Kenneth M. Dinndorf

Characterization of passively Q-switched microchip lasers for laser radar

Here we report the characterization of the temporal jitter of a passively Q-switched Nd:YAG microchip laser. We experiment with different control schemes to reduce the observed jitter. Measurements were made for microchip laser temperatures from 10 degree(s) to 50 degree(s)C. The microchip laser was operated at various pulse rates from 500 Hz to 26 kHz.

Compact multichannel receiver using InGaAs APDs for single-pulse eye-safe laser radar imagery

Active imaging laser radars form 3D images which can be processed to provide target identification and precision aimpoint definition in real time. Earlier raster-scanned and pushbroom-scanned 3D imaging laser radar receivers required multiple laser pulses to assemble a complete 3D image frame. Platform/target motion and atmospheric effects caused tearing and jitter in the assembled 3D images, which complicated the subsequent image processing and necessitated the use of stabilized scanning systems. This paper describes the current status of the parallel/multichannel imaging laser radar receiver (PMR) which is being developed under an SBIR Phaser II program by the USAF Wright Laboratories Armament Directorate. The PMR uses an array of multichannel laser radar receivers to form single-pulse, 3D laser radar images, thus eliminating the complex and costly scanning system, and enabling much higher frame rates than were ever before possible. The heart of the PMR is the multichannel optical receiver photonic hybrid (MORPH), a high performance 16-channel laser radar receiver module which uses an array of InGaAs avalanche photodiodes for eyesafe operation. The MORPH provides high downrange resolution, multihit range data for each detector on a compact circuit card. Optical flux is transferred from the receiver focal plane to each MORPH via a fiber optic ribbon cable. An array of MORPHs are plugged into a compact passive backplane, along with a single digital control card (DCC). The DCC, which is the same form factor as the MORPH, synchronizes the MORPHs and transfers the digital range information to the host processor over a standard parallel data interface cable. The system described here illustrates one approach to integrating and packaging high-density photonic arrays and their associated signal processing electronics to yield a compact, low power, scannerless, high performance imaging laser radar receiver, using existing technology.

Distribution of Stored Energy in the Excited Manifolds of Tm and Ho in 2 Micron Laser Materials

We determine the quasi-equilibrium distribution of the excitations between the excited states of Tm and Ho. We find that the distribution is excitation density dependent and is described by a canonical summation over the energy levels of the excited and ground state manifolds. We discuss the implications of this distribution for 2 micron lasers.

High-pulse-energy 3.9-μm lasers in Ho:BYF

Experimental results describing pulsed lasers operating near 3.9 μm on the Ho3+ (5I5-5I6) transition in highly-doped (> 10 at. %) barium yttrium fluoride (BaY2F8 or BYF) will be presented. The 5I5 manifolds in Ho:BYF were pumped using a flashlamp excited, free-running Cr:LiSAF laser tuned to the Ho3+ absorption peak near 889nm. Ho3+ concentrations of 10%, 20%, 30% and 40% in BYF were lased in a simple end-pumped resonator. Some similar data was also obtained in 10% and 20% Ho:YLF. The highest 3.9 μm pulse energy obtained in the comparative study was 55 mJ (at ~10% optical-to-optical efficiency) using the 30% Ho:BYF crystal. A dual end-pumped laser in 30% Ho:BYF was also demonstrated, providing a pulse energy of 90 mJ in a near diffraction limited beam (M2 ~ 1.2). Emission decay data was taken to shed light on the observed dependence of laser efficiency on holmium concentration and excitation density. The lifetimes of both lasing levels (5I5 and 5I6) deviate rather significantly from their low-concentration values. Plausible energy transfer processes that may be responsible for the observed trends in the laser and emission data will also be discussed.

Two Micron Diode-Pumped Laser Operation of Tm,Ho:BaY2F8>

Diode-pumped Tm, Ho:BaY2F8 was operated as a room-temperature two micron laser. Laser results and various spectroscopic parameters are reported.

Long-range imaging ladar flight test

Wright Laboratory and Loral Vought Systems (LVS) have been involved for the last nine years in the research and development of high power diode pumped solid state lasers for medium to long range laser radar (LADAR) seekers for tactical air-to-ground munitions. LVS provided the lead in three key LADAR programs at Wright Lab; the Submunition Guidance Program (Subguide), the Low Cost Anti-Armor Submunition Program (LOCAAS) and the Diode Laser and Detector Array Development Program (3-D). This paper discusses recent advances through the 3-D program that provide the opportunity to obtain three dimensional laser radar imagery in captive flight at a range of 5 km.

Near-diffraction limited 65 W Nd:YLF laser

One of the primary challenges to obtaining diffraction-limited performance in high-power solid state lasers is compensating for the thermally-induced optical effects[i].