Massachusetts Institute of Technology

United States of America As Represented by the Secretary of the Air Force

Tso Yee Fan

Antonio Sanchez-Rubio

Bien Chann

Steven J Augst

James N Walpole

James R Leger

Richard C Williamson

William C Goltsos

Anish K Goyal

Ivars Melngailis

Daniel J Ripin

Franz Xaver Kaertner

Thomas H Jeys

Juan Montoya

Hong K Choi

Peter A Schulz

Han Q Le

Stephen J Eglash

Kyung-Han Hong

C David Nabors

Edilson L Falcao-Filho

Philip Lacovara

Chien-Jen Lai

John Hybl

A laser system comprises: a seed oscillator, having a seed output; dispersive optics, operative to receive the seed output and divide the seed output into spectrally separate seed components; an array of individually addressable, phase adjustable laser amplifiers corresponding to the spectrally separate components, each laser amplifier receiving as its seed one of the spectrally separate seed components and producing one of the spectrally separate amplified components; and phase actuators controlling the individually addressable, phase adjustable laser amplifiers. A method of operating a laser system comprises: generating a seed signal; dividing the seed signal into spectrally separate component signals; amplifying the spectrally separate component signals; recombining the spectrally separate component signals into an amplified output; and controlling phases of the amplified spectrally separate component signals. Both single-pass and double-pass amplifier array versions are disclosed.

Continuous wave or ultrafast lasers

A method and apparatus for two-dimensional wavelength beam combining of laser sources. In one example, an external cavity multi-wavelength laser includes an array of laser emitters each producing an optical beam having a specified wavelength, a grating stack comprising a plurality of first-order diffraction gratings arranged linearly in a first dimension, and a dispersive element. The laser further includes a cylindrical telescope that images the optical beams from the array of laser emitters onto the grating stack. A first cylindrical transform lens spatially overlaps the optical beams in a second dimension forming a first region of overlap at the grating stack. A second cylindrical transform lens spatially overlaps the optical beams from the grating stack in the first dimension forming a second region of overlap at the dispersive element. The dispersive element transmits a multi-wavelength output beam comprising the spatially overlapped optical beams from the array of laser emitters.

Two-dimensional wavelength-beam-combining of lasers using first-order grating stack

A method and apparatus for providing a high peak power optical beam. The method includes interleaving pulse trains of different wavelengths and spatially and temporally overlapping the different wavelengths to produce an amplified output beam with very high peak power.

High peak power optical amplifier

Coherent beam combining of laser gain elements achieves high output power in a diffraction limited beam. An active beam combining system coherently combines optical beams emitted by semiconductor laser gain elements in an external resonant cavity configuration. A beam combiner in the resonant cavity combines the outputs of the laser gain elements into a single coherent output beam whose power is monitored by a photodetector. A processor uses the photodetector's output to adjust the phases of the respective optical beams emitted by the laser gain elements so as to increase or maximize the coherent output beam's power. The processor may vary the optical beams' phases according to a stochastic parallel gradient descent (SPGD) algorithm for active phase control. Experimental results show a beam combining efficiency of 81% with an upper limit of 90% or higher and without the scaling limits imposed on passive-phasing systems.

Methods, systems, and apparatus for coherent beam combining

Stimulating emission via thulium's lasing transition from theHmanifold to theHmanifold yields light at wavelength of about 820 nm. Unfortunately, excited thulium ions also transition from theHmanifold to the long-livedFmanifold, where they become trapped and can no longer participate in the lasing transition. If the enough of the thulium population becomes trapped in theFmanifold, the gain medium becomes transparent at the pump wavelength, rendering population inversion difficult or impossible. Fortunately, the size of the population in theFmanifold can be limited by selecting an appropriate crystal host and thulium doping concentration, pumping the thulium with pulses shorter than theFmanifold's lifetime, cooling the gain medium to low temperature (e.g., 77 K), stimulating emission from theFmanifold, upconversion pumping of the thulium from theFmanifold to theHmanifold, or transferring energy from thulium in theFmanifold to a co-dopant.

Thulium laser

Extreme ultraviolet radiation is generated based on high-order harmonic generation. First, a driver pulse is generated from a drive laser. Second, the infrared driver pulse is passed through a second harmonic generator with an output wavelength in the range from 400 to 700 nm. Third, the pulse is then passed through a gas medium, which can be inside a resonant cavity, to generate a high-order harmonic in the form of extreme ultraviolet radiation.

