Acta Photonica Sinica, Volume. 49, Issue 11, 77(2020)
Research Progresses of Alexandrite Solid-state Lasers （Invited）
Figures & Tables(35)
![c-axis view of alexandrite structure[21] and the image of alexandrite crystals grown by the Czochralski method in Crystech Co., Ltd.](/Images/icon/loading.gif){kind=icon}
Fig. 1.
Fig. 2. Simplified energy level diagram for the alexandrite crystal[22]
Fig. 3. Alexandrite absorption spectrum for Cr3+ dopant concentration of 0.063 at.% and alexandrite fluorescence rate spectra at 300 K[23]
Fig. 4. Schematic diagram of the single bounce alexandrite slab laser, the double-bounce alexandrite slab laser and the extended double bounce alexandrite slab laser[12]
Fig. 5. Schematic diagram of diode-pumped alexandrite vortex laser[44]
Fig. 6. Pumping configuration with two diode modules and the resonator configuration of the alexandrite laser[14]
Fig. 7. Experimental arrangements for fiber-delivered polarized diode single-end-pumped alexandrite laser and double-pass-end-pumped alexandrite laser[45]
Fig. 8. Effective emission cross section spectra of alexandrite for E∥
Fig. 9. Thermal lens dioptric power and laser power as a function of the absorbed pump power[48]
Fig. 10. Schematic of double-end-pumped L-shaped alexandrite laser[13]
Fig. 11. Schematic layout of the blue LD pumped alexandrite laser system at cryogenic temperatures and within the temperature range of 300~400 K[49]
Fig. 12. Schematic layout of alexandrite laser system for Q-switching[9]
Fig. 13. Schematic of red LD-pumped Q-switched alexandrite laser and cavity-dumping Q-switched alexandrite laser[53]
Fig. 14. Schematic of Q-switched diode-pumped alexandrite ring laser[55]
Fig. 15. Schematic of W-level Q-switched diode-pumped alexandrite ring laser[56]
Fig. 16. Setup of the experiment for LED-pumped alexandrite laser and the tunable multipass amplifier for a CW Ti:sapphire laser[59]
Fig. 19. Experimental setup for narrow linewidth alexandrite regenerative amplifier[66]
Fig. 20. Experimental setup for chirped pulse amplification of 300 fs pulses in an alexandrite regenerative amplifier[67]
Fig. 21. System schematic of the alexandrite-pumped alexandrite regenerative amplifier[68]
Fig. 22. Experimental setup diagram of dual-end-pumped alexandrite laser[81]
Fig. 23. Laser spectrum at maximum output power and beam qualities at different output powers[81]
Fig. 26. Multiphoton microscopy images of a mouse popliteal lymph node[112]
Table 1. The related thermo-mechanical parameters of the alexandrite, Ti:Sapphire, Cr:LiCAF, Cr:LiSAF, Cr:LiSGaF, and Yb:YAG crystal[17]
View tableView in ArticleTable 1. The related thermo-mechanical parameters of the alexandrite, Ti:Sapphire, Cr:LiCAF, Cr:LiSAF, Cr:LiSGaF, and Yb:YAG crystal[17]
Gain medium Cr3+:BeAl2O4 (Alexandrite) Ti3+:Al2O3 (Ti:sapphire) Cr3+:LiCaAlF6 (Cr:LiCAF) Cr3+:LiSrAlF6 (Cr:LiSAF) Cr3+:LiSrGaF6 (Cr:LiSGaF) Yb3+:Y3Al5O12 (Yb:YAG) Mass density ρ/(g·cm-3) 3.69 3.98 2.99 3.45 3.89 4.56 Melting point/°C 1 870 2 040 810 766 716 1 970 Specific heat capacity
