Princeton Optronics (United States)

Lean-burn natural gas engines remain attractive as they offer low emissions with simultaneous high engine efficiency. The low carbon to hydrogen ratio in natural gas minimizes the carbon dioxide emission, while the low-temperature operation reduces NOx formation. However, to preserve engine specific power, turbo-charged operation is required, which results in an unfavorable environment for the spark ignition system. In this study, the performance of three ignition systems - Spark Ignition (SI), Laser Ignition (LI), and Prechamber Laser Ignition (PCLI) - were assessed through tests in a single-cylinder natural gas engine. Both λ and ignition timing sweeps were performed while maintaining a constant speed of 1800 rpm and a load of 10 bar BMEP. Emissions and combustion data analysis, while complying with allowable emission regulation and ignition stability requirements, showed the best performance to be achieved with the PCLI system. This is attributed to improved ignition with the use of a laser, volumetric ignition facilitated by spatially distributed flame jets, and increased in-cylinder turbulence. This results in reduced ignition delay and shortened combustion duration.

High power 808 nm VCSEL arrays were developed to pump compact pulsed Nd:YAG lasers. A QCW side-pumped passively Q-switched Nd:YAG laser operating at 1064 nm produced linearly polarized 4 ns IR pulses with 4.7 mJ pulse energy. These pulses were externally frequency doubled and quadrupled resulting in 2.5 mJ pulse energy at 532 nm and 0.8 mJ at 266 nm respectively. A similar but actively Q-switched dual side-pumped Nd:YAG laser operating at the weaker quasi three-level 946 nm transition produced 12 mJ pulses that were efficiently frequency doubled resulting in 5.6 mJ blue pulses of 17 ns duration.

We are developing a low noise high power ultra-stable diode pumped Er-Yb co-doped phosphate glass laser. Erbium doped phosphate glass permits high co-doping with ytterbium ions that strongly absorb at 976 nm and efficiently transfer their energy to the active erbium material. This drastically decreases the absorption length at the 976 nm pump wavelength and thus the overall size of the laser. Aside from the advantage for packaging a short cavity length results in a large longitudinal mode-spacing (>40 GHz), which allows for single longitudinal mode operation in the 1530-1565 nm C-band for telecommunication by inserting a tunable low-finesse etalon in the laser cavity. In addition, due to the energy transfer between the co-dopant and the active material, the laser shows a strongly reduced sensitivity to fluctuations in pump power. The strong peak in the RIN spectrum at the relaxation oscillation frequency (0.1-1 MHz) due to cavity-loss perturbations can be drastically reduced with a non-linear absorbing material inside the laser cavity. Using this approach for an optimized laser cavity design we have achieved -160 dB/Hz RIN at 1 MHz for 35 mW output. Above 100 MHz the RIN becomes shot noise limited (-168 dB/Hz @ 20mA photocurrent). The laser has excellent long-term frequency stability when locked to our wavelength locker (<250 kHz). Furthermore, the laser has been shown to have a narrow intrinsic linewidth (~10 Hz) that we are working towards by means of intra-cavity phase modulation.

Princeton Optronics is a participant of the SHEDS program. In this program, we are developing high power, high efficiency VCSEL devices and arrays for pumping solid state lasers. VCSELs have a number of advantages over edge emitters which include: manufacturing simplicity, easy scalability in the form of 2D arrays for higher power, higher reliability because of lower power density in the aperture, and lower temperature sensitivity for wavelength shift (5X lower). Our approach to the design of high power VCSELs is a novel design and heat sinking of the active side of the device by mounting it face down on a diamond substrate. In the SHEDS program we have been able to improve the efficiency significantly, and to improve the array power to 80 W from a 5X5 mm array. We plan to develop 500 W output from a 10X10 mm array in the future. The temperature and wavelength uniformity achieved over the array in impressive. We have achieved a temperature uniformity of +/-5 deg C and a wavelength uniformity of +/-0.5 nm over the 80 W arrays. We have achieved an impressive yield of 80% for the 80 W arrays (with all devices working). With a partial n-mirror on the VCSEL and using a volume Bragg grating (VBG) in an external cavity configuration, we have achieved extremely narrow linewidth for the laser.Princeton Optronics is a participant of the SHEDS program. In this program, we are developing high power, high efficiency VCSEL devices and arrays for pumping solid state lasers. VCSELs have a number of advantages over edge emitters which include: manufacturing simplicity, easy scalability in the form of 2D arrays for higher power, higher reliability because of lower power density in the aperture, and lower temperature sensitivity for wavelength shift (5X lower). Our approach to the design of high power VCSELs is a novel design and heat sinking of the active side of the device by mounting it face down on a diamond substrate. In the SHEDS program we have been able to improve the efficiency significantly, and to improve the array power to 80 W from a 5X5 mm array. We plan to develop 500 W output from a 10X10 mm array in the future. The temperature and wavelength uniformity achieved over the array in impressive. We have achieved a temperature uniformity of +/-5 deg C and a wavelength uniformity of +/-0.5 nm ...

High spatial resolution imaging with terahertz pulses is implemented with a novel collection-mode near-field probe. The spatial resolution capabilities of the system are in the range of few micrometers. We demonstrate resolution of 7 /spl mu/m using 0.5-THz pulses and discuss performance of the collection-mode near-field probes and image properties.