Positive Branch Confocal Unstable Resonator Research Articles

Intracavity adaptive correction of an unstable standing-wave resonator based on reconstruction matrix optimization.

Due to the existence of the expanding beam portion in the positive branch confocal unstable resonator, the laser passes through the intracavity deformable mirror (DM) twice with different apertures, which makes it complicated to calculate the required compensation surface of the DM. In this paper, an adaptive compensation method for intracavity aberrations based on reconstruction matrix optimization is proposed to solve this problem. A collimated probe laser of 976 nm and a Shack-Hartmann wavefront sensor (SHWFS) are introduced from the outside of the resonator to detect intracavity aberrations. The feasibility and effectiveness of this method are verified by numerical simulations and the passive resonator testbed system. By adopting the optimized reconstruction matrix, the control voltages of the intracavity DM can be directly calculated from the SHWFS slopes. After compensation by the intracavity DM, the beam quality β of the annular beam coupled out from the scraper is improved from 6.2 times diffraction limit to 1.6 times diffraction limit.

Numerical study of unstable resonator in thin disk laser

In this paper a disk laser with unstable resonator is investigated numerically. Using Collins integral and diffraction theory, a positive branch confocal unstable resonator with a thin disk shape active medium is simulated. Thermal lensing of the disk is considered in our research. Laser beam profile and output power are calculated for unstable resonator with variable internal lens. The calculations show instability of output laser beam during pump power increasing due to changes of disk dioptric power. Also calculations show that power extraction is only possible for lasers with not too thin disks.

非链式脉冲DF激光器非稳腔设计与实验研究

By employing positive branch confocal unstable resonator, design of cavity parameters and experimental research on non-chain pulsed DF laser are carried out. The advantages of suppressing divergence angle and improving beam quality are shown by comparing plano-concave stable resonator with unstable resonator. To estimate the beam quality, diffraction limit magnification is chosen as evaluating criterion, which can incarnate both the energy focusing degree and divergence angle excursion. 86.5% enveloping energy is used to define spot size, and 90-10 knife edge method is adopted to measure it. Nine sets of mirrors with different magnifications and mode volumes are tested and compared, and optimization method of unstable cavity parameters is concluded. Taking energy, divergence and diffraction limit magnification into account, the optimal parameters are M=1.89, D=40 mm. Laser beam with divergence angle of 0.74 mrad, =1.35, laser energy of 1.86 J, and peak power of 16.4 MW is obtained at these parameters.

Analysis of Maladjustment Sensitivity and Calibration Method for a Positive-Branch Confocal Unstable Resonator

The effect of intracavity aberration perturbation on output mode structure properties of unstable laser resonator is been experimentally researched using Hartmann-Shack wavefront sensor on the basis of numerical analysis. Results show that intracavity tilt aberration notablely affects outcoupled intensity distribution, but only a small intracavity tilt perturbation will not obviously augment the high-order aberrations of beam phase properties. The tilt aberration, coma aberration and astigmatism will all be brought, and also tilt aberration is the main component when intracavity mirrors have a vertical movement along the direction of optic axis. When adaptive optical elements such as deformable mirrors are adopted for intracavity aberration correction, the correction for tilt aberration should be considered firstly.

Numerical methods for solving the eigenvalue problem for a positive branch confocal unstable resonator

The resonator problem for a positive branch confocal unstable resonator reduces to a Fredholm homogeneous integral equation of the second kind, whose numerical solution here is based on a sequence of algebraic eigenvalue problems. We compare two algorithms for the solution of an optical resonator problem. These are obtained by (i) successive degenerate kernel approximation by Taylor polynomials of the Fredholm kernel and (ii) Nyström’s method with Simpson’s rule as the subordinate numerical integration method. The numerical results arising from these routines compare well with other published results, and have the added advantage of simplicity and easy adaptability to other resonator problems.

Dynamic correction of thermal focusing in Nd:YAG confocal unstable resonators by use of a variable radius mirror

Excellent beam quality and divergence stability over a wide pump power range was demonstrated in a Q-switched, Nd:YAG, positive branch confocal unstable resonator by using a one degree-of-freedom, adaptive optic. Unlike single-element flexible-membrane mirrors, the variable radius mirror (VRM) consisted of a lens and mirror, whose separation determined the VRM's effective radius of curvature. This simple method enabled low cost and efficient thermal focusing compensation. The VRM was demonstrated by producing a 300-mJ Q-switch or 1-J free-running at a beam quality factor M(2) that varied between 1.2 and 1.8 as the average output power varied between 0 and 33 W.