Cp/(J·g-1·°C-1)
1.05 0.761 0.935 0.842 0.76 0.59 Mohs hardness 8.5 9 ~4 3~4 ~4 8.5 Knoop hardness/
(kg·mm-2)
1 600~2 300 1 800 (∥c)
2 200 (∥a)
- 197 - 1 320 Thermal conductivity
κ/(W·m-1·K-1)
23 (∥a-b-c) 30.3 (∥a)
32.5 (∥c)
4.58 (∥a)
5.14 (∥c)
1, 1.8 (∥a)
1.68, 3 (∥c)
1.3 (∥a)
2.6 (∥c)
10 Thermal expansion
coefficient
α/(×10-6K-1)
6 (∥a)
6 (∥b)
7 (∥c)
4.8 & 5.3 22, 21 (∥a)
3.6, 3.1 (∥c)
22.2, 25,
26 (∥a)
-9.8, -10,
-8.1 (∥c)
12, 23 (∥a)
0, -5.4 (∥c)
6.7 Thermal diffusivity
D/(×10-3 cm2·s-1)
60 92.5 16.4 (∥a)
18.4 (∥c)
6 (∥a)
10 (∥c)
4.4 (∥a)
8.8 (∥c)
37 Young modulus
E/(×109 Pa)
469 335 96 109 (avg)
85 (∥c)
120 (∥a)
- 280, 310 Poisson's ratio ν ~0.25 0.29 0.25 0.3 - 0.3 Tensile (fracture)
strength σf/(×106 Pa)
457~948 (∥a)
520 (∥b)
400 - 38.5±8 - 200 Fracture toughness
K1c/(×106 Pa·m1/2)
2.6 2.2 0.31,
0.18~0.37
0.33, 0.4 - 1.4 Thermal figure of merit
RT'/(W·m-1/2)
14 22 0.53 0.42 (∥a)
0.80 (∥c)
0.55 5.1 Damage threshold/
(J·cm-2)
270 @ 12 ns 7.8 @ 0.5 ps
80 @ 50 ps
210 @ 8 ns
20~25
@ 50 ps
1.5 @ 20 ps
8~24 @ 50 ps
20~26
@ 50 ps
110 @ 4.5 ns
Table 2. The spectroscopic and laser parameters of the alexandrite, Ti:Sapphire, Cr:LiCAF, Cr:LiSAF, Cr:LiSGaF, and Yb:YAG crystal[17]
View tableView in ArticleTable 2. The spectroscopic and laser parameters of the alexandrite, Ti:Sapphire, Cr:LiCAF, Cr:LiSAF, Cr:LiSGaF, and Yb:YAG crystal[17]
Gain medium Cr3+:BeAl2O4 (Alexandrite) Ti3+:Al2O3
(Ti:sapphire)
Cr3+:LiCaAlF6 (Cr:LiCAF) Cr3+:LiSrAlF6 (Cr:LiSAF) Cr3+:LiSrGaF6 (Cr:LiSGaF) Yb3+:Y3Al5O12 (Yb:YAG) Birefringence Biaxial Negative uniaxial Positive uniaxial Positive
uniaxial
Positive
uniaxial
Isotropic Refractive index n 1.736 7 (∥a) 1.742 1 (∥b) 1.734 6 (∥c) 1.765 5 (∥a)
1.757 3 (∥c)
1.380 (∥a)
1.380 8 (∥c)
1.387 3 (∥a)
1.394 0 (∥c)
1.389 3 (∥a)
1.391 (∥c)
1.82 Nonlinear refractive index n2/(×10-16 cm2·W-1) 2
3.54
3.2 0.4
0.36~0.66
0.8
0.52-2.15
1.2 6.9 Temperature dependence of refractive index
dn/dT/(×10-6 ·K-1)
5.5, 9.4 (∥a) 7, 8.3 (∥b) 14.9 (∥c) 13 4.2, -7.3 (∥a)
4.6, -4.9 (∥c)
-2.5, -4.5 (∥a)
-4, -9.1 (∥c)
-7, -2.7
(∥a)
-1.8 (∥c)
9.9 Group velocity dispersion/(fs2·mm-1) 60.7 56.6 24 22.7 ~25 66.6 Pump wavelength/nm 550 (∥a)
595 (∥b)
570 (∥c)
480 630 650 630 940 Absorption bandwidth/nm 90 (∥a)
80 (∥b)
70 (∥c)
125 90 100 85 12.5 Peak absorption cross section σab/(×10-20 cm2) 3.9 (∥a)
19 (∥b)
9 (∥c)
6.4 (∥c)
2.6 (∥a)
1.3 (∥c)
0.9 (∥a)
4.5 (∥c)
2.5 (∥a)
3 (∥c)
1.5 (∥a)
0.83 Maximum gain wavelength/nm 750 790 780 855 840 1 030 Tuning range/nm 714~818
(300 K)
660~1180 720~887 770~1 110 777~977 1 016~1 108 Peak emission cross section σem/(×10-20 cm2) 0.7 @ 22 °C 41 (∥c)
15 (∥a)
1.3 (∥c)
0.9 (∥a)
4.8 (∥c)
1.6 (∥a)
3.3 (∥c)
1.4 (∥a)
2.1 Room-temperature fluorescence lifetime τf /µs 262 3.2 175 67 88 940 σemτf/(×10-26 cm2·s) 183 @ 22 °C 131 228 322 290 1 975 Crystal figure of merit 3 000 150 2 150 3 300 ~2 000 - Gain saturation fluence
Jsat/(J·cm-2)
38 @ 22 °C 0.6 (∥c) 19.1 (∥c) 4.8 (∥c) 7.5 (∥c) 8.8
9.2
