Laser pointer experiments

> Pointers are now a cheap commodity item and, although the
> quality is pretty variable, most can be persuaded to produce a
> spot at least as good as the centre/edge finder versions.
>
> The pointers incorporate three main items plus the
> battery.
>
> The laser diode itself which is a near "point" source and emits a
> diverging beam.
>
> A lens which changes this diverging beam to a collimated beam
> (i.e. a parallel beam focussed at infinity)
>
> A small bunch of electronics which monitors the beam intensity
> and keeps it safely below laser diode burnout point independent
> of battery voltage and laser temperature.
>
> This is all organised to produce the brightest possible
> beam. For center/edge finder work this is far too bright and
> neutral density filters or crossed polaroids are commonly used to
> reduce this to a manageable level. Without these, because the eye
> saturates, the spot appears much larger
>
> Another way of reducing brightness is to add a series
> resistor to the battery to reduce the operating current
> (typically 150mA). The amount required is dependent on the laser
> characteristics - the useful range is about 50 to 500 ohms. In
> adding wires to the pointer be sure to remember that the metal
> case is POSITIVE.
>
> A second change is to refocus the lens to produce its
> focussed image at a more useful distance. The lens is normally in
> a threaded metal mount which can be rotated to alter focus.
> Because the initial beam diameter is small, the depth of focus is
> large and not critically dependent on the distance to the image
> point. The lens position needs to be typically 30% to 50% further
> away from the laser diode.
>
> Changing the lens position is the best option but it can
> be a fiddly business. Much the same result can be obtained by
> adding a second lens. Because the initial beam is parallel the
> position of this lens is not critical - close to the existing
> lens is convenient.
>
> Ideally it should be plano convex with the convex side
> facing the existing laser lens but the the biconvex lens fitted
> many eye loupes performs pretty well. The focal distance depends
> on the power of the eye loupe - a x5 loupe has a focal length of
> 2" and this is a convenient working distance. Higher power loupes
> produce proportionately smaller working distance and spot size.
>
> This reduction in spot size produces a substantial
> increase in brightness so reduction of beam power is essential to
> prevent eye saturation effects.
>
> This spot is now a LOT smaller than the original short
> range pointer collimated beam but, because it is now an image of
> the actual emitting surface of the laser, the shape can be a bit
> variable dependent on the particular laser diode. Two out of
> three laser pointers produced acceptably shaped spots the third
> produced an odd shaped elongated spot. Some improvement should be
> possible with a strategically placed pinhole but I've not tried
> this. The best pinhole position is likely to be very close the
> the laser diode window. It's not easy to mount here and it would
> require accurate alignment of the pinhole position.
>
> It's pretty easy to check out the odd pointer so it
> would be interesting to learn how well different pointers
> performed and whether pinholes are a practicable improvement.
>
>
> Jim

> Pointers are now a cheap commodity item and, although the
> quality is pretty variable, most can be persuaded to produce a
> spot at least as good as the centre/edge finder versions.
>
> The pointers incorporate three main items plus the
> battery.
>
> The laser diode itself which is a near "point" source and emits a
> diverging beam.
>
> A lens which changes this diverging beam to a collimated beam
> (i.e. a parallel beam focussed at infinity)
>
> A small bunch of electronics which monitors the beam intensity
> and keeps it safely below laser diode burnout point independent
> of battery voltage and laser temperature.
>
> This is all organised to produce the brightest possible
> beam. For center/edge finder work this is far too bright and
> neutral density filters or crossed polaroids are commonly used to
> reduce this to a manageable level. Without these, because the eye
> saturates, the spot appears much larger
>
> Another way of reducing brightness is to add a series
> resistor to the battery to reduce the operating current
> (typically 150mA). The amount required is dependent on the laser
> characteristics - the useful range is about 50 to 500 ohms. In
> adding wires to the pointer be sure to remember that the metal
> case is POSITIVE.
>
> A second change is to refocus the lens to produce its
> focussed image at a more useful distance. The lens is normally in
> a threaded metal mount which can be rotated to alter focus.
> Because the initial beam diameter is small, the depth of focus is
> large and not critically dependent on the distance to the image
> point. The lens position needs to be typically 30% to 50% further
> away from the laser diode.
>
> Changing the lens position is the best option but it can
> be a fiddly business. Much the same result can be obtained by
> adding a second lens. Because the initial beam is parallel the
> position of this lens is not critical - close to the existing
> lens is convenient.
>
> Ideally it should be plano convex with the convex side
> facing the existing laser lens but the the biconvex lens fitted
> many eye loupes performs pretty well. The focal distance depends
> on the power of the eye loupe - a x5 loupe has a focal length of
> 2" and this is a convenient working distance. Higher power loupes
> produce proportionately smaller working distance and spot size.
>
> This reduction in spot size produces a substantial
> increase in brightness so reduction of beam power is essential to
> prevent eye saturation effects.
>
> This spot is now a LOT smaller than the original short
> range pointer collimated beam but, because it is now an image of
> the actual emitting surface of the laser, the shape can be a bit
> variable dependent on the particular laser diode. Two out of
> three laser pointers produced acceptably shaped spots the third
> produced an odd shaped elongated spot. Some improvement should be
> possible with a strategically placed pinhole but I've not tried
> this. The best pinhole position is likely to be very close the
> the laser diode window. It's not easy to mount here and it would
> require accurate alignment of the pinhole position.
>
> It's pretty easy to check out the odd pointer so it
> would be interesting to learn how well different pointers
> performed and whether pinholes are a practicable improvement.
>
>
> Jim

