Diffraction-limited Beam Divergence Research Articles

On-chip platform for a phased array with minimal beam divergence and wide field-of-view.

Current silicon photonics phased arrays based on waveguide gratings enable beam steering with no moving parts. However, they suffer from a trade-off between beam divergence and field of view. Here, we show a platform based on silicon-nitride/silicon that achieves simultaneously minimal beam divergence and maximum field of view while maintaining performance that is robust to fabrication variations. In addition, in order to maximize the emission from the entire length of the grating, we design the grating's strength by varying its duty cycle (apodization) to emit uniformly. We fabricate a millimeter long grating emitter with diffraction-limited beam divergence of 0.089°.

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.

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.

Possibilities for correcting aberrations of imaging laser systems by phase conjugation

The reported method of using phase conjugation to correct distortions induced by projection optics was realized experimentally. In particular, the method was used on a low-quality 50-cm-diameter objective mirror to form laser radiation with a near diffraction-limited beam divergence of 2.4 × 10(-6) rad. The method could be applied to high-resolution imaging of objects in coherent light.

Recent advance to 3 × 10^−5 rad near diffraction-limited beam divergence of dye laser with transverse-discharge flash-lamp pumping

A new experimental setup of a Rhodamine 6G dye laser with a transverse-discharge flash-lamp-pumping system is presented. It differs from a previous setup [Sov. J. Quantum Electron. 16, 468-471 (1989)] in that it has a larger laser beam aperture (32 mm) and higher pumping energy (1 kJ), which made it possible to test the scalability and reach near diffraction-limited laser beam divergence of 3 × 10(-5) rad FWHM at beam energy 1.4 J. The effect of spectral dispersion in the active medium and of other optical elements on the beam divergence is also discussed.

Gallium phosphide microlenses by mass transport

Arrays of high quality refractive microlenses have been formed in GaP substrates by mesa etching followed by a heat treatment in which the multistep mesas were smoothed due to surface energy minimization. A smooth lens surface and an accurately controlled lens profile have been obtained. Microlenses of 130 μm diameter and 200 μm focal length have been used to collimate the outputs of GaInAsP/InP and GaAs/GaAlAs diode lasers and have yielded a nearly diffraction-limited beam divergence of 0.68°.

Flashlamp-pumped liquid laser with a diffraction-limited beam divergence of 9 × 10−5rad

An output beam having a divergence 0.5E = 9 × 10−5 rad at half-energy and a total beam energy of 0.7 J was obtained from a laser utilizing a solution of rhodamine 6G in ethanol excited by a flashlamp with a transverse discharge of 250-ns duration. An unstable telescopic resonator in the positive branch with a magnification of 3 was used to achieve this divergence, which corresponded to the diffraction limit at the laser exit aperture.

Large-numerical-aperture InP lenslets by mass transport

Lenslets with diameters up to 130 μm and numerical apertures of 0.39–0.75 have been formed in InP substrates by using mass transport to smooth out chemically etched multilevel mesa structures. The lenslets show a smooth surface with an accurately controlled profile (i.e., curvatures) and are capable of forming clear images. Some lenslets (with a diameter of approximately 67 μm) have been used to collimate the output of a buried-heterostructure diode laser (of 1.3 μm wavelength) and resulted in a nearly diffraction-limited beam divergence of 1.4°.

Single-state high-beam-quality XeCl laser with a phase-conjugate Brillouin mirror

A single-stage high-beam-quality XeCl laser, consisting of an oscillator and a double-pass amplifier with a phase-conjugate Brillouin mirror with no optical coupling between the oscillator and the amplifier, is discussed. Maximum output energy of 20 mJ with a pulse duration of 13 ns full width at half maximum has been obtained with a 0.0015-AA (469-MHz) linewidth, 1.2*diffraction-limited beam divergence from a circular 8-mm diameter beam. >

Efficient long-pulse operation of a capacitor-transfer-type XeCl laser with automatic UV preionization scheme and its line-narrowing.

Efficient long-pulse operation of a capacitor-transfer-type XeCI laser with automatic UV preionization has been demonstrated by using a pulse forming network (PFN) in a secondary capacitor circuit. Long-pulse operation with a pulse width of 80 ns full width at half maximum was achieved with an overall efficiency of 2.0% and specific energy of 1.6 Jl-1 atm-1. We have also achieved spectral narrowing to a 0.0015 A linewidth with an output energy of 400 μJ and with diffraction limited beam divergence using a grating and etalon combination.

