The author has acquired a yellow laser with the specific wavelength of 589 nm. Because this is the first time such a laser has been discussed in this journal, I feel it is appropriate to provide a discussion of its function and capabilities. Normal laser safety should be employed, such as not pointing it into eyes or at people, and using eye protection for the young and inexperienced. It is important to note that 589 nm is the same wavelength as the Sodium-D line (doublet). This allows for the laser to serve as a replacement for sodium lamps, and, considering its rather high price, this added value should be balanced against its cost. What follows is a list of activities that showcase the yellow laser’s unique promise as an engaging piece of technology that can be used in the teaching of physics.

1.
With a little shopping around, I managed to get one for \$330. I hope and expect the price to drop in the future.
2.
I chose this laser to celebrate its unique wavelength’s properties, but the yellow laser is not new, just new to The Physics Teacher. For example, see
Christopher
Hopper
and
Andrzej
, “
Yellow He–Ne going red: A one-minute optics demonstration
,”
Am. J. Phys.
76
,
596
(
June
2008
).
3.
Allow its beam to land on a wall that is a measured distance L away. The first dispersed laser dot will be a distance y from the central dot. Based on the angle of dispersion θ one can measure the wavelength λ using d sin θ = mλ, where m = 1 for the first-order diffraction. I usually calculate the angle using θ = tan−1 (y/L) because y and L are so easy to measure. Or, to save time, approximate that sin θy/L.
4.
For a similar demo, and a good discussion about human color vision, see
Lars-Jochen
Thoms
,
Giuseppe
Colicchia
, and
Raimund
Girwidz
, “
Color reproduction with a smartphone
,”
Phys. Teach.
51
,
440
(
Oct.
2013
).
5.
Proof that yellow is not equivalent to red and green is well illustrated in
Cortel
, “
Yellow: The magic color
,”
Phys. Teach.
46
,
121
(
Feb.
2008
).
6.
The demo is usually performed with a sodium lamp. For example, see
Michael
Gore
, “
Shedding light on darkness
,”
Phys. Teach.
45
,
250
(
April
2007
).
7.
These dark stripes are called Fraunhofer lines, https://en.wikipedia.org/wiki/Fraunhofer_lines.
8.
R
Weuker
,
AY
Wong
,
M
Simon
,
T
Fukuchi
, “
Lidar tuning with a Na lamp
,”
Opt Eng.
36
(
1
)
146
149
(
Jan.
1997
).