> I'm not sure how you plan to use these but may be able to help as I've
> played around with laser pointers for a good few years now and hang out at=

> alt.lasers and sci.optics quite a bit.
>
> Given the low power requirements I'm guessing you'll want to use red laser=

> diode based pointers at around 650nm or 635nm. These do produce a far from=

> circular spot. Given the low power requirements for this application the
> easiest solution is to use a suitable round aperture in the light path as
> mentioned. I can't see that any benefit will be gained from placing a tiny=

> aperture near to the laser diode itself. I'd have thought either side of t=

> collimating lens is best. In fact normally the lens is actually smaller th=

> that required to capture the entire diode output so it already acts to
> partially clean up the beam shape by excluding the extreme ends of the (ve=

> roughly) rectangular beam.
>
> Cheap laser pointer tend to have a bare laser diode without a windowed
> containing package.
>
> Laser diodes are very susceptible to static electricity or overpowering ev=

> for short durations. Bear this in mind if you plan to rewire one.
>
> Hope this is of use,
>
> Scrim
>
>
>
>
>

> > Pointers are now a cheap commodity item and, although the
> > quality is pretty variable, most can be persuaded to produce a
> > spot at least as good as the centre/edge finder versions.

>

> > =A0 =A0 =A0 The pointers incorporate three main items plus the
> > battery.

>

> > The laser diode itself which is a near "point" source and emits a
> > diverging beam.

>

> > A lens which changes this diverging beam to a collimated beam
> > (i.e. a parallel beam focussed at infinity)

>

> > A small bunch of electronics which monitors the beam intensity
> > and keeps it safely below laser diode burnout point independent
> > of battery voltage and laser temperature.

>

> > =A0 =A0 =A0 =A0 This is all organised to produce the brightest possible
> > beam. For center/edge finder work this is far too bright and
> > neutral density filters or crossed polaroids are commonly used to
> > reduce this to a manageable level. Without these, because the eye
> > saturates, the spot appears much larger

>

> > =A0 =A0 =A0Another way of reducing brightness is to add a series
> > resistor to the battery to reduce the =A0operating current
> > (typically 150mA). The amount required is dependent on the laser
> > characteristics - the useful range is about 50 to 500 ohms. In
> > adding wires to the pointer be sure to remember that the metal
> > case is POSITIVE.

>

> > =A0 =A0 =A0 =A0 =A0A second change is to refocus the lens to produce its=

> > focussed image at a more useful distance. The lens is normally in
> > a threaded metal mount which can be rotated to alter focus.
> > Because the initial beam diameter is small, the depth of focus is
> > large and not critically dependent on the distance to the image
> > point. The lens position needs to be typically 30% to 50% further
> > away from the laser diode.

>

> > =A0 =A0 =A0 =A0 Changing the lens position is the best option but it can=

> > be a fiddly business. Much the same result can be obtained by
> > adding a second lens. Because the initial beam is parallel the
> > position of this lens is not critical - close to the existing
> > lens is convenient.

>

> > =A0 =A0 =A0 Ideally it should be plano convex with the convex side
> > facing the existing laser lens but the the biconvex lens fitted
> > many eye loupes performs pretty well. The focal distance depends
> > on the power of the eye loupe - a x5 loupe has a focal length of
> > 2" and this is a convenient working distance. Higher power loupes
> > produce proportionately smaller working distance and spot size.

>

> > =A0 =A0 =A0 =A0 =A0This reduction in spot size produces a substantial
> > increase in brightness so reduction of beam power is essential to
> > prevent eye saturation effects.

>

> > =A0 =A0 =A0 =A0 =A0This spot is now a LOT smaller than the original shor=

> > range pointer collimated beam but, because it is now an image of
> > the actual emitting surface of the laser, the shape can be a bit
> > variable dependent on the particular laser diode. Two out of
> > three laser pointers produced acceptably shaped spots the third
> > produced an odd shaped elongated spot. Some improvement should be
> > possible with a strategically placed pinhole but I've not tried
> > this. The best pinhole position is likely to be very close the
> > the laser diode window. It's not easy to mount here and it would
> > require accurate alignment of the pinhole position.

>

> > =A0 =A0 =A0 =A0 =A0 =A0It's pretty easy to check out the odd pointer so =

> > would be interesting to learn how well different pointers
> > performed and whether pinholes are a practicable improvement.

>

> > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0Jim- Hide quo=

>
> - Show quoted text -

>Not wishing to detract anything said, might I mention that a series
>ran in Model Engineers Workshop.