Vital signs on the run

For fitness enthusiasts interested in tracking their vital signs while engaged in pursuits such as running, hiking or playing tennis, a newly designed pulse oximeter sensor could be a welcome and wearable accessory. The all-organic optoelectronic sensor – used for measuring pulse rate and blood oxygen saturation levels – could be sported like an adhesive bandage while mountain climbing, bicycle riding or walking the dog, to name a few examples. Importantly, the sensor could also be useful in medical clinics.

 The new device is flexible, which sets it apart from the rigid, electronics-based pulse oximeters that typically are clipped onto fingertips or earlobes in hospitals and doctors’ offices.

“Our prototype uses polymeric materials as semiconductors,” said Ana Arias, head of the University of California, Berkeley, team that created the new sensor. “These materials are flexible by nature and when processed on flexible substrates can lead to electronic devices that conform better to the human body than conventional electronics.”

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A new, all-organic optoelectronic sensor can be worn like a Band-Aid to measure pulse rate and blood oxygen saturation. OLED = organic LED. Courtesy of Yasser Khan.

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A switch to the organic, carbon-based design could enable inexpensive fabrication of the new devices. Because the components of conventional silicon-based oximeters are relatively costly, health care providers choose to disinfect contaminated oximeters, Arias noted. In contrast, she said, “organic electronics are cheap enough that they are disposable, like a Band-Aid.”

The prototype, interfaced with electronics at 1 kHz, incorporates a green (532 nm) and a red (626 nm) organic LED, and the optical signal is detected by an organic photodiode to perform blood-oxygenation measurement. To calculate the pulse, it detects the pattern of arterial blood flow. In contrast, a conventional pulse oxi meter uses LEDs to send red and infrared light through a fingertip or earlobe to obtain the blood-oxygenation measurement. Oxygen-rich blood absorbs more infrared light, while oxygen-poor blood absorbs more red light.

According to Arias, integration aspects always are challenging and, in this case, using organic materials brought an additional challenge because they are not very stable when emitting infrared light. Researchers had to modify the measurement to use green and red light instead of red and infrared. The sensor’s LEDs and detector were deposited from solution-processed materials onto a flexible piece of plastic using spin-coating and printing techniques.

The researchers found that the organic sensor measures pulse rate and oxygenation with errors of 1 and 2 percent, respectively, providing similar measurement capabilities to a commercially available pulse oximeter.

“We showed that if you take measurements with different wavelengths, it works, and if you use unconventional semiconductors, it works,” said Arias.

Arias said the team is talking to companies that are interested in commercializing the new sensor.

Applied Optoelectronics Reports Fourth Quarter and Year 2014 Results

SUGAR LAND, Texas, Feb. 25, 2015 (GLOBE NEWSWIRE) -- Applied Optoelectronics, Inc. (Nasdaq:AAOI), a leading provider of fiber-optic access network products for the internet data center, cable broadband and fiber-to-the-home markets, today announced financial results for its fourth quarter and year ended December 31, 2014.
"Fourth quarter revenue grew 53% year-over-year and we achieved record gross margin. As we reported in January, fourth quarter production was below our initial expectations due to a supply issue with an externally sourced optical sub-assembly for a new 40 Gbps data center transceiver," said Dr. Thompson Lin, Applied Optoelectronics, Inc. (AOI) founder and CEO. "Outside of this supply issue, demand for our data center products remained very high with sales inline with our expectations."

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Dr. Lin continued, "Overall for the full year our total revenue grew 66%, driven primarily by our rapid expansion in the data center optical market. We are proud to have achieved this above market growth while also improving our gross margin and significantly increasing our net income."  
Fourth Quarter 2014 Financial Summary

• Total revenue grew to $36.4 million, up 53% compared with $23.7 million in the fourth quarter 2013 and relatively unchanged compared with $36.5 million in the third quarter 2014.
• GAAP gross margin was 33.7%, compared with 28.1% in the fourth quarter 2013 and 33.2% in the third quarter 2014. Non-GAAP gross margin increased to 36.0%, compared with 28.2% in the fourth quarter 2013 and 33.3% in the third quarter 2014.
• GAAP net income was $0.7 million or $0.05 per diluted share, compared with a net loss of $0.5 million or a $0.04 loss per diluted share in the fourth quarter 2013 and net income of $1.6 million or $0.10 per diluted share in the third quarter 2014.
• Non-GAAP net income was $4.0 million or $0.27 per diluted share, compared with a non-GAAP net income of $0.3 million or $0.02 per diluted share in the fourth quarter 2013 and non-GAAP net income of $3.1 million or $0.20 per diluted share in third quarter 2014.

