Yi Wu

Abstract

Researchers at the University of Central Florida have invented an ultrafast Holmium laser system that can generate multi-millijoule-level laser pulse energy centered at 2.05 µm and a 1 kHz repetition rate. With such capabilities, the laser can produce long, ultra-broad bandwidth (4-12 µm wavelength), mid-IR laser pulses to enable high harmonic generation (HHG) for creating attosecond laser pulses. The pulses are useful for resolving and controlling events in the atto- femto- or pico-second timescales, such as nuclear fusion, biomolecule manipulation, biological imaging or electronic information storage.

Key to the invention is its ability to reduce the required gain by seeding the laser system with microjoule-level energy pulses. For example, after propagating in a dual-stage Ho:YLF crystal in just four passes, the seed pulse is amplified up to a pulse energy of 6 mJ. Thus, the system not only reduces the overall complexities associated with conventional technologies, but it also reduces the amount of gain narrowing. The UCF system is more cost-effective and efficient, as well, since it is water-cooled (versus cryogenically cooled) and incorporates the use of commercially-available lasers.

Technical Details

As an example setup of the UCF Holmium laser system invention, the seed laser may be a Ti:Sapphire and the amplifier may be a chirped-pulse amplifier consisting of a stretcher, an amplification stage, and a compressor. Within the amplification stage is a Holmium gain medium (such as a Ho:YLF crystal with an emission peak centered at 2.05 µm and an absorption peak at 1.94 µm). The stretcher and compressor may include any dispersive optics like diffraction gratings or prisms. For a smaller system footprint, the stretcher and compressor can be a single optical component, such as one formed from chirped volume Bragg gratings (CVBGs) to reflect chirped seed pulses onto the optical component after amplification.

Benefit

Market Application

Abstract

UCF researchers have developed an innovative method that reduces and/or eliminates gain clamping in a solid-state laser and amplifier systems and works with other index-matching methods. The design works well with standard cladding/coating materials that employ either tunable index of refraction or tunable absorption materials and with materials that have no existing index-matching procedures available. This technique can also be used as part of an amplifier offering the benefits of both cryogenic cooling and anti-transverse lasing.

Technical Details

This novel system provides a solid-state laser/amplifier gain medium that prevents parasitic lasing and is compatible with operation in evacuated and cryogenic environments. The gain medium is comprised of a perimetrical edge with an ASE-absorbing epoxy composition, with an index refraction that matches the gain medium's index of refraction, applied on a portion of the edge. By bonding a light-absorbing, refractive index-matched material to the edges of the laser gain medium, the ASE in the transverse direction can be coupled out to prevent the build-up of parasitic oscillation. This technique reduces the strength of the Fresnel reflections and adds high absorption losses, both of which increase the losses in the transverse direction. Different epoxies with high and low refractive indexes are combined in predetermined amounts to create an optical refractive index that closely matches the laser gain medium. To enhance the absorption power, superfine metal particles with absorption at ASE wavelengths may be added to the epoxy base.

Benefit

Market Application