Fiber laser pumped Er:YOS laser action near 1600 nm was achieved at room temperature. Etalons and a diffraction grating were used to generate and control broad-band laser action near the 1600 nm emission center. Efficient operation was achieved in a non-optimized laser test bed.
We demonstrate passively Q switched 2% doped Er:YAG laser operation in the eyesafe region with sub 5 nsec pulse widths using Cr<sup>2+</sup>:ZnSe as a saturable absorber. A rod geometry operating in the burst mode and a micro slab geometry operating continuously are described. The micro slab geometry generates 6nsec passively Q switched pulses with over 1.5 Watt of output power and with multi kilohertz pulse repetition rates. The lasers are resonantly pumped with a 1534nm fiber laser.
We demonstrate Er:YAG laser operation at 1617nm with 6W output power and good beam quality (M-squared = 1.5) using a Volume Bragg Grating (VBG) as a wavelength selective output coupler. The low quantum defect operation of 5% is achieved by resonant pumping with a 1534nm fiber pump laser. The thermal loads of the crystal under 1617nm laser operation, under 1645nm laser operation, and under a no lasing condition are determined.
1534 nm Fiber laser pumped Er:YAG laser action at room temperature has been demonstrated with high efficiency. CW power as high as 12 Watts was achieved at 1645 nm from Er:YAG where a single TEC controller was used for thermal management. Active EO Q-switched operation with kHz repetition rate and 27 ns pulse widths was achieved with the same laser resonator.
Fiber laser pumped Er:YAG laser action at 1617 nm was achieved at room temperature. An etalon was utilized for tuning the laser to the 1617 nm line. Room temperature operation was characterized and compared with 1645 nm operation. Output power close to 3 Watts CW was demonstrated at the 1617 nm laser line.
There is a need for real-time unobtrusive monitoring of the vital body chemistry and general health status of military personnel during training and in hostile battlefield environments. Monitoring the health of a soldier who is an integral part of a military mission is important, because a compromise in his/her ability to act at a certain moment could jeopardize the operation. The most accessible measure of a person's health at any given instant is his/her anaerobic metabolism rate (O<SUB>2</SUB> debt), which is indicative of the changes in skeletal muscle and cerebral oxygenation. Anaerobic metabolism data can be used by paramedics to save lives. Lactate levels are important measure of oxygen debt. Lactate is a weak acid that is produced by cells when they break down glucose to produce energy by anaerobic metabolism (a chemical process that does not require oxygen). In this project we developed, constructed, and tested a compact personal optical sensor for monitoring lactate via sweat metabolite analysis. The sensor quantifies the change of the optical properties caused by lactate chemistry. Our miniaturized noninvasive lactate sensor measures minute changes of the lactate between 0-130 mM in near real time.
In this paper, we describe the temporal laser pulse dynamics of the 1.645 micrometers Er:YAG laser pumped by a 1.532 micrometers Er:glass laser. It can be shown that controllable double pulsing of the 1.645 micrometers laser action can be obtained by gain-switched type operation and a variable cavity loss. The rate equation dynamics model can predict this behavior, and thereby provide a design platform for generating controllable double pulsing outputs at high repetition rates. Applications to lidar techniques are discussed. Some innovative applications include polarization discrimination techniques in target detection technology and mitigating atmospheric turbulence effects in measurements.
The generation of 84 GHz radiation was demonstrated using a mode-locked semiconductor laser (MLSL) pumped heterojunction bipolar transistor (HBT). The passively mode-locked MLSL was biased appropriately utilizing two diode laser drivers (current sources). Mode-locked behavior was achieved in a colliding pulse mode, resulting in a pulse repetition rate frequency of approximately equals 84 GHz. The mode-locked behavior was confirmed by utilizing both an interferometer-based correlation measurement and an optical spectrum analyzer. The MLSLO was then used to pump an HBT that was specially designed for optical pumping (a 10 mm X 10 mm window was fabricated in the HBT), allowing efficient optical excitation of the device. HBT-radiated MMW signals as high as 20 dB (above the noise floor) were achieved at approximately equals 84 GHz.
