Ho:YLF
Ho:YLF is a very attractive laser material, because the lifetime of the upper laser level is much longer ( ~ 14 ms) than in Ho:YAG and the emission cross sections are higher. Additionally the thermal lens in Ho:YLF is much weaker, which helps to generate diffraction limited beams even under intense end-pumping.
The primary advantage of directly pumping the Ho 5I7 is that it does not have to depend on energy transfer, which lends itself to various radiative and non-radiative losses. Up-conversion losses that have deleterious effect in high-energy Q-switched lasers are eliminated. In the near future experiments with different Ho:YLF crystals are planned to reduce the laser threshold and increase the maximum output power.
Parameter
| Orientation | a-cut |
| Clear aperture | >90% |
| Face dimensions tolerance | +0/-0,1 mm |
| Length tolerance | ±0,1 mm |
| Parallelism error | <10 arcsec |
| Perpendicularity error | <10 arcmin |
| Protective chamfers | <0,1 mm at 45˚ |
| Surface quality | 10-5 S-D |
| Surface flatness | <λ/10@632,8 nm |
| Coatings | R<0,35%@1900-2100 nm on both faces |
| LIDT | >10 J/cm2@2060 nm, 10 ns |
| Mount | Unmounted |
| Crystal structure | tetragonal |
| Density | 3.95 g/cm3 |
| Mohs hardness | 5 |
| Thermal conductivity | 6 Wm-1K-1 |
| dn/dT | -4.6×10-6 (||c) K-1, -6.6×10-6 (||a) K-1 |
| Thermal expansion coefficient | 10.1×10-6 (||c) K-1, 14.3×10-6 ((||a) K-1 |
| Typical doping level | 0.5-1% |
| Absorption peak wavelength | 1940 nm |
| Absorption cross-section at peak | 1.2×10-20 cm2 |
| Absorption bandwidth at peak wavelength | ~18 nm |
| Laser wavelength | 2060 nm |
| Lifetime of 5I7 energy level | 10 ms |
| Emission cross-section | 1.8×10-20 cm2 |
| Refractive index @1064 nm | no=1.448, ne=1.470 |
Feature
- Long upper laser level lifetime ~ 15 ms
- Higher emission cross-section
- Naturally birefringent material
- Low dn/dT –> weak thermal lensing
- Highest (to the best of our knowledge) CW output of 21 W for 2-μm Ho:YLF laser
- Efficient Q-switched operation (up to 37 mJ per pulse)
Application
- Remote sensing
- Pollutant Control
- Military defense
Literature
| [1] Jacek, Kwiatkowski, Jan, et al. An efficient continuous-wave and Q-switched single-pass two-stage Ho:YLF MOPA system[J]. Optics & Laser Technology, 2015. |
| [2] Bourdet G L , Lescroart G , Muller R . Spectral characteristics of 2 μm microchip Tm:YVO 4 and Tm,Ho:YLF lasers[J]. Optics Communications, 1998, 150(1-6):141-146. |
| [3] Nagasawa C , Sakaizawa D , Hara H , et al. Lasing characteristics of a CW Tm,Ho:YLF double cavity microchip laser[J]. Optics Communications, 2004, 234(1-6):301-304. |
| [4] Zhang X , Bao X , Li L , et al. Laser diode end-pumped passively Q-switched Tm,Ho:YLF laser with Cr:ZnS as a saturable absorber[J]. Optics Communications, 2012, 285(8):2122–2127. |
| [5] Wang R , Huang X , Wang Y , et al. Intense 3.9 μm emission of Ho3+ doped YAlO3 single crystal[J]. Infrared Physics & Technology, 2018:S1350449517307545. |
| [6] Vieira N D , Ranieri I M , Tarelho L , et al. Laser development of rare-earth doped crystals[J]. Journal of Alloys and Compounds, 2002, 344(1-2):231-239. |
| [7] Yang X T , Mu Y L , Zhao N B . Ho:SSO solid-state saturable-absorber Q switch for pulsed Ho:YAG laser resonantly pumped by a Tm:YLF laser[J]. Optics & Laser Technology, 2018, 107:398-401. |
| [8] Elder I F , Payne M . Lasing in diode-pumped Tm:YAP, Tm,Ho:YAP and Tm,Ho:YLF[J]. Optics Communications, 1998, 145(1-6):329-339. |
| [9] Dai T Y , Fan Z G , Wu J , et al. High power single-longitudinal-mode Ho:YLF unidirectional ring laser based on a composite structure of acousto-optic device and wave plate[J]. Infrared Physics & Technology, 2017, 82:40-43. |
