REVIEW of Gogu's AO modulators and Crystalaser DPSS lasers

[shrad]

Hi everyone!

I wanted to review gogu's products (should have done that long ago, sorry go)

First, the AO modulators

He sells either AA Optics modulators and drivers or isomet 1205-c modulators and drivers

These two AOMs are designed for visible wavelengths and will work great from 420-ish nanometers to the far visible region (near 700nm)

AA Optics driver :


AA Optics modulator :


As people here have already purchased such units from him, they will agree the device comes in perfect state, near new condition

As fas as I know, there is still a problem with such devices, it is the ability to adjust them along the optical axis to get the best diffraction (Bragg angle)

This is somewhat tricky as it is a matter of maybe half a degree for an efficiency difference of easily 10% (so to achieve highest diffraction efficiency, you need to adjust the angle +/- a fraction of a degree around bragg angle)

As for these "solar system" shaped artefacts you can see when using these, as fas as I know they will always be present but are really a small portion of the incoming power, so may be neglected as they will never get out of a projector (if your beam is hitting a mirror, these patterns will likely be out of the mirror area after a couple reflections)

If these patterns really are too strong, one could reduce the RF power applied to the modulator by tweaking the power adjust on the driver, but much care has to be observed when doing this as you could fry the poor crystal

With these, I achieved an overall 60% deflection efficiency at 28VDC supply voltage (be sure to have at least 500mA) and 0-5V modulation input... lack of instrumentation and mounting hardware prevented me to achieve perfect tweaking, as they are really sensible (you have to mount the AO modulator away from heat sources as a small thermal expansion of its mount can mean an efficiency drop of like 10%, so maybe a subplate with a TEC would be nice)

What I'm sure is these AOMs could easily achieve 80% efficiency with proper hardware, polarization and careful design and tweaking - not easy with my scrap-bin hardware

Following are links to youtube videos I made from the modulated beam of a Crystalaser DPSS from him, at frequencies of 1Hz, 5Hz and 10Hz (will go up to the megahertz range, but over 10Hz the camera didn't pick up anything more than a slight flickering)

Here is the AO modulated beam at 1Hz:


Here is the AO modulated beam at 5Hz:


Here is the AO modulated beam at 10Hz:


And finally, a video of the artefacts commonly encountered with AO modulators (if someone has hints about how it could be avoided expect with quality bragg mounts, please tell):



Second: the Crystalaser DPSS units

These DPSS units are GREAT!

They are dual TEC units with high stability regulation, thermal protection and overheat indication, they have beam correction optics (wedge pair) and an IR filter

Those lasers are really neat, they are SINGLE MODE and ULTRA STABLE, perfect for holography

The only drawback for show use are the beamspecs, less than 0.5mm diameter with several millirads at the aperture, but one could find means of reducing divergence (like a 1:4 telecope to get a 2mm dia beam with less than 1 millirad divergence)

I modified the collimation lens distance from this one to get a spot of 3 centimeters 5 meters away (from the original 6 centimeters)

Here are some pictures:

The unit close to the dual red I built from Pat's hardware :
]

The beam compared to the one of the red unit :


All in all, Gogu has some nice stuff, for a really nice price, so if you need such items you should go for it!

Any comments are welcome about the AO modulators and the way to use them, as there are for sure members here with a greater experience than mine

[sugeek]

In addition to shrad I have an AA AOM and a crystalaser from gogu, as shrad has noted they come in excellent condition and are a pleasure to work with. They do need adjustment to get the optimum output, and additional tuning of the driver is possible with and RF power meter, there is more information from Steve (mixedgas) has posted in another thread. A couple of pictures for fun!

-Adam

[-bart-]

but much care has to be observed when doing this as you could fry the poor crystal

clock-wise = less power
anti-clock-wise = more power

[shrad]

I tried it out, it gave the same artefacts, but I'll try to get better hardware and retry

[mixedgas]

How do you know they are single mode and work for Holo? Have you tried it? Got a picture of the cavity?

Steve

[sugeek]

How do you know they are single mode and work for Holo? Have you tried it? Got a picture of the cavity?

Steve

There you go Steve.

[-bart-]

I think there might be some confusion on the term "single mode".
link
Usually when a dpss laser is called single mode, it has some form of mode locking, I don't see that happening in your cavity.

Nice laser though!

[shrad]

maybe I was too fast stating they are single mode, according to this page (http://www.crystalaser.com/new/greenlaser.html) they are model xxxx-L which is low noise version, so not the single mode version