Full Year 2014 Financial Summary

• Total revenue grew to $130.4 million, up 66% compared with $78.4 million in 2013.
• GAAP gross margin was 33.9%, compared with 29.4% in 2013. Non-GAAP gross margin was 34.6%, compared with 29.4% in 2013.
• GAAP net income was $4.3 million or $0.28 per diluted share, compared with a net loss of $1.4 million or a $0.14 loss per diluted share in 2013. Non-GAAP net income was $10.4 million or $0.68 per diluted share, compared with a non-GAAP net income of $0.1 million or $0.01 per diluted share in 2013.
• On December 31, 2014, cash, cash equivalents and short-term investments totaled $40.9 million, an increase from the December 31, 2013 balance of $30.8 million.

A reconciliation between all GAAP and non-GAAP information referenced above is contained in the tables below. Please also refer to "Non-GAAP Financial Measures" below for a description of these non-GAAP financial measures.
First Quarter 2015 Business Outlook (+)
For the first quarter of 2015, the company currently expects:

• Revenue in the range of $35.0 million to $36.5 million
• Non-GAAP gross margin in the range of 34.0% to 35.0%
• Non-GAAP net income in the range of $2.0 million to $3.2 million, and non-GAAP fully diluted earnings per share in the range of $0.13 to $0.21 using approximately 15.3 million shares

(+) Please refer to the note below on forward-looking statements and the risks involved with such statements as well as the note on non-GAAP financial measures.
Conference Call Information
Applied Optoelectronics will host a conference call today, February 25, 2015 at 4:30 p.m. Eastern time / 3:30 p.m. Central time for analysts and investors to discuss its fourth quarter and year 2014 results and outlook for its first quarter of 2015. Open to the public, investors may access the call by dialing (719) 457-2648. A live audio webcast of the conference call along with supplemental financial information will also be accessible on the company's website at investors.ao-inc.com. Following the webcast, an archived version will be available on the website for one year. A telephonic replay of the call will be available two hours after the call and will run for five business days and may be accessed by dialing (719) 457-0820 and entering passcode 2788995.
Forward-Looking Information
This press release contains forward-looking statements. These forward-looking statements involve risks and uncertainties, as well as assumptions and current expectations, which could cause the company's actual results to differ materially from those anticipated in such forward-looking statements. These risks and uncertainties include but are not limited to: reduction in the size or quantity of customer orders; change in demand for the company's products due to industry conditions; changes in manufacturing operations; volatility in manufacturing costs; delays in shipments of products; disruptions in the supply chain; change in the rate of design wins or the rate of customer acceptance of new products; the company's reliance on a small number of customers for a substantial portion of its revenues; potential pricing pressure; a decline in demand for our customers products or their rate of deployment of their products; general conditions in the internet data center, CATV or FTTH markets; changes in the world economy (particularly in the United States and China); the negative effects of seasonality; and other risks and uncertainties described more fully in the company's documents filed with or furnished to the Securities and Exchange Commission. More information about these and other risks that may impact the company's business are set forth in the "Risk Factors" section of the company's quarterly and annual reports on file with the Securities and Exchange Commission. In some cases, you can identify forward-looking statements by terminology such as ''may,'' ''will,'' ''should,'' ''expects,'' ''plans,'' ''anticipates,'' ''believes,'' or ''estimates" or by other similar expressions that convey uncertainty of future events or outcomes. You should not rely on forward-looking statements as predictions of future events. All forward-looking statements in this press release are based upon information available to us as of the date hereof, and qualified in their entirety by this cautionary statement. Except as required by law, we assume no obligation to update forward-looking statements for any reason after the date of this press release to conform these statements to actual results or to changes in the company's expectations.
Non-GAAP Financial Measures
We provide non-GAAP gross margin, non-GAAP operating income (loss), non-GAAP net income (loss), non-GAAP earnings per share, and other non-GAAP measures like Adjusted EBITDA to eliminate the impact of items that we do not consider indicative of our overall operating performance. To arrive at our non-GAAP gross profit, we exclude stock-based compensation expense and non-recurring expenses, if any, from our GAAP gross profit. To arrive at our non-GAAP income (loss) from operations, we exclude all amortization of intangible assets, stock-based compensation expense and non-recurring expenses, if any, from our GAAP net income (loss) from operations. Included in our Q4 non-recurring expenses are items related to the relocation of our Taiwan plant and certain non-recurring expenses related to our fiber-to-the-home business. To arrive at Adjusted EBITDA, we exclude these same items and, additionally, exclude asset impairment charges, loss (gain) from disposal of idle assets, unrealized exchange loss (gain), interest (income) expense, on a net basis, provision for (benefit from) income taxes and depreciation expense, from our GAAP net income (loss). We believe that our non-GAAP measures are useful to investors in evaluating our operating performance for the following reasons:

• We believe that elimination of items such as stock-based compensation expense, non-recurring expenses, amortization and tax is appropriate because treatment of these items may vary for reasons unrelated to our overall operating performance;
• We believe that non-GAAP measures provide better comparability with our past financial performance, period-to-period results and with our peer companies, many of which also use similar non-GAAP financial measures; and
• We anticipate that investors and securities analysts will utilize non-GAAP measures to evaluate our overall operating performance.

