Welcome to Laser Pointer Forums - discuss green laser pointers, blue laser pointers, and all types of lasers

LPF Donation via Stripe | LPF Donation - Other Methods

Links below open in new window

ArcticMyst Security by Avery

One question about DPSS lasers

Joined
May 20, 2012
Messages
36
Points
6
I'm a laser newbie, so I don't know how exactly DPSS lasers work but here's the question.


I have bought many green laser pens in the past and I have noticed something that called my attention: The time it takes to some green lasers to brighten up.

I've had green laser pens that would basically reach the maximum power as soon as you turned it on (almost instant), but there were others that would take a second or two to fully reach the maximum brightness and I was wondering if someone here could answer me why it happens or if it has something to do with laser duty cycles, their modules, diodes etc...


Kind of confused, please clarify.


Thanks in advance.
 
Last edited:





diachi

0
Joined
Feb 22, 2008
Messages
9,700
Points
113
I'm a laser newbie, so I don't know how exactly DPSS lasers work but here's the question.


I have bought many green laser pens in the past and I have noticed something that called my attention: The time it takes to some green lasers to brighten up.

I've had green laser pens that would basically reach the maximum power as soon as you turned it on (almost instant), but there were others that would take a second or two to fully reach the maximum brightness and I was wondering if someone here could answer me why it happens or if it has something to do with laser duty cycles, their modules, diodes etc...


Kind of confused, please clarify.


Thanks in advance.

It's to do with how DPSS lasers work - They use a couple of crystals to convert 808nm pump light into some other frequency, in the case of green it is usually 808nm->1064nm->532nm.

See this diagram:

l54-101.gif


There are a couple of temperature sensitive components here, the KTP which needs to be at a specific temperature for good efficiency, and the diode which also needs to be at a specific temperature to maintain the 808nm output.

If the temperature of the KTP isn't correct the efficiency can be dramatically reduced. Similarly, if the diode is not at the correct temperature then it can shift wavelength slightly (By a few nm in either direction), meaning that it isn't absorbed as well by the Nd:YVO4 which has a fairly narrow absorption band around 808nm.

As can be seen with this graph:

20110425091130578.jpg



I hope this clears up some confusion, let me know if you need a different explanation or have any questions!
 
Joined
May 20, 2012
Messages
36
Points
6
Oh, since there are temperature-sensitive components inside the module, temperature plays an important role in DPSS lasers right?

(Correct me if I'm wrong)


EDIT:

Is the KTP crystal responsible of its' green color? (532nm)
 
Last edited:
Joined
Jan 14, 2009
Messages
1,452
Points
83
Oh, since there are temperature-sensitive components inside the module, temperature plays an important role in DPSS lasers right?

(Correct me if I'm wrong)


EDIT:

Is the KTP crystal responsible of its' green color? (532nm)

temperature has a very large impact on the performance of the DPSS process .

The KTP if responsible for SHG , In a 532nm laser the KTP is responsible for combining 2 photons of 1064nm light into one 532nm photon ( twice the energy )

The 1064nm is generated by a ND:YAG or ND:YVO4 Crystal that is pumped by 808nm .
 

diachi

0
Joined
Feb 22, 2008
Messages
9,700
Points
113
temperature has a very large impact on the performance of the DPSS process .

The KTP if responsible for SHG , In a 532nm laser the KTP is responsible for combining 2 photons of 1064nm light into one 532nm photon ( twice the energy )

The 1064nm is generated by a ND:YAG or ND:YVO4 Crystal that is pumped by 808nm .

Thanks for adding the clarification! :)

I should add, Nd:YVO4 is a little less fussy about the pump wavelength compared to Nd:YAG, which has a somewhat narrower absorption band centred around 808nm.
 
Last edited:
Joined
May 20, 2013
Messages
358
Points
28
I had one laser that need up to 2 minutes on to reach full power, that's because of another characteristic of DPSS lasers: mode hopping.

It is very complicated but interesting, happens when the crystals expands during warm up time, the beam changes shapes and the output power suffer from big fluctuations until the correct temperature is reached.
 

diachi

0
Joined
Feb 22, 2008
Messages
9,700
Points
113
I had one laser that need up to 2 minutes on to reach full power, that's because of another characteristic of DPSS lasers: mode hopping.

It is very complicated but interesting, happens when the crystals expands during warm up time, the beam changes shapes and the output power suffer from big fluctuations until the correct temperature is reached.

Actually, other types of lasers can mode hop too. Solid state, direct diode (IIRC), gas etc. It can happen for different reasons - bad alignment and thermal lensing among other reasons. Although I'd hazard a guess that it's more common with DPSS.
 




Top