Research

Professor Marciante's research group is currently focused on large-mode area fibers, kW-class CW and ultrafast fiber lasers, ceramic laser materials, high-brightness semiconductor lasers, and spatially-coherent beam combination.

The word cloud generated from our journal paper titles is shown below (courtesy of Wordle): click for full-scale image

A few of our current projects are listed below.  Please also refer to our recent publications.


Large-Mode-Area Fiber Lasers

High power and high pulse energy fiber lasers and amplifiers require large-mode area fibers to spread the optical power and reduce the optical intensity to avoid detrimental noniear effects, such as stimulated Brillouin scattering.  However, modal discrimination in large-mode-area fibers becomes increasingly difficult with increasing core area.  Moreover, effects such as bend-induced mode compression and thermal mode instability further inhibit core-area scaling.

We are developing multiple types of fibers to mitigate these problems and enable core-area scaling while maintaining good beam quality.  Such fiber types include semi-guiding high-aspect-ratio-core (SHARC) fiber, confined-gain fiber to exploit gain filtering, and other unique designs employing spatial index and gain tailoring.

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Engineered Fiber to Mitigate Thermal Mode Instability

One of the most detrimental problems in power-scaling continuous-wave fiber lasers is thermal mode instability.   As the optical power increases to hundreds of watts, the energy difference between the pump and signal photons, known as the quantum defect, induces thermally induced refractive index changes as the optical power increases to hundreds of watts.  Since the spatial modes each propagate down the fiber with different speeds, their combined intensity profile extracts the gain in a periodic fashion, and the resulting thermal index profile is periodic.  This index grating couples power between the spatial modes of the fiber, resulting in runaway beam degradation.

To solve this problem, we are currently exploiting the mathematical similarities between electronic quantum wells ("particle in a box") and optical waveguides.  Our findings have led to large-mode-area fiber designs that have significnatly increased (5-10x) higher threshold before the onset of thermal mode instability.


Multi-kilowatt Femtosecond Fiber Lasers

Femtosecond lasers have demonstrated a multitude of material procesing techniques.  However, the limited power of such lasers makes cost-effective commercial application of these techniques impossible.  Although fiber lasers are commercially avilabile at multi-kW powers, ultrafast fiber lasers are currently limited to below 100W due to nonlinear effects that destroy the spectrum and compressibility of the pulses.

To scale the power of ultrafast fiber lasers, we are redefining ultrafast fiber lasers from the ground up, including exotic fiber designs, nonlinear propagation solutions, ultra-high-brightness pumping, techniques for mitigating the fundamental self-focusing limit, and novel packaging to mitigate unwanted thermo- and stress-optical effects.


High Brightness Semiconductor Lasers

Broad-area laser (BAL) diodes are useful for pumping high-power fiber lasers and amplifiers. However, they suffer greatly due to free-carrier induced self-focusing that leads to beam filamentation and reduced beam quality.

We are exploring methods of on-chip, integrated, continuous filtering in order to suppress filamentation in broad-area lasers in order to relieve the pumping limitations on high-power fiber lasers/amplifiers that BALs impose.  We are using a custom Beam Propagation Method code to design gain, current, and index structures that preferentially and continuously filter the high spatial frequency light characteristics of filamentation before it experiences large amounts of gain.


© John Marciante 2018