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Pau Loong: Thank you for contacting Edmund Optics Technical Support, my name is Pau Loong; how can I help you today?
Nathan McCorkle: Hi, I need help finding the right optics for focusing a laser
Pau Loong: wavelength, divergence, raw beam diameter?
Nathan McCorkle: i desire a small spot size, but a close working distance (7-18 mm) is fine
Nathan McCorkle: one moment
Nathan McCorkle: its 405nm
Pau Loong: raw beam diameter?
Nathan McCorkle: i am not sure
Nathan McCorkle: i think about 2mm
Nathan McCorkle: but maybe 9mm
Nathan McCorkle: it is from a bluray 12X writer drive
Pau Loong: so you are looking for a single piece of focusing lens?
Nathan McCorkle: i saw these
Nathan McCorkle: what is the difference between the two?
Pau Loong: ok, for focusing a laser to a small spot size, we have to follow a equation
Pau Loong: spot size = wavelength * focal length / diameter * 4/pi
Nathan McCorkle: right
Nathan McCorkle: which is why I said a close focal length
Pau Loong: yes, you need to collimate the laser first, to make the beam parallel
Nathan McCorkle: the link i provided earlier, for the blue lenses?
Nathan McCorkle: said it was collimating
Nathan McCorkle: the assymetric one
Nathan McCorkle: (well there were multiple with different NAs)
Nathan McCorkle: coated/uncoated
Pau Loong: yes, you need to know the divergence of your laser
Pau Loong: then estimate the NA = 1 / 2 / f-number
Pau Loong: f-number = focal length / diameter
Nathan McCorkle: so if i setup my laser, what procedure could I perform to arrive with sufficient data?
Nathan McCorkle: i am assuming the raw diode will not have a focus
Pau Loong: wavelength, f-number
Pau Loong: that determine your final laser spot size
Nathan McCorkle: but if it doesn't have a focus, how can it have an f-number?
Nathan McCorkle: if its divergent out of the can
Pau Loong: your laser is diverging, so it has a f-number
Pau Loong: or NA
Pau Loong: NA = sin (half angle in degree)
Pau Loong: let me show you an illustration
Nathan McCorkle: so i would have to measure the spot size at multiple locations away from the exit hole in the diode can
Pau Loong:
Pau Loong: refer the Technical Images
Nathan McCorkle: to determine the angle
Pau Loong: right
Nathan McCorkle: does edmunds sell micrometers and mounts to help me with that?
Pau Loong: measure the angle found here:
Pau Loong: please have a sketch/drawing of your intended setup
Pau Loong: we can recommend from your sketch
Nathan McCorkle: hmm, ok
Nathan McCorkle: so once i determine the NA of the laser, and measure the width at the base... what can you recommend?
Pau Loong: yes
Nathan McCorkle: do I use the NA I determine and match a collimating lens of the same value?
Nathan McCorkle: the flat side up against the laser diode?
Pau Loong: the flat surface facing the laser
Nathan McCorkle: so that would produce a collimated beam, correct?
Pau Loong: right
Nathan McCorkle: and then I would need another lens to focus it?
Nathan McCorkle: what type of lens would that be?
Nathan McCorkle: i.e. the first type is an assymetric collimating lens
Pau Loong: depending on your Spot Size requirement, you might need to further expand your beam before focusing
Nathan McCorkle: i do not believe i need to expand the beam
Nathan McCorkle: when i calculated the spot size with the range of possible beam diameters
Nathan McCorkle: (I was assuming the beam was collimated)
Pau Loong: yes, but pay attention that f-number = focal length / diameter
Pau Loong: you can choose a lens with a fixed FL
Pau Loong: but how about the diameter?
Nathan McCorkle: is the diameter of the second lens based on the diameter of the beam out of the diode can?
Pau Loong: it is the Input to the focusing lens
Pau Loong: larger diameter gives you smaller spot size for a fixed FL
Nathan McCorkle: right, but if i get a 10mm diameter lens with 10mm focal length... will it perform the same as a 20mm diameter len, with a 10mm focal lenght
Nathan McCorkle: when i put the same 10mm collimated beam into them?