The WKB (Wentzel-Kramers-Brillouin) method, well-known in quantum mechanics, is applied in the second-order approximation into non-uniform Bragg structure, such as rugged dielectric thin films, sinusoidal gratings, and holograms. In this paper, the analytic WKB problem solution will be presented including numerical results.
The potential utilization of volume diffractive elements (VDOEs) in a variety of sophisticated imaging applications has been established. VDOEs are capable of designed-in arbitrary phase distributions (indigenous to multi-layer diffractive structures), while maintaining high diffraction efficiencies (exhibited in volume holographic optical elements (HOEs)). Furthermore, multi-layer VDOE structure facilitates further improvement over HOEs. High diffraction efficiencies with simultaneous side lobe suppression can be achieved in VDOEs, while narrow bandwidths and desirable free spectral ranges are maintained. In this paper, we show that with proper utilization of VDOE and spacer thickness, we can achieve efficient side lobe suppression in the behavior of the diffraction efficiency, as a function of both incident wavelength and angle.
We investigated a new type of optical element: volume diffractive optical element (VDOE). The uniqueness of the VDOE approach lies in the fact that it can exhibit a high diffraction efficiency (indigenous to a volume holographic optical element (HOE), while sporting a multi-diffractive layer structure amenable to standard lithographic manufacturing techniques. Computer design flexibility and the capability of effecting an arbitrary phase function in a VDOE provide a number of potential applications for these optical elements. Specifically, space telescope and image multiplication are discussed. Our theoretical modeling of the VDOE utilizes the rigorous coupled wave theory, which allows us to introduce an arbitrary VDOE/spacer layer thicknesses, grating slant angles, wavelengths, and incident angles. In addition, our model can simulate a multi-layer phase shifted VDOE structure (important in simulating HOE structures by a multi-layer VDOE design).
The operation of several singlemode erbium doped polymer waveguide amplifiers was demonstrated. Optical gain of 5 dB was achieved at two different signal laser wavelengths, using a 1.48 micrometers pump. The two polymer host in which gain was demonstrated were gelatin and polystyrene - both prepared in a waveguide structured with high doping levels.
It is known that if the drug uptake by a tumor is below the required concentration the efficacy of PDT can be significantly reduced. There is, therefore, a need for a photodynamic drug detection (PD<SUP>3</SUP>) system to be used with PDT to monitor the drug concentration in tissue in real time and noninvasively. The system developed integrates laser, a fiber optic probe, and an optical detector to detect photodynamic drugs (Photofrin II, Protoporphyrin IX, and BPD). A series of drug concentrations was measured based on the detection of diffusely fluorescence photons. The fluorescence peak at 680 nm is suggested for intensity measurement. The effect of fluorescence reabsorption was observed when using high concentration Photofrin solutions. When PD<SUP>3</SUP> is used in conjunction with monitoring through an endoscope, the system offers spectral information (displayed on a computer monitor) in addition to the conventional image (displayed on an endoscope monitor).
The 1.645 (mu) laser action in Er<SUP>3+</SUP>:Y<SUB>3</SUB>Al<SUB>5</SUB>O<SUB>12</SUB> (Er:YAG) at 300 K was studied using the 1.532 micrometers Er:glass laser for excitation. Laser action was with Er concentrations ranging from 0.5% to 4%. Slope efficiencies as high as 40% were obtained with 0.5% Er:YAG. Laser threshold results indicated that for this Er concentration range upconversion losses were small (negligible for 0.5% Er).
The <SUP>4</SUP>I<SUB>13/2</SUB> - <SUP>4</SUP>I<SUB>15/2</SUB> laser action in Er<SUP>3+</SUP>:Y<SUB>3</SUB>Sc<SUB>2</SUB>Ga<SUB>3</SUB>O<SUB>12</SUB> (Er:YSGG) at room temperature is described. We obtained 1.643 micrometers laser action from a 1 cm long 0.7% Er (3% Yb, 1% Cr):YSGG crystal with a 20 mJ pump threshold and an 8% slope efficiency utilizing an Er:glass 1.532 (mu) pump laser.