We describe a passively mode-locked, diode-pumped Nd:YAG laser that is used for frequency-conversion applications. The laser is based on a Direct-coupled Pump gain element and saturable Bragg reflector. The laser produces a 20-ps pulse with a 100-MHz repetition rate in a compact commercial package. It has typically <0.2% amplitude noise and diffraction-limited output beam. The average power is typically 7-8 W, and peak power is 4 kW which makes it well-suited for efficient frequency conversion. Using 2 stages of LBO for cascaded second-harmonic and sum-frequency generation, we have obtained >1 W at 355 nm. In addition, we have generated super-continuum output in the visible and infrared from micro-structured nonlinear fiber with pumping both at 1064 nm and 532 nm. Current applications for this laser, primarily in the ultraviolet, include flow cytometry, stereolithography, and semiconductor inspection.
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.
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 a new type of optical parametric oscillator (OPO) cavity, i.e. a compound cavity OPO, and present its time dynamics based on a mathematical model. Both the numerical simulation and experimental results show that this type of cavity is superior in that its threshold is lower than that of a simple narrow-band cavity with dispersive elements, and its external efficiency is increased while its narrow linewidth remains nearly the same across the tunable range of the nonlinear crystals used.