Pau Loong: certainly not
Pau Loong: pay attention to the formula of the spot size again
Pau Loong: you will have a spot size smaller by double if you double the diameter
Nathan McCorkle: i am talking about the diameter of the focusing len
Nathan McCorkle: s
Nathan McCorkle: not the collimated beam
Pau Loong: yes, i am assuming the diameter of the laser input same as diameter of the lens
Pau Loong: it is the laser diameter that concern
Nathan McCorkle: but if my laser diameter is 1.9mm and you only sell a 2mm diameter lens
Nathan McCorkle: then what is the effect?
Nathan McCorkle: does the spot size calculation use the lens diameter, or the beam diameter going into the lens (like i say the beam could be 1.9mm into a 2mm lens)
Pau Loong: the formula is for the laser diameter
Nathan McCorkle: ok so I just need to choose a lens larger than the beam, with the desired focal length?
Pau Loong: right
Nathan McCorkle: ahh, ok
Nathan McCorkle: so i need to match the NA of the laser to equal one of the asymmetric collimating lenses?
Pau Loong: it is Aspheric lens, not asymetric lens
Nathan McCorkle: i believe this may be correct
Nathan McCorkle: the beam divergence angles, of 8.5 degrees on horizontal direction and 19 degrees on vertical direction
Nathan McCorkle: ahh right, aspheric
Pau Loong: then you need to make your beam circular first
Pau Loong:
Nathan McCorkle: is it a problem to choose the larger divergence angle and use that for the NA calculation?
Pau Loong: yes, use the largest one if you plan to use an elliptical beam
Nathan McCorkle: hmm
Nathan McCorkle: how do i determine when the beam is mostly circular if I use the Anamorphic Prism Pairs
Pau Loong: check under the "Specifications" tab
Pau Loong: there is different magnifiation for different angle of adjustment
Nathan McCorkle: how would I mount the unmounted 405nm version
Nathan McCorkle: ?
Pau Loong: we don't have an empty mount to offer
Nathan McCorkle: !
Nathan McCorkle: so i have to machine something myself?
Pau Loong: it depends how you with to hold it
Pau Loong: wish
Nathan McCorkle: can you give me a link to the focusing lenses you think would be best?
Pau Loong: you must first determine the spot size you need
Nathan McCorkle: would it be plano convex?
Pau Loong: then we can determine the input diameter you need
Nathan McCorkle: or again an aspheric?
Nathan McCorkle: i need <= 5microns
Pau Loong: aspheric gives smaller spot size than PCX
Pau Loong: you can calculate the f-number based on the spot size equation
Nathan McCorkle: and i buy a lens by the F-number?
Pau Loong: f-number or NA, they are the same thing
Pau Loong: NA = 1/2/f-number
Nathan McCorkle: but for the spot size equation, I thought I just need to buy a lens based on the focal length
Pau Loong: spot size = 4/pi * f-number *wavelength
Nathan McCorkle: earlier you said "spot size = wavelength * focal length / diameter * 4/pi"
Pau Loong: yes, f-number = focal length / diameter
Nathan McCorkle: so i know its 405nm, its 2-3mm beam diameter, and I want something 7-17mm focal length to produce <= 5 micron spot size
Nathan McCorkle: so can i just choose a lens based on focal length?
Pau Loong: you cannot choose diameter and focal length by yourself
Pau Loong: it is determine by the formula
Nathan McCorkle: earlier you said "Pau Loong: the formula is for the laser diameter"
Pau Loong: you need to calculate the focal length you need
Nathan McCorkle: why, I have calculated that a range from 7-17mm will produce a spot sufficient for my purposes
Pau Loong: ok, if you have calculated, then you can choose the Aspheric lens
Nathan McCorkle: link please?
Pau Loong:
Pau Loong: and
Pau Loong:
Nathan McCorkle: and do you sell the mounting track, to place items next to each other?
Nathan McCorkle: are those "Precision Molded Aspheric Lenses" glass or plastic?
Pau Loong:
Pau Loong: glass
Nathan McCorkle: ok, well I think that's enough info for tonight, I will try to find the information on the laser, and if I can't, I will have to measure it
Nathan McCorkle: thanks a lot
Pau Loong: If you have any further questions our Technical Support Department is here Sunday 8:00 pm through Friday 6:00 pm EST.
Pau Loong: Thank you for contacting Edmund Optics!