Table 3. The research progress of 640 nm red LDs
View tableView in ArticleTable 3. The research progress of 640 nm red LDs
Year Wavelength/nm Power/W Chip structure Institution 2008 643 12 0.4 mm bar, 20 emitting points,
40 µm×1.5 mm
Mitsubishi Electric Co., Japan[ 25 ]2012 635 1.2 5 µm×250 µm ridge-waveguide,
2 mm resonator
FBH, Germany[ 30 ]2014 639 2.3 Single emitting region,
150 µm×3 mm
nLight Co., US[ 29 ]2017 644 20.1 1 cm bar, 25 emitting points,
60 µm×0.7 mm
Sony Co., Japan[ 31 ]2018 638 6 Three emitting region,
180 µm×1.5 mm
Mitsubishi Electric Co., Japan [ 27 ]2019 638 4.5 Double emitting regions,
150 µm×1.5 mm
Ushio Opto Semiconductors Inc., Japan[ 28 ]2019 640 3.9 Single emitting region,
100 µm×1.5 mm
Huaguang Optoelectronics Co., China [ 32 ]
Table 4. Results of experiments based on flash lamp pumped alexandrite laser
View tableView in ArticleTable 4. Results of experiments based on flash lamp pumped alexandrite laser
Year Pump source Pump parameters Laser output performance Laser wavelength Ref. 1979 Xe flash lamp - 500 mJ, 200 µs; 70 mJ, 120 ns 701~794 nm [ 1 ]1980 Flash lamp 500 J, 1.5 kW 500 mJ, 33 ns, 5 Hz 701~818 nm [ 2 ]1980 Flash lamp 3.2 kW CW 6.5 W 765 nm 744~788 nm [ 36 ]1980 Flash lamp - 500 mJ, 20 ns 680.4 nm [ 38 ]1985 Hg arc lamp 6 kW CW 60 W - [ 18 ]1985 Xe arc lamp 8 kW CW 20W - [ 18 ]
Table 5. Results of continuous-wave alexandrite lasers (non-flashlamp pumping)
View tableView in ArticleTable 5. Results of continuous-wave alexandrite lasers (non-flashlamp pumping)
Year Pump source Pump
wavelength/nm
Pump power/W Slope
efficiency
Output power/W Tuning range/nm Remark 1983[ 39 ]Krypton ion laser 647.1 1.9 51% 0.6 726~802 Krypton ion laser pumping 1993[ 40 ]Dye laser 645 0.36 64% 0.15 753.4 Dye laser pumping 1993[ 40 ]Red LD 640 2×0.25 28% 0.025 753 - 2016[ 41 ]Green laser 532 11 26% 2.6 715~800 Green laser pumping 2006[ 42 ]Green laser 532 5 31% 1.4 730~780 - 1990[ 43 ]Red LD 680.4 0.01 25% - 751 First LD pumping 2005[ 11 ]Red LD 680.4 10 24% 1.3 750 - 2013[ 8 ]Red LD 680.4 0.865 34% 0.2 - - 2014[ 9 ]Red LD 639 64.5 49% 26 730~792 Highest output power
with LD pumping
2017[ 12 ]Red LD 638 56 37% 12.2 755.3 - 2020[ 14 ]Red LD 637 25 - 6.5 752 - 2018[ 47 ]Red LD 636 3.07 54.4% 1.22 714~818 Longest tuning range 2020[ 13 ]Red LD 636 34 54.9% 12.7 725~808 Highest slope efficiency
with LD pumping
2017[ 49 ]InGaN blue LD 444 3.5 20% 0.326 750 First blue LD pumping 2019[ 50 ]InGaN blue LD 445 3.5 39% 0.57 749.5 - 2020[ 16 ]Yellow laser 589 7.7 41% 2.51 727.2~787.3 First yellow laser pumping
Table 6. Results of Q-switched experiments based on alexandrite crystal
View tableView in ArticleTable 6. Results of Q-switched experiments based on alexandrite crystal
Year Pump source Q-switching Pulse energy Pulse width Repetition
frequency
Output
power
