Pulsed Tm-fiber Laser For Mid-ir Generation

The thulium fiber laser has gained interest due to its long emission wavelength, large bandwidth (~1.8 – 2.1 µm), high efficiencies (~60 %), and high output power levels both in cw as well as pulsed regimes. Applications like remote sensing, machining, medical tissue ablation, and mid-infrared generation benefit from high peak power thulium laser sources. Pulsed thulium fiber laser systems are advancing rapidly towards higher peak power levels and are becoming the preferred sources for these applications. This dissertation work describes the development of novel nanosecond pulsed thulium fiber laser systems with record high peak power levels targeting mid-infrared generation. The peak power scaling in thulium fiber lasers requires new fiber designs with larger mode field area (MFA) than commercially available step index large mode area (SI-LMA) fibers. Two different prototypes of thulium doped photonic crystal fibers (PCF) were investigated for high peak power generation. The first prototype is a flexible-PCF with MFA twice as large as SILMA fiber and the second prototype is a PCF-rod with six times larger MFA. A robust single stage master oscillator power amplifier (MOPA) source based on flexible-PCF was developed. This source provided narrow linewidth, tunable wavelength, variable pulse duration, high peak power, and high energy nanosecond pulses. The PCF-rod was implemented as a second stage power amplifier. This system generated a record level of ~1 MW peak power output with 6.4 ns pulse-duration at 1 kHz repetition rate. This thulium doped PCF based MOPA system is a state of the art laser source providing high quality nanosecond pulses. iv The single stage MOPA system was successfully implemented to pump a zinc germanium phosphide (ZGP) crystal in an optical parametric oscillator (OPO) cavity to generate 3 - 5 µm wavelengths. The MOPA source was also used to demonstrate backside machining in silicon wafer. The PCF based laser system demonstrated an order of magnitude increase in the peak power achievable in nanosecond thulium doped fiber laser systems, and further scaling appears possible. The increase in peak power will enable additional capabilities for mid-infrared generation and associated applications

Comparison of higher-order mode suppression and Q-switched laser performance in thulium-doped large mode area and photonic crystal fibers

We report the influence of higher order modes (HOMs) in large mode fibers operation in Q-switched oscillator configurations at similar to 2 mu m wavelength. S-2 measurements confirm guiding of LP11 and LP02 fiber modes in a large mode area (LMA) step-index fiber, whereas a prototype photonic crystal fiber (PCF) provides nearly single-mode performance with a small portion of light in the LP11 mode. The difference in HOM content leads to a significant difference in Q-switched oscillator performance. In the step-index fiber, the percentage of cladding light increases by 20% to \u3e 40% with increasing pulse energy to similar to 250 mu J. We accredit this degradation to saturation of the gain in the fundamental mode leading to more light generated in the HOMs, which is eventually converted into cladding light. No such degradation is seen in PCF laser system for \u3e 400 mu J energies

Welding Of Polymers Using A 2 Μm Thulium Fiber Laser

Absorber-free transmission and butt-welding of different polymers were performed using thulium fiber laser radiation at the wavelength 2 μm. The relations between the laser process conditions and the dimensions and quality of the seam were investigated by means of optical and phase-contrast microscopy. Mechanical properties of the weld joints were studied in tensile strength tests. Laser-welded polyethylene samples revealed a tensile strength of greater than 80% of the bulk material strength. Transmission welding of different polymer combinations featured the formation of different joint classes depending on the spectral properties. The experiments demonstrate new application areas of mid-IR fiber laser sources for materials processing. © 2012 Elsevier Ltd

Generation And Amplification Of Femtosecond Pulses In Tm: Fiber

We describe the generation and amplification of femtosecond pulses at 2-μm wavelength in thulium doped fiber. The mode-locked oscillator is a ring cavity based on single-mode Tm:fiber producing stable soliton pulses at 70 MHz repetition rate with 40 pJ pulse energy, centered at ∼1.97 μm wavelength with ∼8 nm (FWHM) spectral width. These pulses seed a Tm:fiber based Raman amplifier, which increases the energy up to 9 nJ. The spectrum is broadened up to 40 nm (FWHM) and the center wavelength can be shifted from ∼1.97 - 2.15 μm. The Raman solitons are inherently time-bandwidth limited with pulse durations \u3c150 fs. © 2011 SPIE

182 Nj All Thulium Fiber Cpa System

150 fs pulses spectrally centered at 2020 nm were generated in a Raman amplifier. Pulses were temporal stretched and amplified to 182 nJ with a spectral width of 60 nm. ©2011 Optical Society of America

182 Nj All Thulium Fiber Cpa System

150 fs pulses spectrally centered at 2020 nm were generated in a Raman amplifier. Pulses were temporal stretched and amplified to 182 nJ with a spectral width of 60 nm. ©2011 Optical Society of America

Generation and amplification of 350 fs, 2 μm pulses in Tm:fiber

Amplified ultrashort pulses at 2 μm are of great interest for atmospheric sensing, medical, and materials processing applications. We describe the generation and amplification of femtosecond 2 μm pulses in thulium doped silica fiber. Mode-locked eye-safe laser pulses at ∼2 μm were generated in a Tm:fiber oscillator using a single-walled carbon nanotube saturable absorber. Stable mode-locking was achieved at a repetition rate of 70 MHz with soliton pulses reaching energies of ∼40 pJ with a spectral bandwidth of ∼8 nm. Autocorrelation measurements indicated bandwidth limited pulses of ∼500 fs duration. This oscillator was used to seed a Tm:fiber amplifier in both free space and fiber coupled configurations. Effects of dispersion compensation and pulse amplification are reported. © 2011 SPIE

Generation And Amplification Of 350 Fs, 2 Μm Pulses In Tm:Fiber

Amplified ultrashort pulses at 2 μm are of great interest for atmospheric sensing, medical, and materials processing applications. We describe the generation and amplification of femtosecond 2 μm pulses in thulium doped silica fiber. Mode-locked eye-safe laser pulses at ∼2 μm were generated in a Tm:fiber oscillator using a single-walled carbon nanotube saturable absorber. Stable mode-locking was achieved at a repetition rate of 70 MHz with soliton pulses reaching energies of ∼40 pJ with a spectral bandwidth of ∼8 nm. Autocorrelation measurements indicated bandwidth limited pulses of ∼500 fs duration. This oscillator was used to seed a Tm:fiber amplifier in both free space and fiber coupled configurations. Effects of dispersion compensation and pulse amplification are reported. © 2011 SPIE

A High Peak Power, Nanosecond Tm:Fiber Mopa System For Mid-Ir Opo Pumping

We report on a thulium fiber MOPA system utilizing a photonic crystal fiber (PCF) based power amplifier generating \u3e40 kW, ∼6.5 ns pulses as a tunable, narrow linewidth source for mid-IR OPO pumping. © 2013 The Optical Society

Chirped Pulse Amplification In Tm Doped Fiber Using A Chirped Bragg Grating

Femtosecond pulses were generated and amplified via chirped pulse amplification in Tm:fiber. The mode-locked oscillator centered at 1975 nm produced 800 fs transform limited pulses with 40 pJ energy at 60 MHz repetition rate. Subsequently, a soliton self-frequency shift in a thulium-doped fiber pumped with a 793 nm diode was used to amplify pulses to 3 nJ, shift the center wavelength, and reduce the pulse duration to 150 fs. This pulse was tuned to 2020 nm to match the center wavelength of a chirped Bragg grating. The pulses were stretched to \u3e160 ps pulses, amplified to 85 nJ in single-mode Tm:fiber and recompressed to 400 fs. © 2013 Copyright SPIE