Adjusted EBITDA and other non-GAAP measures should not be considered as an alternative to gross profit, income (loss) from operations, net income (loss) or any other measure of financial performance calculated and presented in accordance with GAAP. Our Adjusted EBITDA and other non-GAAP measures may not be comparable to similarly titled measures of other organizations because other organizations may not calculate Adjusted EBITDA or such other non-GAAP measures in the same manner.
About Applied Optoelectronics
Applied Optoelectronics, Inc. (AOI) is a leading developer and manufacturer of advanced optical products, including components, modules and equipment. AOI's products are the building blocks for broadband fiber access networks around the world, where they are used in the internet data center, CATV broadband and fiber-to-the-home markets. AOI supplies optical networking lasers, components and equipment to tier-1 customers in all three of these markets. In addition to its corporate headquarters, wafer fab and advanced engineering and production facilities in Sugar Land, TX, AOI has engineering and manufacturing facilities in Taipei, Taiwan and Ningbo, China.
For additional information, visit www.ao-inc.com. Applied Optoelectronics, Inc. and the related AOI logo are trademarks of Applied Optoelectronics, Inc.

Applied Optoelectronics, Inc.
Preliminary Condensed Consolidated Balance Sheets
(In thousands, except per share data)
(Unaudited)
	December 31, 2014	December 31, 2013
ASSETS
CURRENT ASSETS
Cash, Cash Equivalents and Short term investments	$ 40,873	$ 30,751
Accounts Receivable, Net	31,589	22,089
Inventories	33,780	19,608
Notes Receivable	980	--
Prepaid Expenses and Other Current Assets	6,017	5,488
Total Current Assets	113,239	77,936
Property, Plant And Equipment, Net	64,808	31,134
Land Use Rights, Net	930	959
Intangible Assets, net	3,833	851
Other Assets	860	177
TOTAL ASSETS	$ 183,670	$ 111,057
LIABILITIES AND STOCKHOLDERS' EQUITY
CURRENT LIABILITIES
Accounts Payable	$ 30,799	$ 15,010
Accrued Expenses	6,940	4,515
Bank Acceptance Payable	1,271	2,347
Bank Loan-Short Term	8,205	13,260
Current Portion of Long Term Debt	1,386	3,925
Total Current Liabilities	48,601	39,057
Notes Payable and Long Term Debt	19,057	8,923
Other Long Term liabilities	1,000	--
TOTAL LIABILITIES	68,658	47,980
TOTAL STOCKHOLDERS' EQUITY	115,012	63,077
Total Liabilities, redeemable preferred stock and stockholders' equity	$ 183,670	$ 111,057

Applied Optoelectronics, Inc.
Preliminary Condensed Consolidated Statements of Operations
(In thousands, except per share data)
(Unaudited)
	Three Months Ended December 31,		Twelve Months Ended December 31,
Revenue	2014	2013	2014	2013
CATV	$ 14,749	$ 14,041	$ 47,389	$ 47,373
Datacenter	14,923	5,910	64,453	19,386
FTTH	5,663	1,603	13,591	4,377
Other	1,056	2,190	5,016	7,288
Total Revenue	36,391	23,744	130,449	78,424
Total Cost of Goods Sold	24,132	17,068	86,203	55,396
Total Gross Profit	12,259	6,676	44,246	23,028
Operating Expenses:
Research & Development	4,221	2,400	15,970	8,512
Sales and Marketing	1,591	1,198	6,043	4,191
General and administrative	5,131	3,375	17,095	10,632
Total Operating Expenses	10,943	6,973	39,108	23,335
Operating Income (Loss)	1,316	(297)	5,138	(307)
Other Income (Expense):
Interest Income	89	55	369	104
Interest Expense	(50)	(200)	(326)	(1,125)
Other Income	208	69	302	334
Other Expense	(849)	(147)	(1,001)	(412)
Total Other Income (Expenses):	(602)	(223)	(656)	(1,099)
Net Income (loss) before Income Taxes	714	(520)	4,482	(1,406)
Income Tax	(12)	--	(199)	--
Net Income (loss)	$ 702	$ (520)	$ 4,283	$ (1,406)
Net income (loss) per share attributable to common stockholders
basic	$ 0.05	$ (0.04)	$ 0.30	$ (0.14)
diluted	$ 0.05	$ (0.04)	$ 0.28	$ (0.14)
Weighted-average shares used to compute net income (loss) per share attributable to common stockholders
basic	14,819	12,631	14,307	9,965
diluted	15,207	12,631	15,187	9,965

