Monica Rambeau was a lieutenant in the New Orleans Harbor Patrol. Fate came upon her one day, when she gained super powers after being bombarded by extradimensional energy, produced by an energy disruptor weapon created by a criminal scientist.
She was originally given the name of Captain Marvel by the media. After her initial appearance, Rambeau began experimenting with her powers. Early in her career, she met Spider-Man, who was kind enough to introduce her to the Avengers for additional training. As Captain Marvel, she joined and served in the Avengers. Her membership was a lengthy stint, during which she eventually became the team's leader. Because of injuries, she was forced to leave the active roster. Being off the active roster, she became one of the team's more reliable reservists. Subsequently, she found herself assuming leadership, on two occasions.
Monica was known as Captain Marvel for most of her Avengers career; however, she agreed to change her alias to Photon, conceding the Captain Marvel title to Genis-Vell, the son of the original Captain Marvel, out of respect for her predecessor. 
Members included Rambeau, a man known only as "the Captain", Boom-Boom, Aaron Stack, and Elsa Bloodstone. Monica annoyed all of her teammates by constantly bringing up her past experience leading the Avengers (which Aaron mocked by having his LMD of Monica repeat it in a weeping voice), and she had developed a penchant for shouting the names of her energy attacks.
It has since been implied that all of Monica's experiences with Nextwave were a fiction implanted in her mind by the Beyond Corporation, and Monica angrily claimed she spent a year remembering events that never happened. 
Monica briefly fought the man known as Bluestreak in a new costume. An onlooking cop said to him, "Geez, where you been, Losing Streak? Don'cha read the magazines? She's called Spectrum now." She then returned to the shop where it was made, and helped Spider Hero suit up for the battle. She arrived in New York City to fight Proxima Midnight.  She was hit by Proxima's spear and incapacitated but she was returned to normal by Blue Marvel. She tried to mimic Shuma-Gorath's shield in her light form to buy time, and caused him to explode by manipulating his brain electricity. She was among the people declared Avengers by Luke Cage. 
Energy Form: Due to bombardment by extra-dimensional energies, Monica can transform herself into any form of energy within the electromagnetic spectrum. Among the many energy forms she has assumed and is able to control are cosmic rays, gamma rays, X-rays, ultraviolet radiation, visible light, electricity, infrared radiation, microwaves, radio waves and neutrinos. She apparently accomplished this transformation by mentally shunting the matter of her body into the dimension from which she draws her energy, and replacing it with a corresponding amount of energy. Her mind remains in the dimension to control the energy-parcel that has taken the place of her body. By assuming an energy-form, she gains all of that energy's properties. Monica is apparently unlimited by the amount of time that she can remain in her energy-form. She can seemingly only transform herself into one wavelength of energy at a time, but she can transform between one energy-state and another in a fraction of a second. As noted above, the limit to the amount of energy she can transmit through her body at a given time is not known. Extensive energy transformation and manipulation can be physically taxing once she returns to her physical form.
Flight: she is capable of flight in any of her wavelengths.
Superhuman Speed: Monica is cable of moving and reacting at superhuman speeds ranging from the speed of sound to lightspeed.
Intangibility She can phase through solid matter and certain energy fields depending on its wavelength.
Invisibility: She is often invisible in most of her forms but can make herself appear visible.
Energy Duplication: When she encounters a new or unfamiliar energy, Monica can often duplicate it given enough time for analysis.
Energy Absorption: She is capable of absorbing energy given her own energy form is at the right wavelength.
Energy Blasts: She mentally controls both type and quantity of energy she wishes to transmit. It is not known the maximum amount of energy she can transmit at a given time. Monica can also divert small amounts of various energies for employment as force beams, which have the equivalent to 300 tons of TNT of explosive force.
Appearance Alteration: Monica can use her powers to modulate her energy and modify her appearance, and take the form of other people. However, when she does so, she doesn't actually change her physical shape.
Eidetic Memory: Ever since she acquired her powers, Monica's photographic memory improved, allowing her to have totall recall of everything she sees.
Skilled Leader: Monica has strong leadership skills and law enforcement experience. Expert Combatant: She is an excellent marksman and unarmed combatant due to her law enforcement training. Skilled Detective Strong Swimmer
Normal human female with moderate regular exercise.
Her most recent entry in the Official Handbook of the Marvel Universe listed her under the name Pulsar. It is unclear if she ever used the code-name in the field - she has operated under her real name, and now currently uses the name "Spectrum."
Monica has changed her codename twice because of Genis-Vell. He first objected to her using the name Captain Marvel, originally used by his deceased father, so she became Photon. Recently, he began using the name Photon, and Monica became Pulsar.
A flashback in Nextwave revealed that she blasted a dog when she was a child, contradicting Monica's established backstory of only receiving her powers as an adult. It has yet to be explicitly confirmed whether this was intended as a new twist to Monica's history, suggesting perhaps that her powers were subsequently suppressed and only reawoken by the energy disruptor, or whether this scene should be considered a hypothetical, illustrative or imagined event. (Considering that none of Nextwave was initially intended as canonical by the writer, the latter seems more likely.)