiments will be presented - at the conference. Thus, the Cr²⁺:ZnSe laser has a total spectral tuning range from 2134nm up to 3040nm, i.e. a spectral bandwidth of 906nm. It therefore compares to the broad tunability of the titanium sapphire laser.

© 2001 EPS