Norman Hodgson

Efficient 100-W Nd:YAG laser operating at a wavelength of 1.444μm

Efficient laser emission of flash-lamp-pumped Nd:YAG rods at a wavelength of 1.444 microm is reported. A maximum average output power of 100 W at pulse energies of 5.5 J and a pulse duration of 0.65 ms was achieved. The highest electrical-to-optical overall efficiency of 1.3% was attained with a single elliptical silver pump cavity with europium-doped quartz as a spectral filter. The 1.444-microm performance as well as the output characteristics at 1.064 and 1.32 microm of Nd:YAG were investigated as a function of doping concentration and rod diameter.

Multirod unstable resonators for high-power solid-state lasers

The properties of positive-branch and negative-branch unstable resonators with variable reflectivity mirrors and several variable internal lenses were investigated both theoretically and experimentally. Design rules for optimized unstable resonators for one or more active elements are derived on the basis of the ABCD matrix formalism. Experiments were performed with a pulsed Nd:YAG system consisting of three 6 in. × 3/8 in. (15.24 cm × 0.95 cm) rods. This system provided a maximum output power of 550 W per rod when a symmetric flat-flat resonator was used. Unstable resonators achieved up to 75% of this maximum value with beam-parameter products between 2 and 10 mm mrad. The beam quality becomes worse as more active elements are used inside the resonator. This deterioration of focusability is caused by spherical aberration in combination with differences of refractive power for r and Φ polarizations.

The Fabry Perot Resonator

Whether a steady state radiation field can be established in an optical resonator depends on the wavelength of the radiation and on the mirror spacing. Steady state means that both the amplitude and the phase reproduce themselves after one round trip. It is easy to understand that both conditions can only be accomplished if the resonator length is an integral multiple of half the wavelength. Only in this case can we obtain standing waves inside the resonator with nodal intensity points on the mirror surfaces (Fig. 4.1). The preceding statement is always true as long as the field is not confined laterally by means of apertures. Hence, for a given mirror spacing L 0 and a medium with index of refraction n between the mirrors, we will find steady state field distributions for all wavelengths λ q for which the following condition holds:

Unstable multirod Nd:YAG lasers with variable reflectivity mirrors

{\lambda _q} = \frac{{2L}}{q}

Measurement of Laser Beam Parameters

(4.1) with:

Single Mode Resonators

\begin{array}{l} \lambda q:wavelength\,in\,vacuum \\ L = {L_0}n:optical\,path\,length\,between\,mirrors \\ {L_0}:geomatrical\,path\,langth\,betweenmirrors \\ n:index\,of\,refraction \\ \end{array}