| [10] Sato H , Bensalah A , Machida H , et al. Growth and Characterization of 3-in Size Tm, Ho-Codoped LiYF4 and LiLuF4 Single Crystals by the Czochralski Method[J]. Journal of Crystal Growth, 2003, 253(s 1–4):221–229. |
| [11] F Chiossi, Borghesani A F , Carugno G . Infrared and visible scintillation of Ho 3+ -doped YAG and YLF crystals[J]. Journal of Luminescence, 2018, 203:203-207. |
| [12] Zhang X , Wang Y , Ju Y . LD-pumped actively Q-switched Tm,Ho:YLF laser at room temperature[J]. Optics & Laser Technology, 2007, 39(1):78-81. |
| [13] Bourdet G L . Gain and absorption saturation coupling in end pumped Tm:YVO 4 and Tm,Ho:YLF CW amplifiers[J]. Optics Communications, 2000, 173(1-6):333-340. |
| [14] Bachmann L , Craievich A F , Zezell D M . Crystalline structure of dental enamel after Ho:YLF laser irradiation[J]. Archives of Oral Biology, 2004, 49(11):923-929. |
| [15] Zhang C , Zu Y , Yang W , et al. Epsilon-near-zero medium for optical switches in Ho solid-state laser at 2.06μm[J]. Optics & Laser Technology, 129. |
| [16] Yang X T , Song E Z , Xie W Q . Compact resonantly intra-cavity pumped tunable Ho:Sc2SiO5 laser[J]. Infrared Physics & Technology, 2017, 85:154-156. |
| [17] Zhang X , Liang Y , Li L , et al. Bistable performances of diode-end-pumped quasi-three-level Tm,Ho:YLF lasers[J]. Optics Communications, 2010, 283(6):1086-1089. |
| [18] Yang C , Ju Y , Yao B , et al. Passively Q-switched Ho:YLF laser pumped by Tm3+-doped fiber laser[J]. Optics & Laser Technology, 2016. |
| [19] Wang J , Yuan L , Zhang Y , et al. Generation of 320 mW at 10.20 μm based on CdSe Long-wave Infrared Crystal[J]. Journal of Crystal Growth, 2018:S0022024818301118. |
| [20] Zhang C , Zhang F , Fan X , et al. Passively Q-switched operation of in-band pumped Ho:YLF based on Ti3C2Tx MXene[J]. Infrared Physics & Technology, 2019, 103:103076. |
| [21] Zhang X , Ju Y , Wang Y . Diode-pumped single frequency Tm,Ho:YLF laser at room temperature[J]. Chinese Optics Letters, 2005, 3(8). |
| [22] Jing W , Wang Y , Dai T , et al. Single-longitudinal-mode generation in a Ho: YLF ring laser with double corner cubes resonator[J]. Infrared Physics & Technology, 2018, 92:367-371. |
| [23] Theoretical and experimental study of a single frequency Tm,Ho:YLF laser[J]. Optics & Laser Technology, 2007, 39(4):782-785. |
| [24] Tonelli M , Falconieri M , Lanzi A , et al. Comparison of Tm-sensitized Ho:Yag and Ho:YLF crystals for a laser-pumped 2 μm CW oscillator[J]. Optics Communications, 1996, 129(1-2):62-68. |
| [25] Kwiatkowski J , Zendzian W , J Abc Zynski J K , et al. Continuous-wave and high repetition rate Q-switched operation of Ho:YLF laser in-band pumped by a linearly polarized Tm:fiber laser[J]. Optics & Laser Technology, 2014, 63:66-69. |
| [26] Dai, T, Y, et al. A tunable and single-longitudinal-mode Ho:YLF laser[J]. Infrared Physics & Technology, 2016. |
| [27] Izawa J , Nakajima H , Hara H , et al. A tunable and longitudinal mode oscillation of a Tm,Ho:YLF microchip laser using an external etalon[J]. Optics Communications, 2000, 180(1-3):137-140. |
| [28] Nagasawa C , Suzuki T , Nakajima H , et al. Characteristics of single longitudinal mode oscillation of the 2 μm Tm,Ho:YLF microchip laser[J]. Optics Communications, 2001, 200(1-6):315-319. |
| [29] Burger A , Ndap J O , Chattopadhyay K , et al. CHAPTER 4. Bulk Semiconductors for Infrared Applications[J]. Photodetectors and Fiber Optics, 2001. |
| [30] Concentration effects on the IR-luminescent channels for Er- and Ho-doped LiYF 4 crystals |
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