Applied Optoelectronics, Inc.
Preliminary Condensed Consolidated NON GAAP Statements of Operations
(In thousands, except per share data)
(Unaudited)
	Three Months Ended December 31,		Twelve Months Ended December 31,
Revenue	2014	2013	2014	2013
CATV	$ 14,749	$ 14,041	$ 47,389	$ 47,373
Datacenter	14,923	5,910	64,453	19,386
FTTH	5,663	1,603	13,591	4,377
Other	1,056	2,190	5,016	7,288
Total Revenue	36,391	23,744	130,449	78,424
Total Cost of Goods Sold	23,308	17,052	85,317	55,340
Total Gross Profit	13,083	6,692	45,132	23,084
Operating Expenses:
Research & Development	4,190	2,383	15,855	8,459
Sales and Marketing	1,566	1,178	5,946	4,139
General and administrative	3,762	2,718	13,419	9,622
Total Operating Expenses	9,518	6,279	35,220	22,220
Operating Income (Loss)	3,565	413	9,912	864
Other Income (Expense):
Interest Income	89	55	369	104
Interest Expense	(50)	(200)	(326)	(1,125)
Other Income / Expense	453	7	601	264
Total Other Income (Expenses):	492	(138)	644	(757)
Net Income (loss) before Income Taxes	4,057	275	10,556	107
Income Tax	(12)	--	(199)	--
Net Income (loss)	$ 4,045	$ 275	$ 10,357	$ 107
Net income (loss) per share attributable to common stockholders
basic	$ 0.27	$ 0.02	$ 0.72	$ 0.01
diluted	$ 0.27	$ 0.02	$ 0.68	$ 0.01
Weighted-average shares used to compute net income (loss) per share attributable to common stockholders
basic	14,819	12,631	14,307	9,965
diluted	15,207	13,291	15,187	10,626

Applied Optoelectronics, Inc.
Preliminary Condensed Consolidated Statements of Operations
(In thousands, except per share data)
(Unaudited)
	Three Months Ended December 31,		Twelve Months Ended December 31,
	2014	2013	2014	2013
GAAP total gross profit	$ 12,259	$ 6,676	$ 44,246	$ 23,028
Share-based compensation expense	27	16	89	56
Non Recurring expense	797	--	797	--
Non-GAAP income (loss) from gross profit	13,083	6,692	45,132	23,084
GAAP research and development expense	4,221	2,400	15,970	8,512
Share-based compensation expense	31	17	115	53
Non-GAAP research and development expense	4,190	2,383	15,855	8,459
GAAP sales and marketing expense	1,591	1,198	6,043	4,191
Share-based compensation expense	25	20	97	52
Non-GAAP sales and marketing expense	1,566	1,178	5,946	4,139
GAAP general and administrative expense	5,131	3,375	17,095	10,632
Share-based compensation expense	483	640	1,759	907
Amortization expense	98	17	356	68
Non Recurring expense	788	--	1,561	35
Non-GAAP general and administrative expense	3,762	2,718	13,419	9,622
GAAP total operating expense	10,943	6,973	39,108	23,335
Share-based compensation expense	539	677	1,971	1,012
Amortization expense	98	17	356	68
Non Recurring expense	788	--	1,561	35
Non-GAAP total operating expense	9,518	6,279	35,220	22,220
GAAP operating income (loss)	1,316	(297)	5,138	(307)
Share-based compensation expense	566	693	2,060	1,068
Amortization expense	98	17	356	68
Non Recurring expense	1,585	--	2,358	35
Non-GAAP operating income (loss)	3,565	413	9,912	864
GAAP other income (loss)	(602)	(223)	(656)	(1,099)
Unrealized exchange loss (gain)	1,094	85	1,300	342
Non-GAAP other income (loss)	492	(138)	644	(757)
GAAP net income (loss)	702	(520)	4,283	(1,406)
Amortization of intangible assets	98	17	356	68
Share-based compensation expense	566	693	2,060	1,068
Non Recurring charges	1,585	--	2,358	35
Unrealized exchange loss (gain)	1,094	85	1,300	342
Non-GAAP net income (loss)	4,045	275	10,357	107
GAAP net income (loss)	702	(520)	4,283	(1,406)
Amortization of intangible assets	98	17	356	68
Share-based compensation expense	566	693	2,060	1,068
Depreciation expense	1,722	954	5,813	3,339
Non Recurring charges	1,585	--	2,358	35
Unrealized exchange loss (gain)	1,094	85	1,300	342
Interest (income) expense, net	(39)	145	(43)	1,021
Taxes related to the above	12	--	199	--
Adjusted EBITDA	$ 5,740	$ 1,374	$ 16,326	$ 4,467

X-ray

X-radiation (composed of X-rays) is a form of electromagnetic radiation. Most X-rays have a wavelength ranging from 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz (3×10¹⁶ Hz to 3×10¹⁹ Hz) and energies in the range 100 eV to 100 keV. X-ray wavelengths are shorter than those of UV rays and typically longer than those of gamma rays. In many languages, X-radiation is referred to with terms meaning Röntgen radiation, after Wilhelm Röntgen,^[1] who is usually credited as its discoverer, and who had named it X-radiation to signify an unknown type of radiation.^[2] Spelling of X-ray(s) in the English language includes the variants x-ray(s), xray(s) and X ray(s).^[3]

