Self-filtering unstable resonator operation of XeCl excimer laser

A diffraction-limited laser beam with a pulse energy of 120 mJ and brightness up to a magnitude order of 10¹⁴W . cm^-2. Sr^-1has been achieved in an X-ray preionized discharge XeCl laser by using a self-filtering unstable resonator. The near- and far-field laser properties have been examined.     

High-power CO2 laser using Gauss-core resonator for 6-kWlarge-volume TEM00 mode operation

A novel resonator based on a stable resonator configuration designed to yield a highly focusing beam operating in a large-volume TEM ₀₀ is presented. An output coupler of the new stable resonator has a circular partial-reflection region in the center that is surrounded by an antireflection region. Main-beam mode is determined by the partial-reflection region existing in the “core” of the output coupler. A diffraction beam spread from the center of the optical path in the cavity is amplified by a laser medium. By combining part of the core beam transmitted from the partial-reflection region with the amplified diffraction beam under the phase-unified condition, a diffraction-limited laser beam having a large diameter is obtained. A 6.2-kW linearly polarized output beam with the M² factor of 1.7 is obtained experimentally for a high-power CW CO₂ laser. In laser-materials processing, we can cut 1:mm thin mild steel with a cutting speed as high as 64 m/min, at 5.9 kW     

On the super-Gaussian unstable resonators for high-gain short-pulselaser media

High-mode-volume, high-energy (70-mJ), high-brightness (1.6×10¹⁴ W cm^-2 Sr^-1) laser beams have been extracted from a high-gain short-pulse XeCl laser with a super-Gaussian unstable resonator. These results are obtained by increasing the cavity magnification factor to 6.6 and the output mirror peak reflectivity to 78%. The output beam divergence is seen to decrease from an initial value of ~0.2 mrad down to nearly diffraction limited after 6 ns for the short gain build-up time of the active medium     

High-brightness CuBr MOPA laser with diffraction-limited throughout-pulse emission

CuBr master oscillator-power amplifier (MOPA) laser system fitted with a generalized diffraction filtered resonator (GDFR) is reported to produce high-quality beam of throughout-pulse diffraction-limited laser emission at the repetition rate of /spl sim/19 kHz. The comparison with typical (stable and unstable) resonator configurations for CuBr lasers has featured out its high brightness accompanied by a very low beam divergence permanent within laser pulse. This intrinsic characteristic of GDFR-MOPA laser radiation makes it a perfect light source for fine laser applications.     

Nd:YAG loop resonator with a Cr4+:YAG self-pumpedphase-conjugate mirror

We demonstrate a Nd:YAG loop resonator with a self-pumped phase conjugate, mirror in a Cr⁴⁺:YAG crystal, in the nanosecond regime. A maximum extraction of 29 mJ and a maximum reflectivity of 3.3 are obtained. The output beam is a high-quality diffraction-limited TEM ₀₀ mode and has a pulse shape of ~20-ns duration, showing the self Q-switching ability of the resonator. In addition, we demonstrate an original and specific configuration of the anisotropic Cr⁴⁺:YAG crystal that compensates not only for phase aberrations but also for polarization aberrations induced into the loop resonator     

Short-pulse, eye-safe Nd:YAG laser using cavity-dumping

A short-pulse 1.444-μm laser based on Nd:YAG technology has been demonstrated. The 1.444-μm is eye-safe. With the cavity-dump technique, a pulse of 50 m× and 14 ns was obtained. The beam quality was excellent with an M² of 1.6 by the use of a telescopic resonator. Silicon-window polarizers were used to suppress the 1.06-μm radiation but showed 1.444-μm absorption as well     

Self-mode-locked unstable resonator copper vapor laser

We have studied a copper vapor laser equipped with unstable resonator optics and an intracavity beam splitter. The magnification of the present resonator configuration is as high as 60, and single transverse mode operation is practically supported in this system. We report on the laser output with near diffraction-limited beam divergence and a new observation of self-mode-locking behavior in the output pulses     

A double-ended, unstable resonator submillimeter laser

The characteristics of a pulsed, methyl fluoride laser utilizing a novel, double-ended unstable resonator are described. The design incorporates an intracavity, double-faced scraper mirror to produce separate input/output ports for CO2pump laser excitation and submillimeter laser output. Experimental results show that this configuration achieves state-of-the-art conversion efficiency and diffraction-limited beam quality.     

