Laser Resonator Mirrors Research Articles

X-ray laser resonator for the kilo-electron-volt range

We have designed, constructed, and tested an x-ray laser resonator operating in the hard x-ray, keV energy region. This ring x-ray laser cavity is formed by four highly oriented pyrolytic graphite crystals. The crystals are set at the Bragg angles that allow for the complete 360° round trip of the 2.37 Å, 5.23 keV Lα line of neodymium. In addition, we also present experimental data of a similar ring laser resonator that utilizes the Cr Kα, 5.41 keV, x-ray line to propagate through the four mirrors of the cavity. The specific properties of these x-ray laser resonator mirrors, including reflection losses and cavity arrangement, are presented.

Power-scaled Pr:YAlO3 laser at 747 and 720 nm wavelengths

We report efficient continuous-wave laser operation of a laser-diode pumped Pr:YAlO3 crystal in a power-scaled resonator arrangement. Using two pumping GaN-laser diodes emitting at 448 nm wavelength with maximum output power of 1 W each and a 5 mm long Pr(0.6 at.%):YAlO3 crystal, 290 mW of output power in the near-infrared spectral region (747 nm) with an oscillation threshold of about 500 mW has been reached. The maximum absorbed pump power was ≈1.5 W, resulting in the slope efficiency of 28%. Moreover, laser emission at two transitions in the visible part of the electromagnetic spectrum (747 and 720 nm) has been demonstrated employing the broadband laser resonator mirrors in connection with the tuning element (Lyot filter).

Design of semiconductor laser resonator mirrors for optimal second-harmonic generation

The waveguide second-harmonic generation is a reliable mechanism for frequency doubling of laser emission since light can be highly confined to a nonlinear waveguiding medium, besides being compatible with current present semiconductor and solid state lasers. An optimization is achieved based on designing the resonator mirror reflectivity at the fundamental and the second-harmonic wavelengths to obtain optimal trapping and optical losses of the fundamental and the second-harmonic waves inside the resonator.

Efficient diode-pumped passively Q-switched laser operation around 1.9 μm and self-frequency Raman conversion of Tm-doped KY(WO4)2

Passively Q-switched operation of Yb,Tm:KY(WO4)2 and Tm:KY(WO4)2 lasers diode pumped at 805 nm has been investigated. A thin plate of Cr:ZnS was used as a saturable absorber for passive Q switching. A maximum average output power of 116 mW emitted at 1.9 μm in comparison to 160 mW for the free-running regime at the same pumping level has been obtained with a slope efficiency of 26% with respect to the incident pump power. Using a Tm:KYW sample with broadband antireflection coatings and dichroic laser resonator mirror, the first Stokes component of Raman self-frequency conversion was observed at 2365 nm.

NONLINEAR OPTICAL RESPONSE OF CYANOBIPHENYL LIQUID CRYSTALS TO HIGH-POWER, NANOSECOND LASER RADIATION

Results from investigations are summarized into: (1) transient refractive and absorptive (two-photon) nonlinearities at 0.532 μm by the Z-scan method, and (2) reflective nonlinearity in the near-IR, of linearly nonabsorbing cyanobiphenyl liquid crystals under nanosecond laser irradiation. (1) For isotropic liquid crystals at the several-nanosecond time scale and several tens-micrometers beam-waist-diameter, transient molecular-reorientation and thermal/density refractive nonlinearities compete in changing the sign of the total transient refractive nonlinearity. For the different, given pulse durations, the influence of coupled thermal and density effects on nonlinear refraction depends, through buildup time, on the beam-waist diameter. Nonlinear absorption coefficients depend on the incident intensity. For planar nematic layers, cumulative effects in heating (and in refractive nonlinearity) were observed even at low, 2–10 Hz pulse repetition rate. These results are useful for optical power limiting applications, and for intensity and beam-quality sensors of pulsed, high-power lasers. (2) Reflective nonlinearity of chiral-nematic (cholesteric) mirrors near selective reflection conditions for circular polarized light at λ=1.064 μm was studied both under free space irradiation and inside a laser resonator. Specially chosen experimental irradiation conditions make it possible to attribute the observed changing of reflectivity to athermal helix unwinding by the optical field. The results can find applications in laser-resonator mirrors, Q-switches and soft apertures for beam-profile formation, and also in showing the limits of use cholesteric optical elements in high-power laser beams.

