John J. Zayhowski

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).

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.

Three-dimensional imaging laser radar with a photon-counting avalanche photodiode array and microchip laser

We have developed a threedimensional imaging laser radar featuring 3-cm range resolution and single-photon sensitivity. This prototype direct-detection laser radar employs compact, all-solid-state technology for the laser and detector array. The source is a Nd:YAG microchip laser that is diode pumped, passively Q-switched, and frequency doubled. The detector is a gated, passively quenched, two-dimensional array of silicon avalanche photodiodes operating in Geigermode. After describing the system in detail, we present a three-dimensional image, derive performance characteristics, and discuss our plans for future imaging three-dimensional laser radars.

Optimization of Q-switched lasers

The authors extend the standard rate equation analysis to obtain expressions for the maximum peak power, maximum pulse energy, and minimum pulsewidth of a single Q-switched output pulse; the maximum power efficiency of a repetitively Q-switched laser; and the corresponding cavity output couplings. Results are obtained analytically and numerically, and a comparison of the two sets of results is made. As a first step in this process the authors derive general expressions for the peak power, pulsewidth, pulse energy, and power efficiency. The authors next differentiate these expressions in order to find the maxima or minima that optimize the parameter of interest. Differentiation is done with respect to the cavity output coupling. >

Passively Q-switched Nd:YAG microchip lasers and applications☆

Passively Q-switched Nd:YAG microchip lasers are robust, compact, economical, all-solid-state sources of coherent, subnanosecond, multikilowatt pulses at high repetition rates. When pumped with the cw output of commercially available infrared diode lasers, these diminutive, quasi-monolithic devices produce 1.064-μm pulses with a pulse width as short as 218 ps, pulse energy up to 250 μJ, and peak power up to 565 kW, without any switching electronics. The high output intensities of the microchip lasers enable the construction of extremely compact nonlinear optical systems capable of operating at any wavelength from 5000 to 190 nm. The short pulses are useful for high-precision ranging and 3-dimensional imaging using time-of-flight techniques. When focused, the output intensities are sufficient to photoablate materials, with applications in laser-induced breakdown spectroscopy and micromachining. The ultraviolet harmonics of the microchip laser have been used to perform fluorescence spectroscopy for a variety of applications, including environmental monitoring. Systems based on passively Q-switched microchip lasers, like the lasers themselves, are small, efficient, robust, and potentially low cost, making them ideally suited for field use.

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.

Coupled-cavity electro-optically Q-switchedNd: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.

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.

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.

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.