We demonstrate 30 W of average UV power, at 353 nm, by harmonically converting the output of a seeded
cascade of fiber amplifiers operating at 1060 nm. The UV output represents 46% harmonic conversion
efficiency from the fundamental beam. The all-fiber-amplifier, MOPA architecture supports variable pulse
repetition frequencies and pulse widths. We demonstrate pulse repetition frequencies up to 2 MHz and
pulse widths as short as 2 ns. Two bulk LBO crystals, oriented for second and third harmonic conversion,
are used to obtain stable UV output power. A turnkey system using this architecture is commercially
available. The system is entirely air-cooled and operates from a standard wall plug electric service,
facilitating integration into various material processing applications.
Many micromachining operations, particularly in the electronics sector, utilize pulsed solid-state UV lasers. These processes demand high levels of stability, as the yield and quality relate directly to the repeatability of each laser pulse. Critical stability issues arise with single-pulse processes (e.g. repair), situations requiring bursts of pulses (e.g. drilling), and continuous pulsing applications (e.g. cutting). To realize optimal stability specific design choices must be made, certain transient problems must be solved, and pulse energy measurements must be standardized. Solid-state UV lasers originate as infrared lasers, and nonlinear optics converts the infrared to the UV. This conversion introduces instability. Performing the conversion within the infrared laser cavity suppresses the instability, relative to performing the conversion outside of the laser cavity. We explain this phenomenon. Ideally, a versatile and stable solid-state laser can generate pulses in many formats. Thermal effects tend to prevent this versatile ideal, resulting in transient problems (unstable pulse trains), or less than optimal performance when the laser is pulsing continuously. Many methods of measuring pulse energy exist. Each method can produce surprisingly different results. We compare various techniques, discuss their limitations, and suggest an easily implemented pulse energy stability measurement.
The trend in micro-machining lasers is toward greater average power and higher repetition rate, in order to increase throughput, with pulse energy and peak power held roughly constant, as determined by the small scale of the feature. At repetition rates beyond 500 kHz, conventional high-power Q-switched Nd lasers will reach fundamental limits. We demonstrated a fiber-based oscillator-amplifier architecture which produces pulse repetition rates in the 0.5 - 5 MHz range and pulse durations in the 0.5 - 1.5 nsec range. The oscillator is a compact (35 cm<sup>3</sup> package) passively Q-switched Nd:YVO<sub>4</sub> laser oscillating at a single frequency. By amplifying this laser in fiber, we demonstrated 10-W average power at the two wavelengths of 914 nm and 1064 nm. At 1064-nm, Yb-doped large mode area fiber will allow scaling of average power to over 100 Watts, with peak power of tens of kW, in a diffraction-limited beam. Excellent conversion will be possible to visible and UV using the robust nonlinear material LBO. By opening up a new range of repetition rates and pulse lengths, at IR, visible and UV wavelengths, in a high power design that has the packaging and efficiency advantages of fiber, new micro-machining applications may be enabled.
S-band amplification with >30 dB peak gain at 1500 nm, >20 dB gain for wavelengths between 1475 nm and 1520 nm, and 5 dB noise figure is demonstrated in Erbium-doped Alumino-germanosilicate fiber. Using standard MCVD processing and solution doping, we combined a depressed-cladding fiber design with erbium doping to create a new type of gain fiber. A fundamental mode cutoff near 1530 nm provides distributed suppression of C-band amplified spontaneous emission, thereby enabling the high population inversion required for S-band gain. This type of S-band amplifier is compatible with standard fusion splicing techniques and is pumped by standard 980 nm pump lasers. In this talk, we will describe gain and noise characteristics for several amplifier architectures, gain saturation characteristics, and gain flattening.
We report the first demonstration of mid-IR coherent laser radar operation near 3.6 micrometers . In many low altitude environments, the wavelength region from 3.5 - 4 micrometers has advantages for laser beam propagation because the detrimental effects of scattering and turbulence are less severe than at shorter wavelengths. In addition, under conditions of high humidity, water vapor absorption in the mid-IR is also significantly lower compared to the long-IR region at 9-11 micrometers . The source in this work is a 100 mW, frequency stable cw-optical parametric oscillator (OPO) based on periodically poled lithium niobate. The frequency stability of the source is discussed and laboratory heterodyne experiments measuring small Doppler shifts from vibrating targets are described.
A 1560 nm external cavity diode laser was efficiently doubled in a periodically poled LiNbO<SUB>3</SUB> waveguide and locked to <SUP>87</SUP>Rb sub-Doppler lines near 780 nm. Its frequency stability was characterized by measuring the beat frequency relative to a 780 nm external cavity diode laser which was locked to sub-Doppler lines of another Rb cell. The root Allan variance reached a minimum value of 6.9 X 10<SUP>-12</SUP> in 1 s, which corresponded to frequency variations of 1.3 kHz for the 1560 nm laser.