Focusing 445nm Laser

[Brazil]

Hi,
I'm starting a research project and I will be in my tight budget until I have some preliminary results. I would appreciate any help or advice.

I bought a DHOM-I-445-600 (445nm / 600mW output / 2x4mm beam / Analog modulation).
I would like to focus it 200 microns depht inside a tissue.
I was thinking about using a lens with a focal lenght of some centimeters (let's say 10cm) and putting a glass window at 9.8cm in a way that when I place a tissue after the glass window, it will have the laser focused at 200 microns depth. I am also planning to use a kind of slide under the glass window, in a way that I can have precise micrometers movements.

I have some questions:
1 - Do I need to use a collimating lens before the focusing lens? (Laser specifications says it has a 2mrad divergence)
2 - What kind of lens do you recommend? ( I don't care to lose some power)
3 - How can I calculate the laser spot size and power at the focus point?

Thank you very much!

[mixedgas]

We're missing some data here... What is your desired focal spot size? What is your desired power density on target? 2 mR and blue diode means its difficult a to fix beam, which is why no one else has replied to you. Since your beam is not Gaussian by a long shot, it will be difficult to help you, and you may have to do this experimentally. We have no idea where you beam waist or origin is.

You may need to expand the beam before focusing it or to spatial filter the beam. Odds are you may need a microscope objective (cheap) rather then a singlet lens.

http://www.newport.com/store/genCont...ng/141191/1033

The reason you may or may not have problems is the emitter in the modern blue diodes is huge, and the initial divergence is extremely high.

Steve