A 2 μm wavelength, 90 mJ, 5 Hz pulsed Ho laser is described with wavelength control to precisely tune and lock the wavelength at a desired offset up to 29 GHz from the center of a CO2 absorption line Once detuned from the line center the laser wavelength is actively locked to keep the wavelength within 19 MHz standard deviation about the setpoint This wavelength control allows optimization of the optical depth for a differential absorption lidar (DIAL) measuring atmospheric CO2 concentrations The laser transmitter has been coupled with a coherent heterodyne receiver for measurements of CO2 concentration using aerosol backscatter; wind and aerosols are also measured with the same lidar and provide useful additional information on atmospheric structure Range-resolved CO2 measurements were made with <24% standard deviation using 500 m range bins and 67 min⁡ (1000 pulse pairs) integration time Measurement of a horizontal column showed a precision of the CO2 concentration to <07% standard deviation using a 30 min⁡ (4500 pulse pairs) integration time, and comparison with a collocated in situ sensor showed the DIAL to measure the same trend of a diurnal variation and to detect shorter time scale CO2 perturbations For vertical column measurements the lidar was setup at the WLEF tall tower site in Wisconsin to provide meteorological profiles and to compare the DIAL measurements with the in situ sensors distributed on the tower up to 396 m height Assuming the DIAL column measurement extending from 153 m altitude to 1353 m altitude should agree with the tower in situ sensor at 396 m altitude, there was a 79 ppm rms difference between the DIAL and the in situ sensor using a 30 min⁡ rolling average on the DIAL measurement

Side-line tunable laser transmitter for differential absorption lidar measurements of CO2: design and application to atmospheric measurements.

Rare-earth-doped fiber lasers are promising contenders in the development of spectroscopy, free-space communications, and countermeasure applications in the 3–5 μm spectral region. However, given the limited transparency of the commonly used fluorozirconate glass fiber, these systems have only achieved wavelength coverage up to 3.8 μm, hence fueling the development of more suitable fiber glass compositions. To this extent, we propose in this Letter a novel heavily holmium-doped fluoroindate fiber, providing extended transparency up to 5 μm, to demonstrate the longest wavelength room-temperature fiber laser at 3.92 μm. Achieving ∼200  mW of output power when cladding pumped by a commercial 888 nm laser diode, this demonstration paves the way for powerful mid-infrared fiber lasers emitting at and beyond 4 μm.

Room-temperature fiber laser at 3.92 μm

Hybrid fiber-laser-pumped solid-state lasers exploit high-power cladding-pumped fiber lasers for direct (in-band) pumping of a crystal-based solid-state laser to reduce heating in the laser crystal, and hence allow scaling to higher power in both continuous-wave (CW) and pulsed modes of operation. In this paper, we briefly review the attractions of the hybrid laser approach for generation of output in the ~ 1.6 mum wavelength regime and consider the main design considerations for efficient operation of hybrid lasers based on Er:YAG in both CW and pulsed modes of operation. Examples of hybrid Er:YAG lasers, pumped by Er,Yb codoped fiber lasers at 1532 nm, with CW output powers up to 60 W at 1645 nm and 31 W at 1617 nm and slope efficiencies of 80% and 47% with respect to incident pump power, respectively, are described. In Q-switched mode of operation, pulse energies up to 30.5 mJ were obtained, limited by coating damage. Finally, the prospects for further increase in output power and improvement in overall performance in CW and Q-switched modes of operation will be discussed.

Fiber-Laser-Pumped Er:YAG Lasers

A mid-infrared supercontinuum extending up to 5.4 μm is generated in a low-loss fluoroindate fiber. It is pumped with an erbium-doped fluoride fiber amplifier seeded with 400 ps pulses at 2.75 μm. Both fibers are fusion spliced to increase the robustness and long-term stability of the system. With more than 82% of the total power beyond 3 μm, this approach is promising for efficient mid-IR light generation.

Mid-IR supercontinuum from 2.4 to 5.4 μm in a low-loss fluoroindate fiber.

The mid-infrared (MIR) represents a large portion of the electromagnetic spectrum that is progressively being exploited for an enormous number of applications. Thermal imaging cameras, dental and skin resurfacing lasers, and narcotics detectors at airports are all mainstream examples involving the MIR, but potential applications of MIR technologies are much larger. Accessing the unique opportunities afforded by the MIR is critically dependent on the specific characteristics of MIR emitting sources that become available. In this review, we survey an important enabling technology to the opening up of MIR science and applications, namely that driven by fiber-based sources of coherent MIR radiation. In this review paper, we describe many of the key advances in the innovation and development of such sources over the past few decades and discuss many of the underlying science and technology issues that have resulted in specific recent source achievements, especially in light of new applications enabled by these new source capabilities. We also discuss a few specific anticipated future needs and some potentially disruptive approaches to future MIR fiber source development.

Fiber-based sources of coherent MIR radiation: key advances and future prospects (invited).

Mid infrared lasers for remote sensing applications

High repetition rate operation of an injection seeded Ho:YLF laser has been demonstrated. For 1 kHz operation, the output pulse energy reaches 5.8mJ and the optical-to-optical efficiency is 39% when the pump power is 14.5W.

https://ntrs.nasa.gov/api/citations/20090009805/downloads/20090009805.pdf

High Repetition Rate and Frequency Stabilized Ho:YLF Laser for CO2 Differential Absorption Lidar

A highly efficient Q-switched Ho:YLF laser pumped by a Tm:fiber laser has been designed and demonstrated. When the pump power is 30 W, the pulse energy is 30 mJ at the repetition rate of 100 Hz.

/pdf/highly-efficient-q-switched-ho-ylf-laser-pumped-by-tm-fiber-4gg0rakygv.pdf

Highly efficient Q-switched Ho:YLF laser pumped by Tm:fiber laser

An injection-seeded, Q-switched Ho:YLF laser has been developed. For 13W pumping from a CW Tm:fiber laser, the energy and width of single longitudinal mode pulse are 5.5mJ and 50ns, respectively. The repetition rate is 1.25kHz.

Single longitudinal mode, high repetition rate, Q-switched Ho:YLF laser for remote sensing

A conductively-cooled Ho:Tm:LuLiF laser oscillator generates 1.6J normal mode pulses at 10Hz with optical to optical efficiency of 20%. When the laser head module is used as the amplifier, the double-pass small-signal amplification excesses 25.

/pdf/efficient-operation-of-conductively-cooled-ho-tm-lulif-laser-3iiswz4r8r.pdf

Hyung Lee

Papers

Mid infrared lasers for remote sensing applications

High Repetition Rate and Frequency Stabilized Ho:YLF Laser for CO2 Differential Absorption Lidar

Highly efficient Q-switched Ho:YLF laser pumped by Tm:fiber laser

Single longitudinal mode, high repetition rate, Q-switched Ho:YLF laser for remote sensing

Efficient Operation of Conductively Cooled Ho:Tm:LuLiF Laser Oscillator/Amplifier