Qswitch and longitudinal modes of a laser oscillator with a stimulated-Brillouin-scattering mirror

A hypersound wave grating generated by stimulated-Brillouin-scattering (SBS) is applied in a laser resonator as a nonlinear mirror. This self pumped SBS mirror can be used for a passive Q switching of the laser by operating it inside a starter cavity. The Q-switch energy and pulse duration can be varied with a neutral glass filter. The Q-switch mechanism is explained and the pulse energy is calculated. As a consequence of the Brillouin frequency shift such resonators show a special behavior of the longitudinal modes. The longitudinal modes and the corresponding pulse shape of such a laser are investigated experimentally as a function of the start resonator length and the position of the SBS mirror. The results are explained by a superposition of modes of the SBS resonator taking into account their phases. Finally, the spectrum of the longitudinal modes is shown to be time dependent. These investigations yield in design criteria for efficient application of SBS mirrors as a laser resonator mirror.

Sub-Poisson statistics of the radiation emitted by a feedback laser

An analysis is made of the model of a single-mode semiconductor injection laser with a feedback loop based on amplitude fluctuations. It is shown that radiation in the sub-Poisson photon statistics can be coupled out from such a laser if a second laser-resonator mirror, which is not in the feedback loop, is used as the exit mirror.

New mirror for a laser resonator

A new laser resonator mirror is proposed. It consists of several nonparallel planes, which make it possible to increase the homogeneity of the distribution of the intensity over the laser beam cross section and to reduce its divergence. The results are reported of the use of such a mirror at the exit from a solid-state laser.

Absorption bistability in evaporated ZnSex thin films

Intrinsic absorption bistability in ZnSe1.36 thin films, produced by thermal evaporation is observed. The influence of laser pulse duration and resonator mirror reflectivity is studied experimentally and theoretically. Compared to ZnSe elements prepared by other methods, the evaporated films allow a longer operation wavelength of 514 nm, a low threshold power of 10 mW and a smaller element size below 10 μm3.

Diamond Turning of Optics

Recent developments in diamond turning of optics are reviewed. Improved surface figure and surface finish have been achieved as well as metrology of the machined part. Reflectivities of diamond turned metals at various wavelengths are summarized. Application of diamond turned optics include laser resonator mirrors, x-ray microscopes, x-ray telescopes, missile optics, and scanner mirrors. The technology looks especially promising for present infrared requirements since both reflective, refractive, and transmittive components can be fabricated. Diamond turning of optics can be defined as the use of a diamond tool on a precision lathe under very precisely controlled machine and environmental conditions to fabricate a finished optical component. The specific application of precision machining principles to diamond turning has been led by the Lawrence Livermore Laboratory (LLL), Livermore, California and Union Carbide Y-12 Plant (Y-12), Oak Ridge, Tennessee.

The appearance of angular oscillation modes with tilting of a laser resonator mirror

The appearance of angular oscillation modes with tilting of a laser resonator mirror

Determination of the boundary losses in lasers

A breakdown of the detrimental loss factor of a laser into losses within the rod (due to scattering and inactive absorption) and boundary losses (the losses in the resonator due to divergence of the laser beam) is suggested. Formulas are derived for taking account of the boundary loss factor by introducing the effective reflection coefficient of the laser resonator mirrors. The theoretical and experimental relations for variations in the boundary losses resulting from increases in resonator length are compared. It is shown that the boundary losses represent the major portion of the total detrimental losses in a laser.