X-rays with photon energies above 5–10 keV (below 0.2–0.1 nm wavelength) are called hard X-rays, while those with lower energy are called soft X-rays.^[4] Due to their penetrating ability, hard X-rays are widely used to image the inside of objects, e.g., in medical radiography and airport security. As a result, the term X-ray is metonymically used to refer to a radiographic image produced using this method, in addition to the method itself. Since the wavelengths of hard X-rays are similar to the size of atoms they are also useful for determining crystal structures by X-ray crystallography. By contrast, soft X-rays are easily absorbed in air and the attenuation length of 600 eV (~2 nm) X-rays in water is less than 1 micrometer.^[5]

There is no universal consensus for a definition distinguishing between X-rays and gamma rays. One common practice is to distinguish between the two types of radiation based on their source: X-rays are emitted by electrons, while gamma rays are emitted by the atomic nucleus.^[6][7][8][9] This definition has several problems; other processes also can generate these high energy photons, or sometimes the method of generation is not known. One common alternative is to distinguish X- and gamma radiation on the basis of wavelength (or equivalently, frequency or photon energy), with radiation shorter than some arbitrary wavelength, such as 10⁻¹¹ m (0.1 Å), defined as gamma radiation.^[10] This criterion assigns a photon to an unambiguous category, but is only possible if wavelength is known. (Some measurement techniques do not distinguish between detected wavelengths.) However, these two definitions often coincide since the electromagnetic radiation emitted by X-ray tubes generally has a longer wavelength and lower photon energy than the radiation emitted by radioactive nuclei.^[6] Occasionally, one term or the other is used in specific contexts due to historical precedent, based on measurement (detection) technique, or based on their intended use rather than their wavelength or source. Thus, gamma-rays generated for medical and industrial uses, for example radiotherapy, in the ranges of 6–20 MeV, can in this context also be referred to as X-rays.

gamma ray-2

Sources of gamma rays

Natural sources of gamma rays on Earth include gamma decay from naturally occurring radioisotopes such as potassium-40, and also as a secondary radiation from various atmospheric interactions with cosmic ray particles. Some rare terrestrial natural sources that produce gamma rays that are not of a nuclear origin, are lightning strikes and terrestrial gamma-ray flashes, which produce high energy emissions from natural high-energy voltages. Gamma rays are produced by a number of astronomical processes in which very high-energy electrons are produced. Such electrons produce secondary gamma rays by the mechanisms of bremsstrahlung, inverse Compton scattering and synchrotron radiation. A large fraction of such astronomical gamma rays are screened by Earth's atmosphere and must be detected by spacecraft. Notable artificial sources of gamma rays include fission such as occurs in nuclear reactors, and high energy physics experiments, such as neutral pion decay and nuclear fusion.

General characteristics

The distinction between X-rays and gamma rays has changed in recent decades. Originally, the electromagnetic radiation emitted by X-ray tubes almost invariably had a longer wavelength than the radiation (gamma rays) emitted by radioactive nuclei.^[6] Older literature distinguished between X- and gamma radiation on the basis of wavelength, with radiation shorter than some arbitrary wavelength, such as 10⁻¹¹ m, defined as gamma rays.^[7] However, with artificial sources now able to duplicate any electromagnetic radiation that originates in the nucleus, as well as far higher energies, the wavelengths characteristic of radioactive gamma ray sources vs. other types, now completely overlap. Thus, gamma rays are now usually distinguished by their origin: X-rays are emitted by definition by electrons outside the nucleus, while gamma rays are emitted by the nucleus.^{[6][8][9][10]} Exceptions to this convention occur in astronomy, where gamma decay is seen in the afterglow of certain supernovas, but other high energy processes known to involve other than radioactive decay are still classed as sources of gamma radiation.

Naming conventions and overlap in terminology

In the past, the distinction between X-rays and gamma rays was based on energy, with gamma rays being considered a higher-energy version of electromagnetic radiation. However, modern high-energy X-rays produced by linear accelerators for megavoltage treatment in cancer often have higher energy (4 to 25 MeV) than do most classical gamma rays produced by nuclear gamma decay. One of the most common gamma ray emitting isotopes used in diagnostic nuclear medicine, technetium-99m, produces gamma radiation of the same energy (140 keV) as that produced by diagnostic X-ray machines, but of significantly lower energy than therapeutic photons from linear particle accelerators. In the medical community today, the convention that radiation produced by nuclear decay is the only type referred to as "gamma" radiation is still respected.

