VECSEL Semiconductor Lasers: A Path to High‐Power, Quality Beam and UV to IR Wavelength by Design

Since its invention and demonstration in 1960, several types of laser have been developed, such as solid-state, semiconductor, gas, excimer, and dye lasers [1]. Today, lasers are used in a wide range of important applications, particularly in optical fiber communication, optical digital recording (CD, DVD, and Blu-ray), laser materials processing, biology and medicine, spectroscopy, imaging, entertainment, and many others. A number of properties enable the application of lasers in these diverse areas, each application requiring a particular combination of these properties. Some of the most important laser properties are laser emission wavelength; output optical power; method of laser excitation, whether by optical pumping or electrical current injection; laser power consumption and efficiency; high-speed modulation or short pulse generation ability; wavelength tunability; output beam quality; device size; and so on. Thus, optical fiber communication [2], a major application that enables modern Internet, commonly requires lasers with emission wavelengths in the 1.55mm lowloss band of glass fibers and with single-transverse mode output beams for coupling into single-mode optical fibers. Typically, a given laser type excels in some of these properties, while exhibiting shortcomings in others. For example, by using different material compositions and structures, the most widely used semiconductor diode laser [3–12] can cover a wide range of wavelengths from the ultraviolet (UV) to the mid-IR, can be advantageously driven by diode current injection, and is very compact and efficient. However, the good beam quality, that is, single-transverse mode nearcircular beam operation, can be typically achieved in semiconductor lasers only for output powers below 1W. Much higher power levels are achievable from semiconductor lasers only with large aspect ratio highly multimoded poor quality optical beams. On the other hand, the solid-state lasers [13, 14], including fiber lasers [15], can emit hundreds of watts of output power with excellent beam quality, however, their emission wavelengths are restricted to discrete values of electronic transitions in ions, such as the classic 1064 nm wavelength of the Nd:YAG laser, making them