High power and high focusing CWCO2 laser using anunstable resonator with a phase-unifying output coupler

A high-power and high-focusing continuous-wave (CW) CO₂ laser with a novel unstable resonator was developed. This resonator contains a step-wise variable reflecting output coupler named the phase-unifying output coupler and a total reflector. The laser was excited by a capacitive-barriered AC discharge called a silent discharge. A linearly polarized laser beam with a diffraction-limited divergence angle of 0.55 mrad was obtained. Very stable CW laser operation at an output power of 5 kW was achieved with a threshold discharge power of 10 kW and a slope efficiency of 18%     

Characterization of an ultrahigh peak powerXeF(C→A) excimer laser system

The gain characteristics of an electron-beam pumped XeF(C→A) excimer amplifier operating in the blue-green spectral region were investigated for several laser pulse lengths. Saturation energy densities of 50 and 80 mJ/cm² were measured for injected laser pulse durations of 250 fs and ~100 ps, respectively. A gain bandwidth of 60 nm was observed with ~100-ps pulse injection. Using an optimized unstable resonator design, the laser amplifier has produced 275-mJ pulses with a pulse duration of 250 fs and a 2.5 times diffraction-limited beam quality, making the XeF(C→A) amplifier the first compact laser system in the visible spectral region to reach peak powers at the terawatt level     

Beam deflection in a transverse-flow gas laser

The beam deflection phenomenon of a transverse-flow discharge-excited CO₂ gas laser is studied by measuring the beam pattern with the rotating-wire method at gas velocities of 35-70 m/s, gas pressures of 5.3-10.6 kPa (10³ N/m²), and laser powers of 50-700 W. The beam deflection distance increased with increasing laser power and gas pressure and with decreasing gas velocity. All the data points of beam deflection distances observed experimentally fell on one line when normalized by the gas pressure and plotted against the measured temperature gradient in the resonator. It is shown that the most important factor affecting the beam deflection is the refractive index variation of the gas produced by the gas temperature gradient in the resonator. Methods to reduce the beam-deflection distances are suggested     

具有二维变反射率输出镜的谐振腔设计研究

文中报道了用于高平均功率板条状工作物质激光器的谐振腔设计,该设计采用非稳定腔方案,输出耦合镜具有二维变反射率分布反射膜,在腔内补偿了工作物质引起的像散。得到了千瓦级的输出,光束质量优于3倍衍射极限。     

Novel large mode volume resonator

A resonator in which the dominant mode-shaping effect is diffraction from an undersized aperture is reported. The result is a large mode volume and a near diffraction-limited Gaussian output beam. The alignment sensitivity is similar to that of a positive branch unstable resonator, although the mirror configuration can vary over a large range in either the geometrically stable or unstable regimes. A pulsed Nd:YAG laser using this resonator was built and characterized in the free-running, Q-switching, and mode-locking regimes, and as a regenerative amplifier     

Thermal lens and beam properties in multiple longitudinally diodelaser pumped Nd:YAG slab lasers

The focal length of the thermal lens and the beam quality factor (beam propagation factor) M² for a multiple longitudinally diode pumped slab laser is deduced for pump and output powers up to 16 and 4.5 W, respectively. Due to the geometry of the arrangement, a stronger thermal lens is observed in the plane with the larger pump spot radius as predicted by an analytical model for slab geometries. In addition, the second stable zone of an asymmetric resonator is found to be advantageous for improved beam properties at high output powers     

GaInAsSb-AlGaAsSb tapered lasers emitting at 2.05 μm with 0.6-Wdiffraction-limited power

Tapered lasers fabricated from a GaInAsSb-AlGaAsSb single-quantum-well structure are reported. The laser structure, grown by molecular beam epitaxy, has broad-stripe pulsed threshold current densities as low as 50 A/cm² at room temperature. Tapered lasers have exhibited diffraction-limited continuous-wave output power up to 600 mW     

