A dental laser arrangement switchable between different modes of operation, the arrangement including a laser device operable as a laser oscillator and as a laser amplifier. The laser device includes a laser resonator having a pump unit and an active modelocker as well as an optic loss element that introduces selective losses in the resonator. The laser arrangement further includes a laser beam-out-coupling unit. The modelocker is connected to a control circuit for switching between a CW-mode of operation for coagulating soft tissue, in which the modelocker is switched off, and two short-pulse modes of operation in which high frequency signals of equal frequencies, but different powers are applied by the control circuit to the modelocker so as to generate laser pulses of a pre-determined duration. One of the two short-pulse modes of operation is provided for ablation of hard tooth tissue, and the other short-pulse mode of operation, in which the laser radiation has a lower peak power in comparison with the first-mentioned short-pulse mode of operation, is for surface sealing of hard tooth tissue. An output of the control circuit furthermore is applied to the activatable optic loss element for controlling the losses in the resonator in the short-pulse modes of operation.

A method of operating a continuously pumped, Q-switched laser to provide trains of pulses for laser operations is disclosed. The laser includes a solid-state gain-medium that exhibits a thermal-lensing effect on being optically pumped. Pulse delivery is controlled by a Q-switch that is in a normally-open state when the laser is not delivering pulses. This allows the laser to deliver CW laser radiation when pulses are not being delivered. A train of pulses is delivered by repeatedly interrupting the CW operation by closing then reopening the Q-switch. When the Q-switch reopens after the interruption, the laser delivers a pulse of laser radiation, then resumes delivery of CW operation until the next interruption. The inventive Q-switching method provides, by means of this one particular repeated Q-switch operation, that the thermal-lensing effect in the gain-medium before, during, and between delivery of pulse trains remains constant, and that all pulses in a pulse train have the same peak power.

A method of operating a continuously pumped, Q-switched laser to provide trains of pulses for laser operations is disclosed. The laser includes a solid-state gain-medium that exhibits a thermal-lensing effect on being optically pumped. Pulse delivery is controlled by a Q-switch that is in a normally-open state when the laser is not delivering pulses. This allows the laser to deliver CW laser radiation when pulses are not being delivered. A train of pulses is delivered by repeatedly interrupting the CW operation by closing then reopening the Q-switch. When the Q-switch reopens after the interruption, the laser delivers a pulse of laser radiation, then resumes delivery of CW operation until the next interruption. The interruption periods may be varied to provide pulses of different peak power in a pulse train.

Preferred embodiments of a system and methods to deliver different magnitudes of laser power density to a work piece while maintaining a constant focusing spot size are described. In particular, the system includes a laser, an optical focusing assembly and an overlay. The overlay receives a laser beam having a perimeter at a first magnitude of power and transmits the laser beam to the optical focusing assembly at about the same perimeter and at a magnitude lower than the first magnitude. In a preferred embodiment, the overlay can include an optically neutral blocking lens or a neutral density filter. A method of laser machining an orifice at a suitable average power density sufficient to machine the orifice with reduced heat affected zone, spatters, soots or recasts is described. A method of providing a focusing spot size of a generally constant effective area by a laser machining system is also described.