two optics-related questions (crystal assemblies and coatings)

[ixfd64]

One thing I love about LPF is that it's always a great source of information! Anyways, I have couple more questions:

1. I've noticed that crystals in DPSS lasers can be bonded or discrete. It seems that crystals in small lasers tend to be bonded, while those in higher-powered lasers are not. According to my research, the reasons that crystals are not bonded in high-powered lasers are that 1) optical bondings are easily damaged by high-powered lasers, and that 2) separating crystals makes it easier to heatsink them via TEC. However, from what I gather, bonded crystals are easier to work with. Are there any other advantages of using bonded/discrete crystals?

2. I know that DPSS lasers require optical cavity mirrors. It seems that the "mirrors" in most modern lasers are nothing more than an optical coating on one side of a crystal. However, many optical coatings have a lower damage threshold than the crystal on which they're applied. In the case of high-powered lasers, would "traditional" mirrors be used instead?

By the way, I've recently made a lot of additions to the Wikipedia article on DPSS lasers in hopes that other people will find them useful. Feel free to make corrections as you see fit.

 

[Bluefan]

An important point is the damage threshold of the bonding material, I think I read somewhere that this can be a limiting for the maximum power.

In higher power DPSS lasers the different crystals are kept at a different temperature, which is not possible when they are bonded. Things like q-switches, brewster angle plates are not possible when you bond the crystals, or try making a ring laser.

It's also practical not to have the mirrors coated in the separate crystals, because then the whole crystal + cooling assembly will have to be adjustable, so probably lasers with separate crystals will have discrete mirrors.

 

[LSRFAQ]

Two things,

One, You cannot neglect the fact that the materials expand at different rates.

Two, The best, high power, bonded crystals (MCAs) do not involve glue, but use molecular bonding, created with high temperatures and electrostatic fields.

Steve

 

[goninanbl00d]

One thing I love about LPF is that it's always a great source of information! Anyways, I have couple more questions:

1. I've noticed that crystals in DPSS lasers can be bonded or discrete. It seems that crystals in small lasers tend to be bonded, while those in higher-powered lasers are not. According to my research, the reasons that crystals are not bonded in high-powered lasers are that 1) optical bondings are easily damaged by high-powered lasers, and that 2) separating crystals makes it easier to heatsink them via TEC. However, from what I gather, bonded crystals are easier to work with. Are there any other advantages of using bonded/discrete crystals?

2. I know that DPSS lasers require optical cavity mirrors. It seems that the "mirrors" in most modern lasers are nothing more than an optical coating on one side of a crystal. However, many optical coatings have a lower damage threshold than the crystal on which they're applied. In the case of high-powered lasers, would "traditional" mirrors be used instead?

By the way, I've recently made a lot of additions to the Wikipedia article on DPSS lasers in hopes that other people will find them useful. Feel free to make corrections as you see fit.

Bonded crystals are only easier to work with in the fact that the YVO4 and KTP do not need to be individually phase-matched, and that only one mount is needed for both crystals.

Crystal sets can also be heatsinked- however, YVO4 prefers to be cooled, and KTP prefers to be heated. This is the reason why in higher-end lasers, two TECs are used.

Bonded crystals are more affected by the effects of thermal expansion and stress than discrete crystals. The crystals expand at different rates, causing possible alignment shifts.

Discrete output couplers are also used for stability reasons (along with power concerns). As the optic has its own mount, it is not affected by changes within the crystals, and by the expansion/contraction of the crystals during operation.

This is the reason why the larger 25mm green modules often have discrete output couplers, mounted seperately and at a distance from the crystal set.