PASSIVELY Q-SWITCHED LASER
Passively Q-switched lasers and short wave infrared (SWIR) electro-optical systems including such lasers. A passively Q-switched laser may include a gain medium (GM) having a stimulated emission cross section σ SE , a saturable absorber (SA) having an absorption cross section (σ a ) which is less than three times the σ SE of the GM, and an optical resonator within which the GM and the SA are positioned, the optical resonator comprising a high reflectivity mirror and an output coupler, wherein at least one of the high reflectivity mirror and the output coupler comprises a curved mirror, directing light within the optical resonator such that an effective cross-section of a laser mode within the SA (A SA ) is smaller than a cross-section of a laser mode within a Rayleigh length of the pump (A GM ).
1 . A gain medium amplifier, the gain medium amplifier comprising:
a flat neodymium-doped yttrium aluminum garnet (Nd:YAG) crystal, having an average thickness of less than 5 millimeters, the flat Nd:YAG crystal comprising:
a top surface through which pump light having a first frequency enters the flat Nd:YAG crystal, the first frequency being between 750 nanometer (nm) and 850 nm, wherein the top surface has a first dimension and a second dimension orthogonal to the first dimension, and wherein the first dimension is at least 5 times longer than the average thickness of the flat Nd:YAG crystal;
a bottom surface opposing the top surface;
a first side surface, through which incoming laser light having a second frequency enters the flat Nd:YAG crystal, the second frequency being between 1,300 nm and 1,400 nm; and
a second side surface through which outgoing laser light having an emitted light frequency is emitted from the flat Nd:YAG crystal after being reflected by multiple different sides surfaces of the flat Nd:YAG crystal, wherein a power of the outgoing laser light is at least 2 times stronger than a power of the incoming laser light after being amplified using the pump light.
2 . The gain medium amplifier of claim 1 , wherein the emitted light frequency is substantially the same as the second frequency.
3 . The gain medium amplifier of claim 1 , wherein the average thickness is between 0.5 mm and 2 mm.
4 . The gain medium amplifier of claim 1 , wherein the second dimension is at least 3 times longer than the average thickness.
5 . The gain medium amplifier of claim 1 , wherein the second dimension is at least 5 times longer than the average thickness.
6 . The gain medium amplifier of claim 1 , wherein a doping concentration of the Neodymium within the flat Nd:YAG crystal is lower than 4%.
7 . The gain medium amplifier of claim 1 , wherein a doping concentration of the Neodymium within the flat Nd:YAG crystal is between 1% and 2%.
8 . The gain medium amplifier of claim 1 , wherein the top surface is coated with anti-reflective coating for at least one frequency out of: the first frequency, the second frequency, and the emitted light frequency.
9 . The gain medium amplifier of claim 1 , wherein the top surface is coated with anti-reflective coating for at least two frequencies out of: the first frequency, the second frequency, and the emitted light frequency.
10 . The gain medium amplifier of claim 1 , wherein at least one of the first side surface and the second side surface is coated with anti-reflective coating for at least one frequency out of: the first frequency, the second frequency, and the emitted light frequency.
11 . The gain medium amplifier of claim 1 , wherein at least one of the first side surface and the second side surface is coated with anti-reflective coating for at least two frequencies out of: the first frequency, the second frequency, and the emitted light frequency.
12 . The gain medium amplifier of claim 10 , wherein the at least one of the first side surface and the second side surface is further coated with anti-reflective coating for an amplified spontaneous emission (ASE) frequency of the flat Nd:YAG crystal.
13 . The gain medium amplifier of claim 11 , wherein the at least one of the first side surface and the second side surface is further coated with anti-reflective coating for an amplified spontaneous emission (ASE) frequency of the flat Nd:YAG crystal.
14 . The gain medium amplifier of claim 1 , wherein a doping density of the flat Nd:YAG crystal is higher than 1%.
15 . The gain medium amplifier of claim 1 , comprising a cooling module touching the bottom surface, for removing from the flat Nd:YAG crystal heat introduced by the pump light.
16 . The gain medium amplifier of claim 1 , wherein light entering the flat Nd:YAG crystal via the first side surface is emitted along at least 80% of its optical path before being emitted via the second side surface.