Mid-infrared (mid-IR) fiber lasers that are based on dysprosium (Dy) as the active laser ion provide emission in the wavelength range between 2.6–3.4 μm and can thus bridge the spectral gap between holmium (Ho) and erbium (Er) based mid-IR lasers. Another distinct feature is the wide choice of pump wavelengths (1.1 μm, 1.3 μm, 1.7 μm, and 2.8 μm) that can be used. To date, pump wavelengths shorter than 1.1 μm have not been reported and all demonstrated pump wavelengths apart from in-band pumping suffer from pump excited state absorption (ESA). In this paper, we report new excitation wavelengths, 0.8 μm and 0.9 μm, for Dy-doped mid-IR fiber lasers. We have measured 18.5% and 23.7% slope efficiency (relative to launched pump power) for 0.8 μm and 0.9 μm pumping wavelengths, respectively. By comparing the residual pump power of experimental and numerical simulation data of a 0.5 m Dy-doped fiber, we have found that these new excitation wavelengths are free from pump ESA. Moreover, the high power laser diodes are commercially available at these new excitation wavelengths; therefore, the realization of a diode-pumped Dy-doped mid-infrared fiber laser might become feasible in the near future.
We present preliminary results relating to laser emission at 3:16 µm from a Dy fiber laser that is diode pumped at 800 nm. To allow strong diode pump absorption and to capture improved quantum efficiencies resulting from cross relaxation, the Dy:ZBLAN fiber was co-doped with Tm ions in a 10 to 1 concentration ratio to Dy. A resonant energy transfer from Tm to Dy provides an inversion on the 6H13/2 to 6H15/2 transition. Maximum output power of 5.5 mW at a slope efficiency of 1.3 % was produced from a highly non-optimal arrangement. System performance is bench marked against well established resonant pumping of the Dy upper state. Measurement of fluorescence lifetimes of both dopants allows for qualitative assessment of the energy transfer efficiency. A potentially detrimental energy transfer mechanism is identified and discussed.
In this paper, we report the first (to the best of our knowledge) GaN laser diode, emitting at 445 nm, pumped dysprosium (Dy) doped ZBLAN fiber laser for yellow emission using a simple setup. In our yellow laser experiment, we have used a commercially available Dy-doped ZBLAN fiber, which is originally designed for mid-infrared lasers demonstration and not optimized for visible laser design, as a laser active medium. For yellow (∼576 nm) lasing, we have exploited the 4F9/2 to 6H13/2 laser transition of a Dy ion, which is a quasi four level system. The performance of the yellow laser system is investigated by using two different Dy-doped fiber lengths (0.6 m and 5.95 m). The measured lasing thresholds are 7 mW and 28 mW for 0.6 m and 5.95 m of Dy-doped fiber, respectively. However, the maximum laser slope efficiency with respect to absorbed pump power is only 2.3% for 0.6 m of Dy-doped fiber. The laser slope efficiency decreases to 0.9% and the threshold increases to 28 mW for 5.95 m of Dy-doped fiber, which are result of fiber background loss at the signal wavelength. In addition, we have observed the pump excited state absorption at 445 nm pumping wavelength and estimated the pump ESA cross-section via numerical simulation.
The yellow spectral region has applications in medicine, ophthalmology, acne treatment, and ytterbium based optical clock, which is recommended as the secondary representation of System International (SI) second. Lasing in this spectral region can be achieved by using sum frequency and second harmonic generation, which are complex methods. Here, we have reported the first (to the best of our knowledge) GaN laser diode pumped dysprosium (Dy) doped ZBLAN fibre laser for yellow lasing using a simple setup. Due to the four-level system, the laser oscillation threshold is low and about 7.0 mW for 0.6 m of Dy-doped ZBLAN fibre. However, the maximum slope efficiency is only 2.3% with the available 2% output coupler. In our investigation, we have identified two possible factors, fibre background loss and pump excited state absorption, for such a low slope efficiency.
The performance of mid-infrared fiber lasers operating on the 3.5 μm transition in erbium has improved significantly since the first demonstration that dual wavelength pumping allowed efficient operation. In this contribution, we will discuss the progress of fiber lasers that operate on this transition with an emphasis on advances towards short pulse generation and wavelength agility. Mode-locked operation using saturable absorption is a robust means of achieving ultra-short pulse operation in the near infrared but achieving this in the mid-infrared has been elusive. We will also describe our characterization of the mid-infrared performance of graphene, a material which has been very successfully applied to mode-locked pulse generation in the near infrared.
Mode-locked fiber lasers are currently limited to sub-3-μm wavelengths, despite application-driven demand for longer wavelength mid-IR pulse sources. Erbium- and holmium-doped fluoride fiber lasers are emerging for 2.7-2.9 μm emission, yet further extending this coverage is challenging. Here, we propose a new approach using dysprosium-doped fiber with frequency shifted feedback (FSF), achieving 33 ps pulses with up to 2.7 nJ energy, tunable from 2.97 to 3.30 μm. Notably, this is the longest wavelength mode-locked fiber laser and the most broadly tunable pulsed fiber source to date. Simulations are also performed, offering insights into the dynamics of FSF pulse generation.
The development of new, compact mid-infrared light sources is critical to enable biomedical sensing applications in resource-limited environments. Here, we review progress in fiber-based mid-IR sources, which are ideally suited for clinical environments due to their compact size and waveguide format. We first discuss recent developments in mid-IR supercontinuum sources, which exploit nonlinear optic phenomena in highly nonlinear materials (pumped by ultrashort pulse lasers) to generate broadband spectra. An emerging alternative approach is then presented, based on broadly tunable mid-IR fiber lasers, using the promising dysprosium ion to achieve orders of magnitude higher spectral power density than typical supercontinua. By employing an acousto-optic tunable filter for wavelength tuning, an electronically controlled swept-wavelength mid-IR fiber laser is developed, which is applied for absorption spectroscopy of ammonia (NH3), an important biomarker, with 0.3 nm resolution and 40 ms acquisition time.
Previously reported progress in 3 micron dysprosium doped ZBLAN fiber lasers achieved record conversion efficiency but was limited in tuneability due to the inband nature of the pumping scheme. Near infrared pumping has also been demonstrated but was limited in conversion efficiency due both to pump excited state absorption and large quantum defect. We address these limitations by employing a Raman fiber laser operating at 1700 nm as a pump source. Reduced quantum defect shows promise for efficiency gains while maintaining near infrared pumping and the increased gain bandwidth shows promise for pulsed operation.
Recent progress in our work on the development of three micron class dysprosium-doped ZBLAN fiber lasers will be presented. Of particular note is the achievement of 51% slope efficiency which to our knowledge represents a record for all 3 micron class fiber lasers. This result is obtained for an in-band pumping scheme which also allowed for demonstration of continuous tuning over a range of 400nm with an extreme emission wavelength of 3.35 microns.
Spatial and temporal fluctuations of the electric polarization were imaged in polymer thin films near the glass
transition using electric force microscopy. Below the glass transition the fluctuations are quasi-static and spatial
fluctuations were found to quantitatively agree with predictions for thermal fluctuations. Temporal fluctuations appear
near the glass transition. Images of the space-time nanoscale dynamics near the glass transition are produced and
analyzed. Local, complex dielectric susceptibility was also studied, and shows that dynamics on the free-surface are
faster relative to the bulk.