Because of this broad overlap in energy ranges, in physics the two types of electromagnetic radiation are now often defined by their origin: X-rays are emitted by electrons (either in orbitals outside of the nucleus, or while being accelerated to produce bremsstrahlung-type radiation),^[12] while gamma rays are emitted by the nucleus or by means of other particle decays or annihilation events. There is no lower limit to the energy of photons produced by nuclear reactions, and thus ultraviolet or lower energy photons produced by these processes would also be defined as "gamma rays".^[13] The only naming-convention that is still universally respected is the rule that electromagnetic radiation that is known to be of atomic nuclear origin is always referred to as "gamma rays," and never as X-rays. However, in physics and astronomy, the converse convention (that all gamma rays are considered to be of nuclear origin) is frequently violated.

In astronomy, higher energy gamma and X-rays are defined by energy, since the processes which produce them may be uncertain and photon energy, not origin, determines the required astronomical detectors needed.^[14] High energy photons occur in nature which are known to be produced by processes other than nuclear decay but are still referred to as gamma radiation. An example is "gamma rays" from lightning discharges at 10 to 20 MeV, and known to be produced by the bremsstrahlung mechanism.

Another example is gamma-ray bursts, now known to be produced from processes too powerful to involve simple collections of atoms undergoing radioactive decay. This has led to the realization that many gamma rays produced in astronomical processes result not from radioactive decay or particle annihilation, but rather in much the same manner as the production of X-rays. Although gamma rays in astronomy are discussed below as non-radioactive events, in fact a few gamma rays are known in astronomy to originate explicitly from gamma decay of nuclei (as demonstrated by their spectra and emission half life). A classic example is that of supernova SN 1987A, which emits an "afterglow" of gamma-ray photons from the decay of newly made radioactive nickel-56 and cobalt-56. Most gamma rays in astronomy, however, arise by other mechanisms. Astronomical literature tends to write "gamma-ray" with a hyphen,^{[citation needed]} by analogy to X-rays, rather than in a way analogous to alpha rays and beta rays. This notation tends to subtly stress the non-nuclear source of most astronomical "gamma-rays."

Gamma Ray-1

Illustration of an emission of a gamma ray (γ) from an atomic nucleus

Gamma radiation, also known as gamma rays, and denoted by the Greek letter γ, refers to electromagnetic radiation of an extremely high frequency and are therefore high energy photons. Gamma rays are ionizing radiation, and are thus biologically hazardous. They are classically produced by the decay of atomic nuclei as they transition from a high energy state to a lower state known as gamma decay, but may also be produced by other processes. Paul Villard, a French chemist and physicist, discovered gamma radiation in 1900, while studying radiation emitted from radium. Villard's radiation was named "gamma rays" by Ernest Rutherford in 1903.

Natural sources of gamma rays on Earth include gamma decay from naturally occurring radioisotopes, and secondary radiation from atmospheric interactions with cosmic ray particles. Rare terrestrial natural sources produce gamma rays that are not of a nuclear origin, such as lightning strikes and terrestrial gamma-ray flashes. Additionally, gamma rays are produced by a number of astronomical processes in which very high-energy electrons are produced, that in turn cause secondary gamma rays via bremsstrahlung, inverse Compton scattering and synchrotron radiation. However, a large fraction of such astronomical gamma rays are screened by Earth's atmosphere and can only be detected by spacecraft.

Gamma rays typically have frequencies above 10 exahertz (or >10¹⁹ Hz), and therefore have energies above 100 keV and wavelengths less than 10 picometers (10⁻¹² meter), which is less than the diameter of an atom. However, this is not a hard and fast definition, but rather only a rule-of-thumb description for natural processes. Electromagnetic radiation from radioactive decay of atomic nuclei is referred to as "gamma rays" no matter its energy, so that there is no lower limit to gamma energy derived from radioactive decay. This radiation commonly has energy of a few hundred keV, and almost always less than 10 MeV. In astronomy, gamma rays are defined by their energy, and no production process needs to be specified. The energies of gamma rays from astronomical sources range to over 10 TeV, an energy far too large to result from radioactive decay.^[1] A notable example is extremely powerful bursts of high-energy radiation referred to as long duration gamma-ray bursts, of energies higher than can be produced by radioactive decay. These bursts of gamma rays, thought to be due to the collapse of stars called hypernovae, are the most powerful events so far discovered in the cosmos.

Gamma rays are emitted during nuclear fission in nuclear explosions.

