We report room-temperature operation of what we believe is the first continuous-wave laser that relies exclusively on cooperative upconversion by coupled ion pairs to achieve population inversion.

Recent demonstrations 1-5 of room-temperature upconversion lasers have stirred interest in their potential as practical sources of short wavelength radiation for display and data storage applications, as well as for communications and ultrashort pulse generation at visible and ultraviolet wavelengths.6 To date however, little consideration has been given to the relative merits of various fundam...

The first laser to operate with an output wavelength shorter than that of the excitation was a pulsed erbium laser reported by Johnson and Guggenheim.l Since this early work, a variety of continuous-wave lasers have been reported in which upconversion occurs by different mechanisms, and inversions of upconverted energy levels have been sustained by avalanche processes, 2.3 direct pairpumping,4 ...

In continuous wave ultrasonic Doppler tomography (DT), the ultrasonic beam moves relative to the scanned object to acquire Doppler-shifted frequency spectra which correspond to cross-range projections of the scattering and reflecting structures within the object. The relative motion can be circular or linear. These data are then backprojected to reconstruct the two-dimensional image of the obje...