Efficient beam shaping of linear, high-power diode lasers by use of micro-optics

Abstract

We have designed, fabricated, and characterized a micro-optical beam-shaping device that is intended to optimize the coupling of an incoherent, linearly extended high-power diode laser into a multimode fiber. The device uses two aligned diffractive optical elements ͑DOEs͒ in combination with conventional optics. With a first prototype, we achieved an overall efficiency of 28%. Straightforward improvements, such as antireflective coatings and the use of gray-tone elements, are expected to lead to an efficiency of approximately 50%. The device is compact, and its fabrication is suited for mass production at low cost. This micro-optical device, used in a range-finder measurement system, will extend the measurement range. In addition to the direct laser writing technique, which was used for fabrication of the DOEs of the prototype, we applied two other technologies for the fabrication of the micro-optical elements and compared their performance. The technologies were multiple-projection photolithography in combination with reactive-ion etching in fused silica and high-energy beam-sensitive glass gray-tone lithography in photoresist. We found that refractive-type elements ͑gray tone͒ yield better efficiency for large deflection angles, whereas diffractive elements ͑multilevel or laser written͒ give intrinsically accurate deflection angles.

Direct-Write Photolithography for Cylindrical Tooling Fabrication in Roll-to-Roll Microcontact Printing

“…This distribution then depends on the specific light source in use. The intensity distribution of the focused diode laser used in the apparatus is modeled as a Gaussian distribution [21,22], and in the 2D reference frame of Fig. 4 this is simplified to…”

Diffractive wavefront correction of remote sensing systems based on pulsed laser diodes

“…where: A(x/l,y/l) defines field amplitude in the exit pupil, A 0 /l 2 is the area of the exit pupil in units of (wavelength) 2 . It should be mentioned, that the optical field corresponds to a complex function which in the target plane is determined by A (PSF) and j (PSF) concerning its real amplitude and real phase, respectively.…”

“…Such technologies, like time−of−flight (TOF) range−finding, handheld speedometry of vehicles, terrain scanners, airbor− ne profilometry of the ground, free space optical communi− cation systems, weapon laser simulators, laser illuminators, friend−or−foe interrogators and others should be mentioned in this context. In the configurations requiring large range of operation, at the level of several kilometers, it is necessary to apply high−power pulsed lasers, which in terms of optical performance cannot be treated like spatially coherent sour− ces [1,2]. In this aspect they tend to be more similar to light emitting diodes (LED) than to what is commonly perceived as a laser.…”

Beam forming optic aberrations’ impact on maximum range of semiconductor laser based rangefinders

“…Active structure of high−power pulsed semiconductor lasers widely used in mid−range modules consist of several light emitting stripes [7], located on one or more chips as presented schematically in Fig. 2.…”