History of discovery

The first gamma ray source to be discovered historically was the radioactive decay process called gamma decay. In this type of decay, an excited nucleus emits a gamma ray almost immediately upon formation (it is now understood that a nuclear isomeric transition, however, can produce inhibited gamma decay with a measurable and much longer half-life). Paul Villard, a French chemist and physicist, discovered gamma radiation in 1900, while studying radiation emitted from radium. Villard knew that his described radiation was more powerful than previously described types of rays from radium, which included beta rays, first noted as "radioactivity" by Henri Becquerel in 1896, and alpha rays, discovered as a less penetrating form of radiation by Rutherford, in 1899. However, Villard did not consider naming them as a different fundamental type.^[2][3] Villard's radiation was recognized as being of a type fundamentally different from previously named rays, by Ernest Rutherford, who in 1903 named Villard's rays "gamma rays" by analogy with the beta and alpha rays that Rutherford had differentiated in 1899.^[4] The "rays" emitted by radioactive elements were named in order of their power to penetrate various materials, using the first three letters of the Greek alphabet: alpha rays as the least penetrating, followed by beta rays, followed by gamma rays as the most penetrating. Rutherford also noted that gamma rays were not deflected (or at least, not easily deflected) by a magnetic field, another property making them unlike alpha and beta rays.

Gamma rays were first thought to be particles with mass, like alpha and beta rays. Rutherford initially believed they might be extremely fast beta particles, but their failure to be deflected by a magnetic field indicated they had no charge.^[5] In 1914, gamma rays were observed to be reflected from crystal surfaces, proving they were electromagnetic radiation.^[5] Rutherford and his coworker Edward Andrade measured the wavelengths of gamma rays from radium, and found that they were similar to X-rays but with shorter wavelengths and (thus) higher frequency. This was eventually recognized as giving them also more energy per photon, as soon as the latter term became generally accepted. A gamma decay was then understood to usually emit a single gamma photon.

Mengubah Udara Hampa Jadi Serat Optik

Sejumlah peneliti berhasil melakukan ujicoba perubahan udara hampa menjadi serat optik yang dapat mentransmisi sinyal tanpa diperlukan adanya kabel.

Ilmuwan temukan cara untuk mengubah udara menjadi serat optik. (Credit: ABC) 

“Untuk beberapa waktu belakangan, banyak orang sudah berpikiran untuk membuat jaringan udara ini, namun baru kali ini hal ini tercapai,” kata Professor Howard Milchberg dari University of Maryland, pemimpin dari riset yang didanai oleh Militer AS dan National Science Foundation. Pada eksperimen ulang untuk membuktikan teori ini, mereka menciptakan sebuah jaringan udara yang kelak dapat digunakan sebagai serat optic instant yang dapat digunakan dibagian manapun di dunia atau bahkan ruang angkasa. Penemuan yang ditulis di jurnal Optica ini memiliki aplikasia antara lain komunikasi laser jarak jauh, pemetaan topografi beresolusi tinggi, riset sehubungan dengan polusi udara dan perubahan iklim, dan bahkan di dunia militer untuk membuat senjata laser. Laser pada umumnya akan kehilangan focus dan intensitasnya seiring dengan bertambahnya jarak yang dikarenakan oleh photon yang secara natural terpisah dan berinteraksi dengan atom dan molekul lain yang ada di udara.

Serat optik memechakan permasalahan ini dengan menembakkan cahaya melalui cermin dengan daya pantul kuat yang berfungsi sangat efektif untuk mentransmisi cahaya. Cermin itu akan dikelilingi oleh materi yang memiliki daya pantul rendah yang akan memantulkan kembali cahaya ke cermin, Mencegah laser kehilangan focus dan intensitasnya. Terlepas dari itu, kemampuan serat optic untuk membawa energi masihlah terbatas dan akan membutuhkan struktur fisik untuk membantunya membawa energi tersebut. Milchberg dan rekannya telah menemukan sesuatu yang mirip dengan serat optik dari udara dengan menggabungkan laser dan cahayanya kedalam sebuah pipa yang dibentuk dari berbagai tembakan laser. Mereka menggunakan tembakan yang pendek namun sangat kuat dari laser untuk memanaskan permukaan udara sepanjang jalur tembakan. Proses pemanasan yang cepat akan menimbulkan jaringan suara yang dalam waktu sekitar satu detik mikro akan mencapai inti dari pipa, menimbulkan area yang sangat padat.

“Satu detik mikro itu termasuk lama apabila dibandingkan dengan waktu yang dibutuhkan untuk cahaya dapat menyebar, sehingga ketika cahaya itu sudah hilang, satu detik mikro kemudian jaringan suara mertemu di tengah, memperbesar kepadatan udara di tempat tersebut,” kata Milchberg.

