For high-resolution spectroscopy, a stable, narrow linewidth and high power output laser is desirable in order to pump different types of resonant optical parametric oscillators, which is the goal of the present work. Typical single frequency pump lasers are in the range of 10 watt output power whereas, depending on application and OPO type, higher power (>20 W) is desirable. Here we demonstrate a high-power single frequency laser based on off the shelf standard Nd:YAG pump modules. Two closely spaced, diode-side-pumped Nd:YAG rods were used in a mode-filling configuration to form a CW polarized ring resonator with TEM<sub>00</sub> beam quality and output power of 105 W. The output power achieved is, to our knowledge, the highest reported for continuous polarized, fundamental-mode ring lasers using standard side-pumped Nd:YAG modules. The resonator allowed for power tuning over a large dynamic range and achieved excellent beam quality, using a half wave plate between both rods for birefringence compensation. Single frequency operation was achieved using a TGG crystal and an etalon, with a preliminary output power of 40 W.
Nd:YLiF4 is the gain material of choice whenever outstanding beam quality or a birefringent gain material is necessary such as in certain applications for terahertz radiation or dual-frequency mode-locking. However, for high power CW applications the material is hampered by a low thermal fracture threshold. This problem can be mitigated by special 2D pump set-ups or by keeping the quantum defect to a minimum. Direct pumping into the upper laser level of Nd:YLiF4 is usually performed at 880 nm. For quasi-three level laser emission at 908 nm, direct pumping at this wavelength provides a high quantum defect of 0.97, which allows for very high CW pump powers. Although the direct pumping transition to the upper laser state at 872 nm has a slightly smaller quantum defect of 0.96, its pump absorption cross section along the c-axis is 50% higher than at 880 nm, leading to a higher absorption efficiency. In this work we explore, for the first time to our knowledge, 908 nm lasing under 872 nm diode pumping and compare the results with 880 nm pumping for quasicw and cw operation. By inserting a KGW crystal in the cavity, Raman lines at 990 nm and 972 nm were obtained for the first time from a directly pumped 908 nm Nd:YLF fundamental laser for both quasi-cw and cw conditions.
A cubic-phase distribution is applied in the design, fabrication and characterization of inexpensive Fresnel lens arrays for
passive infrared motion sensors. The resulting lens array produces a point spread function (PSF) capable of distinguish
the presence of humans from pets by the employment of the so-called wavefront coding method. The cubic phase
distribution used in the design can also reduce the optical aberrations present in the system. This aberration control
allows a high tolerance in the fabrication of the lenses and in the alignment errors of the sensor. In order to proof the
principle, a lens was manufactured on amorphous hydrogenated carbon thin film, by well-known micro fabrication
process steps. The optical results demonstrates
that the optical power falling onto the detector surface is attenuated for
targets that present a mass that is horizontally distributed in space (e.g. pets) while the optical power is enhanced for
targets that present a mass vertically distributed in space (e.g. humans). Then a mould on steel was fabricated by laser
engraving, allowing large-scale production of the lens array in polymeric material. A polymeric lens was injected and its
optical transmittance was characterized by Fourier Transform Infrared Spectrometry technique, which has shown an
adequate optical transmittance in the 8-14 μm wavelength range. Finally the performance of the sensor was measured in
a climate-controlled test laboratory constructed for this purpose. The results show that the sensor operates normally with
a human target, with a 12 meter detection zone and within an angle of 100 degrees. On the other hand, when a small pet
runs through a total of 22 different trajectories no sensor trips are observed. The novelty of this work is the fact that the
so-called pet immunity function was implemented in a purely optical filtering. As a result, this approach allows the
reduction of some hardware parts as well as decreasing the software complexity, once the information about the intruder
is optically processed before it is transduced by the pyroelectric sensor.