Integrated array of 2-µm antimonide-based single-photon counting devices.

A 32x32 Sb-based Geiger-mode (GM) avalanche photodiode array, operating at 2 µm with three-dimensional imaging capability, is presented. The array is interfaced with a ROIC (readout integrated circuit) in which each pixel can detect a photon and record the arrival time. The hybridized unit for the 1000-element focal plane array, when operated at 77K with 1 V overbias range, shows an average dark count rate of 1.5 kHz. Three-dimensional range images of objects were acquired.

Miniature eye-safe laser system for high-resolution three-dimensional lidar.

A microchip-laser-pumped optical parametric amplifier produces 35-microJ, 1.537-microm pulses of 190-ps duration at 8 kHz, in a near-diffraction-limited output beam with a Fourier-transform-limited spectrum. The flight-ready laser head is pumped by 20 W of optical power from two fiber-coupled laser-diode arrays, occupies a volume of 0.14 liters, and has a mass of 0.34 kg.

Energy-scavenging amplifiers for miniature solid-state lasers.

Longitudinally pumped miniature lasers are inefficient, partly because of their inefficient absorption of the pump light. Scavenging the unabsorbed pump light to pump an in-line amplifier can greatly enhance the efficiency of the system, with minimal added cost, size, or complexity.

Periodically poled BaMgF(4) for ultraviolet frequency generation.

Ferroelectric domain inversion has been demonstrated in BaMgF(4) . Transparency has been measured to <140nm, and no change in transmission was measured under 157-nm irradiation for >1.1x10(9) shots at 2mJ/cm(2) per pulse. First-order quasi-phase-matched generation of 157 nm is predicted by use of grating periods as long as 1.5mum. This material should permit shorter-wavelength chi((2)) frequency-mixing processes than with any other crystalline material.

Diode-pumped 214.8-nm Nd:YAG /Cr4+:YAG microchip laser system for the detection of NO.

A passively Q-switched 214.8-nm Nd:YAG/Cr(4+):YAG microchip laser system for the detection of NO was designed, constructed, and tested. The system uses the fifth harmonic of the 1.074-microm transition in Nd:YAG to detect NO by laser-induced fluorescence. A significant challenge was the development of an environmentally stable coating to provide the necessary discrimination between the 1.074-microm laser line and the stronger transition at 1.064 microm. The exact position of the fifth-harmonic frequency was determined by use of NO fluorescence excitation spectra to be 46556 +/- 1.5 cm(-1). With a pulse energy of approximately 50 nJ of fifth-harmonic light, we observed a detection sensitivity for NO of approximately 15 parts per billion by volume in a simple, compact optical system.

Periodically poled lithium niobate optical parametric amplifiers pumped by high-power passively Q-switched microchip lasers.

High-power passively Q-switched microchip lasers produce 157-muJ pulses of 1-ns duration in a single-frequency, diffraction-limited output beam. The unfocused 1.064-mum output of these devices has been used to drive periodically poled lithium niobate optical parametric amplifiers at wavelengths between 1.4 and 4.3 mum . With a peak conversion efficiency of nearly 100%, these devices generate 100-kW, subnanosecond pulses in the mid IR, with a beam quality that is better than two times diffraction limited.

Single-mode high-peak-power passively Q-switched diode-pumped Nd:YAG laser.

We have demonstrated an efficient, compact, passively Q-switched single-mode diode-pumped Nd:YAG laser that uses Cr(4+):YAG as a saturable absorber. Linear- and ring-cavity configurations were demonstrated. Pulse energies and widths were, respectively, 1.5mJ and 3.9ns for the linear cavity and 2.1mJ and 12ns for the ring cavity.

Ultraviolet generation with passively Q-switchedmicrochip lasers.