Stability of the emission from fast-flow gas discharge industrial CO2lasers (review)

An analysis is made of the possible physical and technical reasons for fluctuations of the power and spatial emission characteristics of fast-flow gas discharge industrial CO/sub 2/ lasers caused by instabilities of the properties of the active medium and of the resonator, and by the influence on the resonator operation of processes occurring on and near a target irradiated with the laser. It is shown that the amplitude of the power fluctuations can reach 100%, while the instability of the angular distribution can exceed the diffraction-limited beam divergence. The frequency spectrum of the variation in the laser emission parameters lies in the range 10/sup -3/ to 10/sup 6/ Hz. Fluctuations having such amplitude and frequency characteristics can strongly influence the stability of an industrial process during laser processing of materials, and they must therefore be taken into account when selecting the laser equipment and its operating regimes.

Ultranarrow linewidth, magnetically switched, long pulse, xenon chloride laser

A spectral linewidth of <7×10−4 A and diffraction-limited beam divergence has been obtained from a long pulse, electric discharge xenon chloride laser with intracavity Fabry–Perot etalons. A gain duration of 100 ns provided for multipass operation of the etalons, significantly improving both contrast and finesse. The electrical discharge circuit required to produce this long gain duration was comprised of a pulse forming network, saturable inductor magnetic switch, and a tapered, constant impedance, interface transmission line.

Theory of the effect of third-harmonic generation on three-photon resonantly enhanced multiphoton ionization in focused beams

Multiphoton ionization in the region near a three-photon resonance is treated for focused, plane-polarized Gaussian beams with diffraction-limited beam divergence. In this situation, a third-harmonic field is generated within the laser beam. At, and very near, three-photon resonance the driving rate for the upper-state probability amplitude due to one-photon absorption of third-harmonic light becomes nearly equal to the corresponding three-photon rate due to the laser field, but these effects are 180\ifmmode^\circ\else\textdegree\fi{} out of phase. As a consequence of this cancellation between two pumping terms, the three-photon resonance line essentially disappears at moderate concentrations and the observed ionization has a line shape that is close to the phase-matching curve for third-harmonic generation. The ionization signal, near but not on the resonance, is due almost entirely to absorption of third-harmonic photons plus other laser photons; three-photon resonantly enhanced multiphoton ionization by the laser is much weaker. This is particularly true on the blue side of the three-photon resonance at detunings where phase matching occurs. The problem is treated quite generally with predictions of the full line shape for $n$-photon ionization and third-harmonic light generation near three-photon resonance, including the rather strong influences of positively dispersive buffer gases. We also show that the cancellation between the one-photon and the three-photon process is partially spoiled in the presence of a counterpropagating beam at the same frequency.

Miniature TEA nitrogen laser with diffraction-limited sub-nanosecond output pulses

The application of confocal unstable resonators to miniature atmospheric pressure nitrogen lasers is described. Sun-nanosecond laser pulses with diffraction-limited beam divergence were obtained from a 12.5 mm long discharge. The brightness in the diffraction-limited beam is 2.2*1017 m-2 sr-1.

Deuterium fluoride chemical laser with diffraction-limited beam divergence

An investigation was made into the possibility of achieving the diffraction-limited beam divergence from a pulsed flashlamp-pumped DF chemical laser on replacing its plane resonator with an unstable resonator of the telescopic type. Under the optimal operating conditions of the laser with the unstable resonator, a beam divergence of θ(1/2)E = 70 μ rad was obtained (practically equal to the diffraction limit) with quite a high energy efficiency (~60%) relative to that of a similar laser having a plane resonator. It was found experimentally that by appropriately detuning the unstable resonator one could make measurements of the radiation energy distribution in the far-field zone without employing additional focusing elements.

An excimer laser pumped atomic iodine laser emitting pulses in the range of 2–12 ns

An iodine photodissociation laser is pumped with a laser pulse from a XeCl or a KrF laser. Single smooth laser pulses with a duration variable from 2.6 to 12 ns are emitted by the iodine laser. A pulse power of 0.5 MW is obtained with diffraction limited beam divergence.