Efficient high-harmonic-generation-based EUV source driven by short wavelength light

An external-cavity one-dimensional multi-wavelength beam combiner that performs wavelength beam combining along a stacking dimension of a laser stack formed of a plurality of laser arrays, each laser array configured to generate optical radiation having a unique wavelength, and each of the plurality of laser arrays including one or more laser emitters arranged along an array dimension of the laser stack. The multi-wavelength beam combiner includes an optical imaging element configured to image each of the laser emitters along a slow axis of the laser emitters, an optical focusing element arranged to intercept the optical radiation from each of the plurality of laser arrays and combine the optical radiation along a stacking dimension of the laser stack to form a multi-wavelength optical beam, and a diffraction element positioned at a region of overlap of the optical radiation to receive and transmit the multi-wavelength optical beam.

External-cavity one-dimensional multi-wavelength beam combining of two-dimensional laser elements

A solid-state gain element including a thin doped region in which an optical signal propagates through the thin doped region at a large angle with respect to the normal to the thin doped region, reflects at a boundary of the thin doped region, and passes through the thin doped region again. An optical pump beam propagates through the thin doped region also at a large angle with respect to the normal to the thin doped region. In one example, the gain element and source of the pump beam are configured such that there is total internal reflection of the pump beam at the boundary of the thin doped region for a second pumping pass through the thin doped region. In another example, an elliptically symmetric laser beam is used to create a circularly symmetric gain region in the thin doped region.

Grazing-incidence-disk laser element

An external-cavity one-dimensional multi-wavelength beam combiner that performs wavelength beam combining along a stacking dimension of a laser stack formed of a plurality of laser arrays, each laser array configured to generate optical radiation having a unique wavelength, and each of the plurality of laser arrays including a plurality of laser emitters arranged along an array dimension of the laser stack. The multi-wavelength beam combiner includes a cylindrical telescope configured to image each of the laser emitters along a slow axis of the laser emitters, a transform lens arranged to intercept the optical radiation from each of the plurality of laser arrays and combine the optical radiation along a stacking dimension of the laser stack to form a multi-wavelength optical beam, and a diffraction element positioned at a region of overlap of the optical radiation to receive and transmit the multi-wavelength optical beam.

A laser difference frequency discriminator that detects the difference between two laser frequencies and outputs a voltage near baseband that is related to the difference frequency. This discriminator power splits a laser beam containing the two laser frequencies into two paths, one which is sent down a delay line to a photo detector while the other is sent directly to a photodiode; there may be an optional phase shifter in either path. The relative phases of the heterodyne signals from the photo detectors are compared in a phase detector, its output voltage is related to the phase difference, which is, in turn, related to the difference frequency. This discriminator has applications in microwave generation, laser radar, and optical communications.

Laser-difference-frequency discriminator

A laser transmitter capable of transmitting large numbers of WDM channels but requiring locking of only a single channel. Each of the channels can be individually modulated using an external modulator.

Multichannel laser transmitter suitable for wavelength-division multiplexing applications

An external-resonator laser system having multiple laser elements is configured to permit each laser to undergo individual amplification notwithstanding optical beam combination. In this way, overall output power may be scaled in a desired fashion, depending on the selected characteristics of the optical amplifier elements. To achieve additional power, each of the amplifiers may implemented as a phased array. Viewed more generally, a phased-array configuration affords beam combining in two stages, with each contributing input source itself composed of multiple sources whose outputs have been combined. If each phased-array source emits at a different wavelength, this design offers a multi-wavelength output whose power level may be scaled in accordance with the number and character of the devices forming each phased array.

High power, spectrally combined laser systems and related methods

A free space external cavity multi-wavelength laser that includes a free space external cavity and a two-dimensional laser array is described. The two-dimensional laser array includes a plurality of optical gain elements where each optical gain element generates optical radiation having a unique wavelength and a unique free space optical path. The laser also includes a two-dimensional dispersive optical system that spatially and angularly overlaps each of the free space optical paths in two dimensions. The laser also includes a partially reflecting element that is positioned to intercept each of the free space optical paths. The partially reflecting element, a reflector on each gain element, and the two-dimensional dispersive optical system together form a free space laser cavity that defines the unique wavelengths. The partially reflecting element transmits an overlapping beam comprising radiation having the unique wavelengths.

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Belmont, MA, United States of America

Tso Yee Fan