First, second, third, fourth, and f ifth harmonics of the output of a f iber-pumped passively Q-switched Nd:YAG microchip laser have been obtained at pulse energies of 8.0, 3.5, 0.3, 0.7, and 0.01 microJ, respectively, in an optical head occupying a volume of less than 3 cm(3). This compact, economical all-solid-state source provides coherent subnanosecond multikilowatt infrared, visible, and ultraviolet pulses at repetition rates in excess of 10 kHz.

Coupled-cavity electro-optically Q-switched Nd:YVO(4) microchip lasers.

Nd:YVO(4) microchip lasers have been electro-optically Q switched to produce 12-microJ pulses of 115-ps duration at repetition rates of up to 1 kHz. At a repetition rate of 2.25 MHz, 0.16-microJ pulses with an 8.8-ns duration were obtained.

Tm:YVO(4) microchip laser.

When pumped with a 1-W laser diode, a Tm:YVO(4) microchip laser produced 150 mW of 1.92-µm output in a near-diffraction-limited beam at room temperature. Using a Ti:Al(2)O(3) laser to pump the same device, we showed that reducing the temperature of the Tm:YVO(4) from 20 to -30 °C resulted in no measurable change in threshold and increased the slope efficiency by only 20%.

Diode-pumped passively Q-switched picosecond microchip lasers.

Passively Q-switched 1.064-microm microchip lasers have been constructed from thin pieces of Nd(3+):YAG bonded to thin pieces of Cr(4+):YAG. When pumped with the unfocused 1.2-W output of a fiber-coupled diode, these devices produced 11-microJ pulses of 337-ps duration at a pulse repetition rate of 6 kHz in a single-frequency TEM(00) mode. The peak power of the lasers was in excess of 180 MW/cm(2).

Phase locking of 1.32-microm microchip lasers through the use of pump-diode modulation.

Two diode-pumped 1.32-microm Nd:YAG microchip lasers have been phase locked through the use of current modulation of the pump diode to control the frequency of the slave device. The frequency response of the microchip laser to pump-diode modulation is discussed, and the feedback circuit is described.

Diode-pumped microchip lasers electro-optically Q switched at high pulse repetition rates.

We have obtained asymptotically equal to50 mW of time-averaged 1.064-microm output power from a diode-pumped, electro-optically Q-switched Nd:YAG microchip laser at pulse repetition rates between 5 and 500 kHz. The FWHM of the output pulses is proportional to the repetition rate, varying from <300 ps at low repetition rates to 13.3 ns at 500 kHz. The multikilowatt peak power obtained at low repetition rates allows for efficient nonlinear frequency conversion and is sufficient to ablate thin layers of metal.

Limits imposed by spatial hole burning on the single-mode operation of standing-wave laser cavities.

A simple formula is derived that gives the ratio of the maximum single-longitudinal-mode inversion density to the threshold inversion density for a standing-wave laser in terms of the cavity geometry and well-known material parameters. This formula can be used as a guideline in the design of single-frequency lasers.

Single-frequency microchip Nd lasers.

Optically pumped, single-frequency, Nd-doped, solid-state lasers have been constructed using flat-flat cavities, which were diced from large dielectrically coated wafers of various crystals. For example, a Nd:YAG laser with a cavity length of 730 microm has operated at room temperature in a single longitudinal mode from a threshold of less than 1 mW to greater than 40 times the threshold. Theslope efficiency was greater than 30%. Heterodyne measurements showed an instrument-limited linewidth of 5 kHz. The microchip lasers demonstrate ways to reduce greatly the cost and complexity offabricating small lasers and electro-optic devices.

Frequency-modulated Nd:YAG microchip lasers.

Tunable, single-frequency, Nd:YAG microchip lasers have been piezoelectrically frequency modulated over several hundred megahertz at rates from dc to 25 MHz.

Gain-switched pulsed operation of microchip lasers.

Microchip lasers have produced single-frequency, gain-switched pulses with a FWHM as short as 760 psec for Nd:YAG (Nd(x)Y(3-x)Al(5)O(12)) and 80 psec for LiNdP(4)O(12) (LNP).