Hooting modes in a CO2 waveguide laser

CO₂ waveguide lasers `hoot' when, instead of the solitary resonator mode expected from a homogeneously broadened gas laser, two or more resonator transverse modes laser simultaneously on a common laser line. The unwanted mode or modes, even if very faint and present only occasionally, can impede heterodyne measurements where a clean frequency spectrum is required. The authors report measurements of transverse-mode beat frequencies from a small RF-excited CO₂ laser with a hybrid Al/Al₂O₃ square-bore waveguide and plane mirrors; these frequencies alter with mirror tilt by up to 70 MHz mrad^-1. A minimum beat frequency is seen when the laser is well assigned. The authors suggest that a model of the misaligned resonator may help to identify the faint modes responsible for hooting     

High power, nearly diffraction-limited output from a semiconductorlaser with an unstable resonator

The authors describe an on-the-chip design of a nearly diffraction-limited broad-area semiconductor diode laser. The device achieved single lateral mode operation as unstable resonators with magnifications between two and three. The unstable resonators were realized by focused ion beam (FIB) micromachining a diverging mirror at one of the outcoupling facets. The modeling efforts agree well with experimental data and show that an optimum device design exists in which stable nearly diffraction-limited operation is predicted for up to six times threshold. This unstable resonator design has achieved, experimentally, the highest diffraction limited power and best external differential efficiency ever reported for any broad-area device with a curved facet     

Properties of an unstable confocal resonator CO2laser system

The results of an experimental and theoretical study of the properties of a confocal unstable resonator used with a conventional CO2-N2-He laser operating at 10.6 μ are presented. Measurements were made of the near- and far-field intensity distribution of the aligned resonator for Fresnel numbers of 3.7, 6.1, and 7.1. Fundamental mode operation was achieved in all cases. Beam steering and mode degradation associated with mirror misalignment were also studied experimentally. Suitable geometric models have been developed to account for 1) the sensitivity of the resonator output coupling and center far-field intensity to variations in the resonator length and mirror curvatures, and 2) the sensitivity of the beam direction and power to angular misalignment of the mirrors.     

Theoretical high-efficiency extraction study of a short-pulseelectron-beam-pumped ArF laser amplifier with atmospheric pressureAr-rich mixtures

The single-pass (50 cm) amplifier performance of an atmospheric-pressure ArF laser pumped by a 65-ns full-width-at-half-maximum short-pulse electron beam was investigated theoretically for a wide range of excitation rates (0.1-2.0 MW/cm³ ). Atmospheric mixtures of Ne, Ar, and F₂ (three mixtures of Ar=40%, 70%, and Ne-free) were studied. A kinetic numerical model of the ArF amplifier with a Ne buffer system was constructed. A one-dimensional propagation treatment considered the gain depletion and saturation absorption spatially and temporally along the optical axis. In this model the rate constants for electron quenching of ArF* of 1.6×10^-7, 1.9×10^-7, and 2.4×10 ^-7 cm³/s were used for Ar concentration of 40, 70 percent, and Ar/F₂ mixture, respectively     

Laser frequency control using an optical resonator locked to anelectronic oscillator

A new method for controlling a laser's center frequency is reported. This method extends the Pound-Drever-Hall technique, which delivers exceptional laser linewidth. The new technique, applicable over a broad range of wavelengths, produces a laser beam with both narrow linewidth and stable center frequency. A diode-pumped ring laser is locked to an ultrahigh-finesse, tunable optical resonator which, in turn, is locked to an electronic (5 MHz) oscillator using a difference frequency developed by locking a second laser to the resonator. A 1064-nm beam is reported with linewidth less than 0.004 Hz and center-frequency stability given by the electronic reference. For the case of an oven-controlled quartz crystal, the laser center-frequency stability is less than 1 part in 10¹¹ per day with root Allan variance of 10^-12 for a 1000-s time delay. The entire system is compact, and all elements are solid-state, making it useful both in the laboratory and in a number of space-based applications