Kepadatan yang lebih rendah di daerah yang mengelilingi bagian tengah dari jaringan udara memiliki daya pantul yang lebih rendah, menjaga cahaya untuk tetap fokus. “Struktur apapun [bahkan udara] yang memiliki nilai kepadatan tinggi akan memiliki daya pantul yang lebih kuat dan dapat bekerja sebagai serat optik,” tambah Milchberg. Begitu Milchberg dan rekan rekannya menciptakan jaringan udara tersebut, mereka menggunakan laser susulan untuk memancing percikan udara di ujung dari jaringan dan merubahnya menjadi plasma. Sinyal optik dari percikan itu akan tertransmisi sepanjang jaringan udara, sejauh satu meter ke alat pendeteksi di ujung lainnya. Sinyal yang diterima oleh alat pendeteksi tersebut cukup kuat untuk memperbolehkan Milchberg dan rekan rekannya untuk menganalisa kandungan kimia yang diproduksi oleh percikan tersebut. Para ilmuwan ini menemukan bahwa sinyal tersebut 50 per sen lebih kuat dari sinyal yang tidak menggunakan jaringan udara. Pakar Australia Proffesor Ben Eggleton dari University of Sydney mengatakan bahwa penemuan ini sangat penting untuk bidang optik. “Ini seperti jika kami memiliki serat optic dan dapat menyinarkannya ke lanigt, menghubungkan laser anda ke ujung atmosfer,” kata Eggleton. “Anda tidak lagi memerlukan lensa yang besar dan optik.”

sumber: http://www.radioaustralia.net.au/indonesian/2014-07-23/berhasil-diujicoba-mengubah-udara-hampa-jadi-serat-optik/1346821

Sensor Cahaya

Sensor dan transduser merupakan peralatan atau komponen yang mempunyai peranan penting dalam sebuah sistem pengaturan otomatis. Ketepatan dan kesesuaian dalam memilih sebuah sensor akan sangat menentukan kinerja dari sistem pengaturan secara otomatis. Besaran masukan pada kebanyakan sistem kendali adalah bukan besaran listrik, seperti besaran fisika, kimia, mekanis dan sebagainya. Untuk memakaikan besaran listrik pada sistem pengukuran, atau sistem manipulasi atau sistem pengontrolan, maka biasanya besaran yang bukan listrik diubah terlebih dahulu menjadi suatu sinyal listrik melalui sebuah alat yang disebut transducer .
D Sharon, dkk (1982), mengatakan sensor adalah suatu peralatan yang berfungsi untuk mendeteksi gejala-gejala atau sinyal-sinyal yang berasal dari perubahan suatu energi seperti energi listrik, energi fisika, energi kimia, energi biologi, energi mekanik dan sebagainya. Contoh; Camera sebagai sensor penglihatan, telinga sebagai sensor pendengaran, kulit sebagai sensor peraba, LDR (light dependent resistance) sebagai sensor cahaya, dan lainnya.
William D.C, (1993), mengatakan transduser adalah sebuah alat yang bila digerakan oleh suatu energi di dalam sebuah sistem transmisi, akan menyalurkan energi tersebut dalam bentuk yang sama atau dalam bentuk yang berlainan ke sistem transmisi berikutnya”. Transmisi energi ini bisa berupa listrik, mekanik, kimia, optic (radiasi) atau thermal (panas). Contoh; generator adalah transduser yang merubah energi mekanik menjadi energi listrik, motor adalah transduser yang merubah energi listrik menjadi energi mekanik, dan sebagainya.
Sensor optic atau cahaya adalah sensor yang mendeteksi perubahan cahaya dari sumber cahaya, pantulan cahaya ataupun bias cahaya yang mengenai benda atau ruangan. Contoh; photo cell, photo transistor, photo diode, photo voltaic, photo multiplier, pyrometer optic, dsb.
Elemen-elemen sensitive cahaya merupakan alat terandalkan untuk mendeteksi energi cahaya. Alat ini melebihi sensitivitas mata manusia terhadap semua spectrum warna dan juga bekerja dalam daerah-daerah ultraviolet dan infra merah. Energi cahaya bila diolah dengan cara yang tepat akan dapat dimanfaatkan secara maksimal untuk teknik pengukuran, teknik pengontrolan dan teknik kompensasi.
Penggunaan praktis alat sensitif cahaya ditemukan dalam berbagai pemakaian teknik seperti halnya :
Tabung cahaya atau fototabung vakum (vaccum type phototubes), paling§ menguntungkan digunakan dalam pemakaian yang memerlukan pengamatan pulsa cahaya yang waktunya singkat, atau cahaya yang dimodulasi pada frekuensi yang relative tinggi. Tabung cahaya gas (gas type phototubes), digunakan dalam industri gambar hidup sebagai pengindra suara pada film.§ Tabung cahaya pengali atau pemfotodarap (multiplier phottubes), dengan§ kemampuan penguatan yang sangat tinggi, sangat banyak digunakan pada pengukuran fotoelektrik dan alat-alat kontrol dan juga sebagai alat cacah kelipan (scientillation counter). sel-sel fotokonduktif (photoconductive cell), juga disebut tahanan§ cahaya (photo resistor) atau tahanan yang bergantung cahaya (LDR-light dependent resistor), dipakai luas dalam industri dan penerapan pengontrolan di laboratorium.
Sel-sel foto tegangan (photovoltatic cells), adalah alat semikonduktor§ untuk mengubah energi radiasi daya listrik. Contoh yang sangat baik adalah sel matahari (solar cell) yang digunakan dalam teknik ruang angkasa.