Ref. 2014 Red LD Pockels cell 0.74 mJ 92 ns 1 kHz 740 mW [ 9 ]2014 Red LD Pockels cell 0.7 mJ 58 ns 100 Hz 70 mW [ 9 ]2016 Red LD Pockels cell 0.8 mJ 350 ns 35 Hz 28 mW [ 52 ]2016 Red LD Pockels cell 6.2 mJ - 100 Hz 62 mW [ 52 ]2016 Red LD Pockels cell (cavity dumped) 510 µJ 3 ns Multi-kHz - [ 53 ]2018 Red LD SESAM 550 ns 27 kHz - [ 54 ]2018 Red LD Pockels cell 1 mJ 420 ns 150 Hz 150 mW [ 55 ]2018 Red LD Pockels cell 1.7 mJ 850 ns 500 Hz 850 mW [ 56 ]2019 Red LD Self-Q-switching 9.8 μJ 660 ns 135 kHz 1.32 W [ 57 ]
Table 7. Results of mode-locking experiments based on alexandrite crystal
View tableView in ArticleTable 7. Results of mode-locking experiments based on alexandrite crystal
Year Pump source Mode-locking Laser wavelength Pulse width Repetition
frequency
Output power Ref. 1982 Flash lamp Organic dye 725~745 nm 8 ps 12.5 Hz - [ 60 ]2016 532 nm laser KLM 755 nm 170 fs 80 MHz 780 mW [ 62 ]2018 532 nm laser QD-SESAM 775 nm 380 fs 79.9 MHz 295 mW [ 63 ]2018 532 nm laser KLM 750 nm 70 fs 5.6 MHz 4 mW [ 64 ]2018 532 nm laser Graphene 750 nm 65 fs 5.56 MHz 8 mW [ 65 ]
Table 8. The research progress of ultraviolet alexandrite laser
View tableView in ArticleTable 8. The research progress of ultraviolet alexandrite laser
Year Crystal Type Crystal dimensions Wavelength Pulse
energy
Pulse width Repetition frequency Highest
conversion efficiency/％
Ref. 1983 RDP Type I SHG 10 mm×10 mm×25 mm 0.36~0.40 µm 5 mJ 0.1 µs - - [ 69 ]1988 BBO Type I SHG 9 mm×5 mm×7 mm 378 nm 105 mJ - 4 Hz 31% [ 70 ]1989 BBO Type I SHG 4 mm×9 mm×7 mm 378 nm ~19 mJ - 10 Hz 26% [ 72 ]1989 BBO Type I THG 8 mm×4 mm×7.5 mm 252 nm ~7.5 mJ - 10 Hz 10%* [ 72 ]1994 BBO Type I SHG 8 mm 373 nm ~72 mJ - 60 Hz 28.6% [ 71 ]1994 KDP Type I THG - 248 nm 15 mJ - 100 Hz - [ 71 ]1998 BBO Type I SHG 5 mm×5 mm×5 mm 375 nm 90 mJ 240 µs 10 Hz - [ 73 ]2001 BBO Type I SHG 5 mm×5 mm×10 mm 365 nm 186 mJ 220 µs - 4.2% [ 74 ]2007 LBO Type I SHG 5 mm×4 mm×5 mm 0.36~0.388 µm 0.87 mJ - - 3.5% [ 75 ]2016 BBO Type I SHG 4 mm×4 mm×10 mm 379 nm 184 µJ - 1 kHz 47% [ 53 ]
Table 9. Some working lidars based on alexandrite lasers pumped by flashlamp[92]
View tableView in ArticleTable 9. Some working lidars based on alexandrite lasers pumped by flashlamp[92]
Property CNRS NASA MPI IAP Arecibo PNL Application DIAL DIAL DIAL Res fl Res fl Lab Seeder none none Ti:Al2O3 Diode Diode Diode Wavelength range /nm 727~732 725~785 720~780 770 770+385 750 Linewidth /MHz <560 560 <150 <20 <50 <20 Freq stability /MHz <110 <400 63 rms - - 16 Spectral purity >99.95% >99.85% >99.99% >99% - - Pulse width /ns <500 200 <200 275 100~300 140 Pulse energy /mJ 30 30 >50 100 200 250 Pulse rate /pps 20 10 >15 25 20 20 Installation Ground Aircraft Ground Ship Ground Ground
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Zhi-gang ZHAO, Chen GUAN, Zhen-hua CONG, Xing-yu ZHANG, Zhen ZHU, Shi-wu WANG, Yi NIE, Yang LIU, Zhao-jun LIU. Research Progresses of Alexandrite Solid-state Lasers （Invited）[J]. Acta Photonica Sinica, 2020, 49(11): 77
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Published Online: Mar. 11, 2021
The Author Email: LIU Zhao-jun (zhaojunliu@sdu.edu.cn)
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