Tm:fiber laser in-band pumping a cryogenically-cooled Ho:YAG laser

Abstract

Abstract:Cryogenically-cooled diode-pumped lasers have received significant interest in recent years for their demonstrated orders of magnitude improvement in output radiance using simple laser resonator configurations, with respect to their room temperature counterparts. Here we present a technique that offers the potential for a further order of magnitude radiance improvement utilising the in-band pumping hybrid-laser architecture, which employs high-power fiber lasers to excite cryogenically-cooled bulk gain media. The ability to exploit the quasi-four-level nature of a two-level laser system at very cold temperatures enables the operation of very low quantum defect transitions, thus providing a tenfold reduction in the required thermal dissipation per unit power for the in-band pumped Ho:YAG laser discussed here, as compared to diode-pumped Yb:YAG. Preliminary results will be discussed, for a narrow linewidth Tm:fiber laser system operating in the 100W regime, pumping a cryogenically cooled Ho:YAG gain element, and employing a simple cavity configuration. Low quantum defect operation and power-scaling potential will be discussed. word abstractCryogenically-cooled diode-pumped lasers have received significant interest in recent years for their demonstrated orders of magnitude improvement in output radiance using simple laser resonator configurations. Here we present a technique that offers the potential for a further order of magnitude improvement utilising the in-band-pumping hybrid-laser architecture to excite cryogenically-cooled bulk gain media. Preliminary results will be discussed, for a narrow linewidth Tm:fiber MOPA system operating in the 100W regime, pumping a cryogenically cooled Ho:YAG gain element, and employing a simple cavity configuration. Low quantum defect operation and power-scaling potential will be discussed.

Ho:YAG absorption cross sections from 1700 to 2200 nm at 83, 175, and 295 K

“…In disagreement with the absorption cross-section data shown in Fig. 1(b) of [12], and the data of [13] upon which it is based, which show the peak absorption cross section at 1908 nm at 300 K, our data show that the highest absorption amplitude is obtained at 175 K, followed by 83 and 295 K. Thus the absorption cross section at 295 K is less than that obtained at 83 K. At 1933 nm, the absorption cross section is highest at 175 K as well, followed by 83 and 295 K, so absorption at that wavelength is greater at 83 K than at 295 K as well.…”

“…Cryogenically cooled Ho:YAG (YAG, yttrium aluminum garnet) lasers using liquid nitrogen as the coolant are in their infancy, and may be developed to provide a high efficiency, high-averagepower (HAP) near-infrared source with excellent beam quality operating near 2100 nm. A recent paper has demonstrated the potential of this system [12]. A Tm:Glass fiber laser pump with tunability from 1920 to 2110 nm and a CW output power up to about 57 W was used to pump the 1932 nm absorption peak of the 5 I 8 -5 I 7 absorption transitions, resulting in a small quantum defect (∼7.9%) and output at 2097 nm.…”

The Application of Cryogenic Laser Physics to the Development of High Average Power Ultra-Short Pulse Lasers

“…Other cryogenic CW lasers have been developed recently as well. In [140], the authors describe a cryogenically-cooled CW Ho:YAG laser pumped by a Tm:Glass fiber laser with output at 1932 nm, producing 8 W of CW power output at ~2100 nm. In addition, still pumping at 1932 nm, the authors report 2.5 W of CW output power at 1976 nm, resulting in a very low quantum defect of 2.2%.…”

Efficient, low threshold, cryogenic Ho:YAG laser

“…As a result the corresponding absorption spectrum of the 5 I 8 manifold is broad and consists of many features [22,23]. Mackenzie et al [10] reported a LN cooled Ho:YAG laser pumped by a thulium-doped fibre laser (TDFL) at 1932 nm that produced about 8 W of output power with a slope efficiency of 28%. The authors also described substantial narrowing of the pump absorption in the Ho:YAG as they reached CTs.…”

“…It has previously been demonstrated that cryogenic cooling of the laser gain medium can address the problems associated with the 3-level nature of Ho:YAG [10,11]. Cooling the gain medium to cryogenic temperatures (CTs), redistributes the thermal population of the ground state manifold, resulting in 4-level laser behavior.…”