Simple Modification of Positive-Branch Unstable Resonator for Diffraction-Limited XeCl Laser Beam

A simple modification of the output coupler to a standard positive-branch confocal unstable resonator (PBUR) was proposed and the output characteristics were investigated and compared with those of the standard PBUR. We utilized a small convex mirror of 1.8 mm diameter as an output coupler in order to reduce the beam divergence and to eliminate the subsidiary spot caused by the Fresnel reflection effect in the standard PBUR. We obtained a single spot in the focal plane with a nearly diffraction-limited beam divergence of 0.09 mrad.

Injection Locking of a Modified-Unstable-Resonator XeCl Laser by Using a Line-Narrowed Hemiconfocal Oscillator

An injection-locked XeCl excimer laser with a modified positive-branch confocal unstable resonator was developed and the output characteristics were investigated. We utilized the hemiconfocal scheme in the line-narrowed oscillator in order to obtain a seed beam with high energy as well as narrow linewidth. In this case we obtained 0.05 cm-1 linewidth with 10 µ J output energy. The maximum output energy of the injection-locked oscillator was 110 mJ, which is 15% greater than that with free-running oscillation. We also presented a new method which can simply measure the power gain of the amplifier, by which the small signal gain coefficient of the amplifier was measured to be 10%/cm.

Diffraction-limited single-longitudinal-mode multiple-prism flashlamp-pumped dye laser oscillator: linewidth analysis and injection of amplifier system

In this paper, we present results of a study on a compact multiple-prism Littrow flashlamp-pumped dye laser oscillator. Single longitudinal mode at a linewidth </=375 MHz was achieved in a diffraction-limited laser beam with a divergence of 0.5 mrad at full angle. Output energy was 11 mJ for rhodamine 590 at a concentration of 5 x 10(-5) M. A detailed analysis of linewidth characterization is provided, and results demonstrating suppression of double-mode operation to produce single-mode oscillation are described. Also, we provide experimental evidence of linewidth variations during the laser pulse. A flashlamp-pumped positive-branch confocal unstable resonator was used to amplify the narrow-linewidth emission from the oscillator to an output energy of 600 mJ.

Experimental observation of unstable resonator mode evolution in a high-power KrF laser

For a pulsed high-power laser with unstable resonator, the mode evolution time is important from the viewpoints of beam focusability and laser-energy usefulness. We observed temporal and spatial behavior of the mode evolution in a several-tens-joule KrF laser with a positive branch confocal unstable resonator, which is pumped by electron beams with a pulse width of 65 ns (FWHM). The beam divergence angle was decreased by a factor of 1/M2 (M:magnification) per round trip in the resonator and resulted in a full angle divergence of 0.6 mrad.

Transverse mode formation time in pulsed CO 2 lasers

Transverse mode formation dynamics were analyzed using a low-magnification ( M = 1.32) positive-branch confocal unstable resonator in a high-energy pulsed CO 2 laser. The temporal behavior of mode formation was experimentally examined by observation of far-field burn pattern changes. Experiments agree with geometrical and computational results.

Picosecond high power extraction from an unstable resonator based injection-locked XeCl laser

Single pulse peak power of over 0.3 GW with good beam quality was obtained from an injection-locked XeCl laser based on a positive branch confocal unstable resonator. The high power thus obtained has the potential of generating efficient high power tunable picosecond pulses from organic dyes in the UV and near UV region of the spectrum by pumping in a synchronous scheme.

Transform-limited-bandwidth injection locking of an XeF laser with an Ar-ion laser at 3511 Å

We report attainment of transform-limited bandwidth in an XeF laser by injection locking a positive-branch confocal unstable resonator with 1 W of power from an Ar-ion laser at 3511 A. A diffraction-limited beam of >2-MW power, with a bandwidth of ~50 MHz (~1 x 10(-4) A), is generated. We find that since the XeF UV emission lines start from differentupper vibrational levels of the B state, ~40% of the B ? X energy is not available to be channeled into the locked line.

Optical extraction efficiency in lasers with high Fresnel number confocal unstable resonators

Using the formulation of Moore and McCarthy for the equation describing the dominant mode in a positive branch confocal unstable resonator in the geometrical optics limit and a simple two-level kinetics model, we analyze the dependence of the optical extraction efficiency (eta) on resonator magnification (M), length (L), small signal gain (go), and (nonsaturable) background absorption (alpha). The model has cylindrical symmetry and spatially uniform small signal gain, absorption, and index of refraction. For fixed gamma= g(0)/alpha and M, a value of g(0)L that maximizes eta is found. For different gamma, the maximum obtainable value of al is found to be independent of M and to depend upon gamma in a simple way.